EEVblog #238 - Power Supply Design Part 7. - Page 1
Forum section: electronics / general

author: firewalker
author_rank: Super Contributor
timestamp: January 19, 2012, 03:14:00 pm
content: Alexander.

author: hans
author_rank: Super Contributor
timestamp: January 19, 2012, 06:22:17 pm
content: I think it may be possible to reduce the component count by removing the pull-up resistors on the input switches. I have used the MCP23S17 before for reading switches (for a joystick) and used the internal pullups. The datasheet also mentions and documents a register for it (register GPPU)The uCurrent seems like very sensitive to me. 500 gain introduces a ton of noise. Let's not forget that the output noise of the opamp is 1.5uVp-p (RTI). If you amplify it by 500, that's about 0.75mVpp noise. The ADC samples 0.5mV steps, so it will require a bit more oversampling to get a completely 'silent' readout. Nevertheless, more resolution = better.

author: thilo
author_rank: Regular Contributor
timestamp: January 19, 2012, 06:26:03 pm
content: It turned from a nice little power supply in a feature creeped monster

author: firewalker
author_rank: Super Contributor
timestamp: January 19, 2012, 07:17:02 pm
content: Dave would it be nice to use opamps with supply voltage at least to 22~30 volts in order to enable people to modify it easily for higher voltage?Alexander.

author: ejeffrey
author_rank: Super Contributor
timestamp: January 19, 2012, 08:54:01 pm
content: Dave, what is the reason to use soft SPI instead of sharing the pins with the ISP? I would have assumed that as long as the chip-select pins were off during programming the other devices on the bus wouldn't interfere with the programming.Also, if you were starting over would you reconsider using a capacitive switcher in to generate a negative rail? It seems like even a 10 milliamp negative supply would have made a number of issues easier, but presumably that would come with its own issues.

author: mightyzen
author_rank: Contributor
timestamp: January 19, 2012, 09:10:20 pm
content: Dave, I think you misread the TLC272 data sheet. Texas did not mix up A, B and C grades. The TLC272CD is not the C-grade, it is the grade-less. C = 0-70C, D = SO-package. The TLC272ACD is the better A-grade, the TLC272BCD is the even better B-grade. There is no C-grade.Why don't you add a simple negative voltage generator (eg TC7660) to your design? Then you could use the cheapest standard op amps, like the lm258 or ka258.

author: jpelczar
author_rank: Contributor
timestamp: January 19, 2012, 09:11:37 pm
content: Quote from: ejeffrey on January 19, 2012, 08:54:01 pmOr one could use 4053 like here:http://www.btc.pl/pdf/zl12avr.pdf

author: fmaimon
author_rank: Unknown
timestamp: January 19, 2012, 09:23:28 pm
content: You can´t and don´t need to leave that 100nF capacitor on the reset pin. Just a single 10k resistor is enough. The AVR reset have a internal filter to discard noise and a capacitor will disturb the signals going to/from reset if you want to use debugWire in the m168.

author: McMonster
author_rank: Frequent Contributor
timestamp: January 19, 2012, 09:49:09 pm
content: Quote from: ejeffrey on January 19, 2012, 08:54:01 pmI don't think it'll matter now, Dave mentioned in other thread the project already went into production. But, should it matter for any possible future revisions it's much simpler. There's an AVR042 application note about hardware considerations for AVR chips with states that putting series resistors on SPI lines is all you need for proper ISP functioning even if there are other devices trying to drive those lines. So in my opinion it's worth considering if there'll be any new board version, hardware interface means simpler code.And great work with expansion connectors, people can't really complain on the lack of modding possibilities. I just hope nobody will mention arduino shields now, there's simply no point

author: Bored@Work
author_rank: Super Contributor
timestamp: January 19, 2012, 09:59:01 pm
content: Quote from: McMonster on January 19, 2012, 09:49:09 pmI previously pointed Dave to it, he didn't seem to be much interested. I was also surprised to hear his reasoning for changing the LED on the reset pin "after reading the datasheet". While this was in fact something pointed out be me in the forumhttps://www.eevblog.com/forum/index.php?topic=6163.msg80321#msg80321

author: firewalker
author_rank: Super Contributor
timestamp: January 19, 2012, 10:17:11 pm
content: I believe he did it in order to have the SPI available for any kind of Arduino control modules that need it.Alexander.Quote from: ejeffrey on January 19, 2012, 08:54:01 pm

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 19, 2012, 10:31:17 pm
content: Don't know where you got the pinout for the UART ins on your header but most of the ones I've seen use the pinout of FTDI's TTL-232 cable, which doesn't match what you have there.

author: amspire
author_rank: Super Contributor
timestamp: January 19, 2012, 10:52:14 pm
content: Quote from: McMonster on January 19, 2012, 09:49:09 pmSorry to dash your hopes, but I still think that to eliminate the chance to use a Ethernet interface is a big mistake. And the only most practical way of adding Ethernet is to use the $20 (delivered) shield.Any computer interface has to be isolated, and the serial based USB is just ugly compared to USB.Ethernet means you don't have to have a computer on the same bench, you get 1500V isolation, you do not need a program to talk to the power supply since you can use a browser, you get the SD socket, so you can have unlimited storage space for data logging, you never have to sort out some piece of software that has to work out what virtual serial port the USB is using, since it changes for each different USB port, if you have a wireless router on your network, you get wireless access from notebooks, ipads, phones, etc, you can have banks of power supplies that can all talk to one computer.You get all of this merely by freeing up a few more pins.In case anyone thinks accessing the power supply via a browser means some heavy duty stuff - that is wrong. A basic web server is one of the simplest programs you can write. You listen for a GET command string, and send back your data along with some stored HTML strings. To get started, that is all that is needed.Now that Ethernet seems to have been ruled out, someone will have to design the isolated RS232 or USB ports, and they will either have to use a terminal program (missing in Windows 7), or actually write a custom interface program. All that extra work for the sake of 2 pins on the Arduino.Richard

author: firewalker
author_rank: Super Contributor
timestamp: January 19, 2012, 11:05:01 pm
content: In what way the ethernet shield is ruled out?Alexander.

author: jerry507
author_rank: Regular Contributor
timestamp: January 19, 2012, 11:05:27 pm
content: Quote from: BoredAtWork on January 19, 2012, 09:59:01 pmReally that hard up for the recognition?The statement certainly didn't imply that he found it after that, just that it was not something obvious and was "buried in the datasheet."

author: Bored@Work
author_rank: Super Contributor
timestamp: January 19, 2012, 11:27:46 pm
content: Quote from: jerry507 on January 19, 2012, 11:05:27 pmI am just surprised. Dave did a number of corrections as suggested by forum members. I would have expected a nod to the forum. Of course I do understand he needs to keep up a certain image in his videos.

author: amspire
author_rank: Super Contributor
timestamp: January 20, 2012, 12:18:58 am
content: Quote from: firewalker on January 19, 2012, 11:05:01 pmLooking again, and you may be right. If the pin labelled SS is unused, then the Ethernet part of the Ethernet shield at least could be used. For some reason I thought that pin had been assigned to PS hardware, but I think I was wrong.The SD memory enable pin (PD3) has been allocated for the rotary encoder. I guess if another spare pin can be found, you could edit the pin allocation in the library and regain access to the SD slot.Does anyone know where the link to the new schematic PDF is? I tried thehttp://www.eevblog.com/uploads/folder but only RevA is there right now.

author: Psi
author_rank: Super Contributor
timestamp: January 20, 2012, 12:29:13 am
content: Quote from: BoredAtWork on January 19, 2012, 11:27:46 pmIt's not scripted, he can't be expected to remember everything on demand.

author: ThanksBAW
author_rank: Newbie
timestamp: January 20, 2012, 12:59:39 am
content: Hope this helps!

author: jshonw
author_rank: Contributor
timestamp: January 20, 2012, 02:55:08 am
content: As mentioned already, the cap on the reset pin will interfere with debugWIRE. But, it's good for the added protection against noise if you are not using it. So, if I build it, I will just leave it out.

author: McMonster
author_rank: Frequent Contributor
timestamp: January 20, 2012, 03:43:54 am
content: Quote from: amspire on January 19, 2012, 10:52:14 pmI'm not against Ethernet shiled as a rule, it would be nice to have it, but I don't think it would be practical in this particular project. The design would have to be made around it, making space on the board for headers and arranging everything so that its' position makes sense with the case. By the way, wouldn't the new connectors be enough to make a simple adapter board for this shield?

author: reagle
author_rank: Unknown
timestamp: January 20, 2012, 04:17:49 am
content: Noticed the buttons did not seem to have any ESD protection around them- they just go directly to the IO expander if I remember correctly. I'd at least slap a small cap across each one and maybe a series element?

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 09:09:24 am
content: Quote from: amspire on January 20, 2012, 12:18:58 amIs the SD memory enable pin actually required?I was ensuring that all the SPI/SS pins were available to enable that Ethernet shield (or your own designed board) could be hacked in.QuoteIt's there now.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 09:12:10 am
content: Quote from: jerry507 on January 19, 2012, 11:05:27 pmSeveral people in fact pointed out the RESET pin issue.Sorry if you feel you didn't get recognition BAW.Dave.

author: firewalker
author_rank: Super Contributor
timestamp: January 20, 2012, 09:14:07 am
content: I will be really easy to use any pin from the port expander under Arduino IDE.Alexander.

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 09:16:36 am
content: Quote from: BoredAtWork on January 19, 2012, 11:27:46 pmThe suggestions came from everywhere. The forum, youtube and blog comments, and email.All of them had in fact already been considered in some form at various points in the design process except for the RESET pin problem which I had indeed overlooked.In fact I've had so many suggestions (and complaints) that I am almost regretting doing the project in this blog-as-I-go mannerIt's really not a good way to do it because I'm always revising my designs, and in many cases, completely changing my mind and scrapping and starting again. Wouldn't THAT piss off a lot of people!Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 09:35:21 am
content: Quote from: McMonster on January 20, 2012, 03:43:54 amYou are correct McM. The standard case I'm using is way too short for any shield, and the taller case might just fit an Arduino shield but I'd have to check. So if I wanted to save cost on the kit I'd have to supply the smaller case that doesn't fit the shield, or use the taller more expensive case for everyone.I'd also would have had to design the (already very cramped) PCB around the shield. Possible, but I'd have to scrap the layout and start again likely.As it stands it can be wired in.Dave.

author: firewalker
author_rank: Super Contributor
timestamp: January 20, 2012, 09:44:43 am
content: I agree no need for more "Social engineering" for this project.Alexander.

author: shebu18
author_rank: Frequent Contributor
timestamp: January 20, 2012, 10:40:02 am
content: For the FTDI bus you need RX/TX/DTR/GND and maybe 5V. Between the DTR and RESET should be a 10nF(i think,need to review that) capacitor or else you will have problems with the arduino type of programing. i had that happen and after adding the cap it all got solved.In the arduino IDE you will get a out of sync error.

author: Unknown
author_rank: Unknown
timestamp: January 20, 2012, 11:20:10 am
content: Quote from: firewalker on January 20, 2012, 09:44:43 amI hear you. There is an important lesson here for anybody who wants to release anything open source.What I've learned at Dave's expense is1-Do not release until you have something working at hand. If help is needed before release, seek it in a closed circle of people, not publicly. Do not allow your idea to circulate among large audience before it is ready.2-Not everything is a contribution. Youtube comments for example are not. If attempting to contribute to a project, consider rising the form of you presentation to that of the originator. If suggesting improvement to a schematic - draw and submit a schematic. If it is a video - consider doing a video. Internet is big, a single forum post is too easy to loose.

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 11:40:57 am
content: Quote from: HAL-42b on January 20, 2012, 11:20:10 amYes, it didn't work out that great, and I wouldn't recommend the approach to others. The amount of feedback is very hard to keep up with. And as always, and even more so with an actual hardware project, it is literally imposable to please everyone.I never really wanted to "social engineer" it, just shoot some commentary as I went along, as I thought it might make some interesting videos.But I guess a ton of feedback in every direction was inevitable.QuoteWell, if I've goofed something then by all means point it out by any available method, and that is a valuable contribution. But it's quite common that I can miss posts and comments.The real problem lies in that so many people don't comprehend the entire project and any compromises or personal preferences made, they just want their pet feature or device implemented at any cost. Nothing inherently wrong with that of course, that's human nature, but it gets a bit tired when the 50th person asks why I didn't use XXXXX microDave.

author: firewalker
author_rank: Super Contributor
timestamp: January 20, 2012, 11:45:20 am
content: Quote from: HAL-42b on January 20, 2012, 11:20:10 amRichard M. Stallman the GNU daddy (GPL licenses e.t.c.) did exactly that when he was developing gcc and other GNU programs.Alexander.

author: jnd
author_rank: Regular Contributor
timestamp: January 20, 2012, 11:47:58 am
content: What about using single 16-bitMCP23017expander instead of two 8-bit chips? You can save some space and cost too.

author: Psi
author_rank: Super Contributor
timestamp: January 20, 2012, 11:53:00 am
content: The new RGB led control for the LCD is nice. It could be quite useful to show output current.That way you'd probably notice if your circuit started to over current even if you weren't looking directly at the powersupply.Maybe something likeBlue = 0-33% of current limitGreen = 34-66% of current limitRed = 67-99% of current limitFlashing Red = current limit activeOr even mix them together and have the full 24bit color range.So many options when you have a MCU in the mix

author: Stephen Hill
author_rank: Regular Contributor
timestamp: January 20, 2012, 12:29:49 pm
content: This might be a direct question for Dave but others can feel free to chip in:I'm curious if there is any advantage or disadvantage in using a Transistor rather than an Optocoupler like a PC817 when stepping down the VSET voltage to limit the current (Q2 2N3904)?I'm designing a similar Dave inspired power supply and I've been switching between using a Tran and an Opto. In the simulation there doesn't seen to be any difference. So would there be any difference between the two in a real circuit or is it simply a matter of cost and simplicity?Any advice would be greatly appreciated.CheersStephenNB: I hope that made sense...

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 12:44:51 pm
content: Quote from: Stephen Hill on January 20, 2012, 12:29:49 pmOff hand I can't think of any benefit of using an opto-coupler for that part?There should be no effective difference, as you are simply servoing the SET pin to ground in either case based on the feedback. Whether the transistor is controlled via direct supply referenced base current, or base current via a LED shining on it, it should not matter.There might possibly be some difference in loop response or something though?Dave.

author: deephaven
author_rank: Frequent Contributor
timestamp: January 20, 2012, 12:53:14 pm
content: Dave, I really hope the various forms of feedback don't put you off doing further projects in exactly the same was as this power suppy. Your series of videos discussing your thought processes regarding the architecture of the design, chip type considerations etc is extremely educational to a lot of people. It also means that feedback can sometimes flag up the odd mistake. This is invaluable as you effectively have a team of people checking your design. I wish I had that to stop my mistakes before they get commited to a layout! So, you can receive this sea of comments from it's various sources, grab any useful ones and ignore any which you don't think are relevant to your thinking.

author: Stephen Hill
author_rank: Regular Contributor
timestamp: January 20, 2012, 01:13:05 pm
content: Thanks for the direct response Dave. This is what makes the EEVBlog and it's forum such a great place to be. It's also after midnight over there and your still up! Beautiful!

author: Unknown
author_rank: Unknown
timestamp: January 20, 2012, 01:14:45 pm
content: Quote from: deephaven on January 20, 2012, 12:53:14 pmHere lies the difference between a greenhorn and a seasoned designer in any field, including electronics. The seasoned designer is capable of spotting his mistakes in due course. Watching over his shoulder and pointing a finger on mistakes is unlikely to improve things. Sooner or later the experienced designer will spot his mistake and correct it without anyone's help. Trying to correct him prematurely is more likely to annoy and distract. I am not saying that seasoned guys do not make mistakes, they do. However they are capable of spotting and fixing them. Greenhorns like you and me on the other hand can benefit from a more experienced person watching over their shoulder and pointing at the mistakes as they are made. It prevents us from building on flawed ideas, this is one way of learning.

author: baljemmett
author_rank: Unknown
timestamp: January 20, 2012, 01:19:49 pm
content: Quote from: deephaven on January 20, 2012, 12:53:14 pmVery much seconded on this; I've really enjoyed this series of videos, and the really nice thing about seeing it progress from basic principles up to the full design is being able to say "well, if I don't like what it ends up being, I can go back to an earlier stage in the design and take it in my own direction". I'm waiting for the finished product and the mysterious 'higher purpose' to be revealed before I decide about buying the kit, but I might build up one of the earlier designs just for the experience anyway!

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 20, 2012, 01:32:31 pm
content: Quote from: HAL-42b on January 20, 2012, 01:14:45 pmone thing most "seasoned engineer" is lacking imho... ie to implement new and novel approach, such as touchscreen ipod like PSU

author: Bored@Work
author_rank: Super Contributor
timestamp: January 20, 2012, 02:00:17 pm
content: Quote from: HAL-42b on January 20, 2012, 01:14:45 pmDo you think Dave would have figured out the RESET blunder he is now playing down, on his own in reasonable time? Or don't you think it would have cost him at least one more respin of the PCB? I think if no one told him it would have cost him a good bunch of time to figure it out, and a respin.

author: thomastheo
author_rank: Regular Contributor
timestamp: January 20, 2012, 02:34:40 pm
content: This series on the power supply build is what pulled me into the eevblog and its forum, and i have to say it has been very interesting to see the build from start to finish, with Dave's work process and all. I've learned a lot from these videos, thank you! I can understand having your every move scrutinized along the way by a thousand eyes can be daunting, and it's easy to forget that while we are sitting at home commenting, you are doing all the actual work for usPlease continue doing what you're doing, and great work.with thanks,Thomas.

author: Royce
author_rank: Contributor
timestamp: January 20, 2012, 03:23:46 pm
content: I'm here from the Internet Design Review Committee! You may have though that by quitting the corporate world you could get away from The Committee, but you were wrong, Dave. Very, Wrong.But seriously, don't take us too seriously. I think these power supply videos have been an awesome series of videos that show the design process of a pro. I think they are quite valuable and I really hope you do more like them.

author: Unknown
author_rank: Unknown
timestamp: January 20, 2012, 03:25:19 pm
content: Quote from: BoredAtWork on January 20, 2012, 02:00:17 pmShould have said "A bunch of greenhorns watching over his shoulder...." I know very well that you are not a greenhorn btw.The issue of the reset pin is beyond me to be honest. If I had to do it myself I would have to learn as I go, probably by asking questions on this forum.Which brings me to why you shouldn't be bitter for not receiving recognition for your suggestion. There is a lot of valuable info on this forum but there is a lot of crap as well. Without winding it too long, if Einstein wrote his famous formula on a toilet wall nobody would have recognized him for it. So the method of delivery matters. This is why I maintain that one needs to deliver important critique in a manner more distinguishable from the background noise. Yes I am learning a lot on this forum, but If you ask me from whom I learned a particular thing I would shrug my shoulders.Besides, you've got balloons!...from what could only be Jeri if I judge by the method of delivery.

author: IanB
author_rank: Super Contributor
timestamp: January 20, 2012, 03:31:57 pm
content: Quote from: EEVblog on January 20, 2012, 09:16:36 amIMHO, this is the way it tends to go with any reasonably non-trivial design project.I think your sharing of the design process has produced very educational content. You may not want to do it again, but doing it this time should not be regretted.

author: ColinA
author_rank: Contributor
timestamp: January 20, 2012, 04:39:26 pm
content: Just want to give Dave a thumbs on the design. This is a great looking open source project with lots of potential. I cannot wait to get one in my hands and see what others do with it.I read a couple comments about an ethernet option. I have one of these and it is a quick way to get ur project on a network. Write a processing app and away one goes...http://www.wiznet.co.kr/Sub_Modules/en/product/Product_Detail.asp?cate1=5&cate2=42&cate3=0&pid=1161

author: elCap
author_rank: Regular Contributor
timestamp: January 20, 2012, 04:49:29 pm
content: I also must say I'm really enjoying this series of videos. I can understand that all the feedback can be difficult and overwhelming, but of course also very good and useful.For a future development video series (because I really hope there will be more) a method for handling feedback might have to be implemented. Something simple but effective.Maybe feedback can only be given by registered people in one dedicated thread (i.e. a sort of filter). All feedback have to follow the specifications (if outside specification --> ignore, or start a new project with new specifications). There should be a someone (external, not the main designer) handling and cleaning up among all the suggestions.

author: robrenz
author_rank: Super Contributor
timestamp: January 20, 2012, 05:51:51 pm
content: Hi Dave,I think you should start the sign up list for the power supply kit now. Just like the ucurrent list, it would give you an idea of what to make on your first run. This would cut down on all the whining you will get when the power supply kits sell out in the first 14 hours.I want 2robrenz

author: azrimola
author_rank: Contributor
timestamp: January 20, 2012, 09:10:07 pm
content: Dave, I don't really care about the details of the final version of the PSU.The real value is in being able to follow your design process and evolution of various ideas behind every little part of the PSU.Now, when the final version comes back from the assembly line, we expect a "Don't turn it on, take it apart video"

author: FreeThinker
author_rank: Frequent Contributor
timestamp: January 20, 2012, 09:10:20 pm
content: Hi DaveJust like to say I've enjoyed the videos so far mainly because of the none scripted approach as it gives an insight into the thought processes, and blind alleys you run into as a project 'matures'. However I think you would have saved yourself a lot of grief if you had explained to your viewers that this was the case ie an Adhoc project and not a step by step Tutorial (I hope I've explained myself clearly) also as commented elsewhere a dedicated feedback area would probably of helped too as people assumed that, because it was an open hardware project it was also a community design project, which it was not but they could suggest and discuss with other people and maybe have there ideas picked up, but at least feel involved and to have had there voice heard. Looking forward to the rest of the series keep it up

author: FreeThinker
author_rank: Frequent Contributor
timestamp: January 20, 2012, 09:20:25 pm
content: Quote from: azrimola on January 20, 2012, 09:10:07 pmExcellently put!! I have no need for such a comprehensive psu but find the design exciting and informative and am sure parts of it will be recycled in lesser projects in time to come.

author: quarks
author_rank: Frequent Contributor
timestamp: January 20, 2012, 09:42:29 pm
content: Hello Dave,the download link opens the older EEVblog #237 file.Regards MarcusPS: Now it works, thanks for the fix.

author: firewalker
author_rank: Super Contributor
timestamp: January 20, 2012, 10:06:47 pm
content: Try this link .http://www.eevblog.com/uploads/uSupplyBenchRevB.pdfAlexander.Quote from: quarks on January 20, 2012, 09:42:29 pm

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 10:12:33 pm
content: Quote from: HAL-42b on January 20, 2012, 01:14:45 pmWhilst it's true I'm going to eventually find my mistakes, I don't mind people pointing out genuine mistakes at all.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 10:15:58 pm
content: Quote from: BoredAtWork on January 20, 2012, 02:00:17 pmIn what way am I "playing down" the Reset oversight?I just did a whole video and redesign that used that issue as the basis.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 10:24:38 pm
content: Quote from: ColinA on January 20, 2012, 04:39:26 pmYes, these Wiznet modules are nice, and better than the Arduino shield IMO (and cheaper, at least at the original version level).I think I have one lying around somewhere.Looks like they have Arduino software support too on the download page.And a module of this size can maybe just fit into my existing case.Dave.

author: FrankT
author_rank: Regular Contributor
timestamp: January 20, 2012, 10:57:55 pm
content: A couple of noob questions and observations...* As asked a few times, is there any technical reason you chose not to multiplex the SPI programming lines? If not used as a shared SPI bus, the encoders could have been put on these lines. From what you said in the video, you are going to support the serial bootloader, so it will probably not be used much after your development.* You are using OC0A/OC0B/OC1A for the RGB which means you are using 2 of the 3 timers, leaving 1 8-bit timer.

author: ejeffrey
author_rank: Super Contributor
timestamp: January 20, 2012, 11:10:53 pm
content: Quote from: FrankT on January 20, 2012, 10:57:55 pmYou still wouldn't want to mutiplex the encoders with the hardware SPI/ISP lines, as that would interfere with programming -- the encoders provide an output signal and are not easily disabled / tristated during programming. I don't see any technical reason Dave couldn't have used the hardware SPI for the DAC/ADC and shared those pins with the ISP. All SPI slaves must leave all pins (including slave data out) high impedance when not selected. However, I haven't read the data sheet in detail, possibly there is some issue with the programming voltages present.

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 11:21:02 pm
content: Quote from: FrankT on January 20, 2012, 10:57:55 pmI left the hardware SPI lines lines free so they could be used by an external interface device, like Ethernet board, or other serial type comms device.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 20, 2012, 11:27:34 pm
content: I found my Wiznet module. It's the older one with the 2mm dual row header.The (newer?) WIZ820io seems to be less popular, but it's the go, with 0.1" pitch and a much smaller footprint.Will have to get one.need to look into the details of exactly what pins are required though.In either case it's not going to fit on the board (for back panel access), as it fouls one of the mounting screws.I guess I could always lave that mounting screw out and rely on the 3 others.Or mount elsewhere internally and have the run the cable inside...Dave.

author: baljemmett
author_rank: Unknown
timestamp: January 20, 2012, 11:29:32 pm
content: Quote from: quarks on January 20, 2012, 09:42:29 pmArgh - you're right - I just tried to watch 238 from my media server (which grabs the videos from RSS) and although the filename's right, the contents are the Makerbot unboxing video. Time to find out if the new television's "play from YouTube" works, I guess!

author: Psi
author_rank: Super Contributor
timestamp: January 20, 2012, 11:47:22 pm
content: Quote from: FrankT on January 20, 2012, 10:57:55 pmAnyone can modify the code to drive those pins as general outputs instead of output compare. The leds can easily be PWMed in software using just one timer if needed.Using the output compare pins just means people can use OCA functionally if they want.So using those pins gains optional OCA ability without any costFor example, if someone decided they wanted to do IR communication and replace one of the leds with a IR led then they would be very glad that OCA was available.Typical 36-44khz IR carrier frequency is much easier in hardware using an output compare.Its all about future proofing

author: reagle
author_rank: Unknown
timestamp: January 21, 2012, 12:44:13 am
content: Re "Reset blunder". Worst case Dave would've cut a few traces and added a few blue wires, in the process figuring out that on that particular micro that was not a good idea. It's not really a requirement that everything comes up perfectly the first time- no learning happens then. When dealing with relatively simple boards and working on one's own schedule, that's very minor. Now, if that was a 12 layer monster and customers were screaming at the door for delivery ...Edit: noticed another thing- ADC VIN seems to be missing a cap for low pass filtering before ADC. All the other signals are filtered

author: ColinA
author_rank: Contributor
timestamp: January 21, 2012, 03:09:22 am
content: Quote from: EEVblog on January 20, 2012, 11:27:34 pmYes it's new, I received as a sample. Was unable to find it for purchase back in November and was told it wasn't available for purchase yet.Works great and easy to use.

author: PeteInTexas
author_rank: Frequent Contributor
timestamp: January 21, 2012, 05:16:39 am
content: I'm all for gilding the lily but can't help the feeling a shark has been jumped. A "cascade of decisions" necessitated two more chips for want of a reset pin!?Come on now. Is ISPreallynecessary? The micro is not tasked for general purpose i/o. The pins are connected to specific functionality and so it is unlikely that programming the micro off-board will pose a great inconvenience. Besides, its probably a good idea to put the micro in a socket seeing as its in a power supply.And what's with capitulating on that protection diode? There was a video done specifically to show it was not needed.

author: Psi
author_rank: Super Contributor
timestamp: January 21, 2012, 05:40:00 am
content: Quote from: PeteInTexas on January 21, 2012, 05:16:39 amIt was more than that, adding the extra IO chips meant the lcd RGB backlight could be used, which will be useful.It also added spare IO which is very important for people wanted to add extra features.Quote from: PeteInTexas on January 21, 2012, 05:16:39 amYes. ISP is very important. It's a nightmare having to keep removing a MCU 20 times every hour for reprogramming while you code and test new features.Quote from: PeteInTexas on January 21, 2012, 05:16:39 amYeah, but some people wanted to have it anyway, might as well add space on the PCB for it.Keeps everyone happy then.

author: EEVblog
author_rank: Unknown
timestamp: January 21, 2012, 05:44:41 am
content: Quote from: PeteInTexas on January 21, 2012, 05:16:39 amYes, that's how it works. Basic math.All the pins are used, and you need to free up a pin, what do you do? You either compromise on or-rejig features somehow, or you gain yourself extra I/O somehow.That extra pin isn't going to magically appear.Yes, I could have used an ADC input to monitor multiple switches. Yes, I could have forgot about the RGB LED's, or extra switch input capability, Ethernet/serial capability, or.... Yes, I could have done this or done that. But I didn't, I did what I wanted to do.The only shark I've jumped is the one in your imagination.QuoteThis is an open source project, the ability to do ISP may be very handy for a lot of people, including myself.QuoteSome people may want it.People might use this board for other purposes than intended.Dave.

author: Zad
author_rank: Super Contributor
timestamp: January 21, 2012, 06:36:10 am
content: I think some people are missing the point. The point in this case is not the final product, but the development process. The journey rather than the destination. In electronics, the journey isn't a straight line, it frequently doubles back on itself and can entail returning to the start several times!I wouldn't have done it the same way either, but then I'm not making it. Get two engineers together and you'll get two vigorously argued opinions about how to do something. Keep them together for more than five minutes and you'll get another two - probably more. It is tempting to think of electronics as a pure science. It just isn't. It is the art of compromise and judgement. Change one trade-off even slightly, and everything can be screwed up.One thing that I would have done in this case would have been to prototype it on breadboard, and got some test software written. However, this wouldn't have been an issue if Itead had got their fingers out and got the PCBs shipped!On a more constructive note - How about using 1 or more of the spare outputs (or reconfigured inputs) to strobe the key switches. This would open the opportunity to have more keys for a 0-9 keypad etc via additional strobes. It would complicate the software, but it can still be interrupt driven.I wouldn't have specified Ethernet either, and would also have gone with RS232. Much easier to integrate with existing software and easier to hack some software together. But hey, if the SPI bus is available and there is a cheap module - why not? Leave it to the people in the open software community, it all adds to number of potential purchasers!To clarify something I said in an earlier post; I wasn't intending that the PSU actually be an Arduino, but be a "shield", with the Arduino supplying the processing (and external brick power supply). I know this is ridiculous, but we have seen recently with the Quadcopter and Makerbot, that people just love buying "stuff" to plug into their Arduinos, even if it would be cheaper as a standalone unit with integrated controller. Places like Adafruit and Sparkfun will gladly stock a shield, whereas they would not want to stock yet another Arduino clone itself. Just a thought.Of course, as it is an open design, a shield version could be designed at a later date anyway.

author: PeteInTexas
author_rank: Frequent Contributor
timestamp: January 21, 2012, 07:21:51 am
content: Quote from: EEVblog on January 21, 2012, 05:44:41 amDid that reset pin really need to drive the LED? Is that LED really needed? Isn't there an LCD already? Was finding screen real estate more costly than adding two more chips?QuoteDid I catch it in the video that the micro will do the boot loader serial comm thing? What's the difference. Well, if I remember right you can't program fuses with the boot loader. How often does fuse programming come into play? 20 times an hour seems ridiculous to me and not worth the pins.QuoteQuite frankly I'm disappointed. I know that means nothing to you and thats fine. But I've seen a lot of your videos plus a lot of the Amp Hour and its always this "design by committees are bad", bureaucracy is bad, dilbert this and dilbert that and I ate it all up. But then what did you go on and do? Gave in to pointy headed bosses online even after you went to the trouble of video to show them wrong. Maybe I was expecting too much.And as far as "people might use this board for other purposes", thats a cop out. Just because its open does not mean you have to put in the kitchen sink.just my two measly cents

author: Psi
author_rank: Super Contributor
timestamp: January 21, 2012, 07:34:47 am
content: It's not being "designed by committee" at all.It's being designed by Dave and he's free to accept or reject suggestions people have.In "Designed by committee" no one person has final say.The video only showed that the circuit appears to work without the diode.Even after testing, any experienced engineer would include a footprint on the pcb just in case it turned out to be needed later on. After all, it doesn't cost anything to add 2 extra tracks/holes to a pcb.

author: EEVblog
author_rank: Unknown
timestamp: January 21, 2012, 08:24:54 am
content: Quote from: PeteInTexas on January 21, 2012, 07:21:51 amIt's want I WANTED. I know that might be hard for some people to understand, but try, please.If you want something different, go design your own.QuoteIt can do both.Some people may want the bootloader, just like a regular Ardunio, to use their existing tools and the Arduino interface as they are used to. Others (like me) might like a direct ISP interface using an external programmer for development and debugging using any tool they like. In any case the ISP pins are already freed up for the Ethernet/serial interface, so you get that for FREE.Both are useful for troubleshooting.I wanted both, I catered for both, end of story.QuoteCorrect. Because if I cared what every single person thought about every aspect of any one of my videos, I'd end "doing a photonic induction". Seriously, I would have to quit the whole damn thing.So why don't you just quit it with the unproductive comments? I don't need it.QuoteAdding a footprint for a diode that might very well be useful for some scenario's is not "putting in the kitchen sink", or giving in to anyone, or a "cop out".My testing was not extensive, nor was my conclusion from what little testing I did. It's simply an additional footprint I put in because it might turn out to be worthwhile in some circumstances.Dave.

author: Rerouter
author_rank: Super Contributor
timestamp: January 21, 2012, 08:44:09 am
content: great work as usual dave, to peteintexas, this kit has always been something with a purpose, where dave was nice enough to make it easy for us to mod, and by releasing the schematics able for us to completly redisign it if we wish,love your choice of the MCP23008-E/P, means we any mix of up to 8 inputs / outputs, and that they can be used to run leds directly, being how they are clamped to 20mA

author: quarks
author_rank: Frequent Contributor
timestamp: January 21, 2012, 11:45:52 am
content: now it is fixedQuote from: quarks on January 20, 2012, 09:42:29 pmArgh - you're right - I just tried to watch 238 from my media server (which grabs the videos from RSS) and although the filename's right, the contents are the Makerbot unboxing video. Time to find out if the new television's "play from YouTube" works, I guess!

author: djsb
author_rank: Super Contributor
timestamp: January 21, 2012, 12:29:00 pm
content: Will there be a revision C schematic? Is the design frozen at this stage? If so, I may volunteer to create a multi page schematic (Altium designer based) if that would be useful? It may take a few weeks though as I'm still learning how to use AD10. It will also give me a chance to get some practice. Please let me know if this would be a useful contribution.David.

author: EEVblog
author_rank: Unknown
timestamp: January 21, 2012, 12:48:07 pm
content: Quote from: djsb on January 21, 2012, 12:29:00 pmThanks, but I'm not after a multi-page schematic. I prefer the single page version.There's always room for a Rev C!But the PCB has been ordered for Rev BDave.

author: thilo
author_rank: Regular Contributor
timestamp: January 21, 2012, 12:54:35 pm
content: Quote from: djsb on January 21, 2012, 12:29:00 pmFor an open source project that's hardly useful, because the schematics should not only be available as a PDF, but also as project files for a CAD program that many people have access to

author: djsb
author_rank: Super Contributor
timestamp: January 21, 2012, 01:08:42 pm
content: OK then, If I did a version using Kicad would you provide that for download on your site Dave?David.P.S I'm not going to put in the effort if there is no demand for KiCAD project files and unless they can be shared with the community.

author: RJSC
author_rank: Regular Contributor
timestamp: January 21, 2012, 02:43:54 pm
content: I don't want to bug you with the "hi, please implement my feature" talk, I can mod to my own needs, but I want to ask you:Is there anything against using I2C DAC and ADC?Why have yet another bus and more used pins?Since the feedback loop is in the LT3080 itself, the is no need to have super fast DAC and ADC communication with the minimal possible latency.Having only one bus would simplify PCB routing (especially to people who are doing the PCB them selfs at home and you most definitely will like to do it single sided, not so much for Dave who will have them made at a fabhouse and probably double sided anyway).I have seen power supplies where the feedback loop is implemented in the microcontroller driving a transistor directly, but since it's not the case, do you see any problems with using an I2C ADC and DAC?

author: EEVblog
author_rank: Unknown
timestamp: January 21, 2012, 10:10:34 pm
content: Quote from: thilo on January 21, 2012, 12:54:35 pmI used Altium for this project, and that's what format the files are in.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 21, 2012, 10:11:49 pm
content: Quote from: RJSC on January 21, 2012, 02:43:54 pmThe SPI ones were cheaper.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 21, 2012, 10:17:47 pm
content: Quote from: djsb on January 21, 2012, 01:08:42 pmSure, no problem.Dave.

author: metalphreak
author_rank: Frequent Contributor
timestamp: January 22, 2012, 04:10:53 am
content: There's a difference between "Open Source" and doing all the work for youRecreating the PDF schematic in whatever CAD software you use isn't that difficult, and it encourages you to fully understand the circuit you are building, rather than just copy/paste and lay out a PCB. Open Source is about encouraging learning, innovation, and sharing, not tailoring free designs to each individuals needs and wants. Dave has done a wonderful job explaining how each part of his design works, which provides a fantastic base for you to build upon adding any extra features or specs you require.If you do end up recreating it in KiCAD or Eagle for your own purposes then it will be greatly appreciated if you do share it

author: Janaha
author_rank: Newbie
timestamp: January 22, 2012, 08:39:23 pm
content: Hy Folks, hy Dave,i just want to say that i realy realy like the Power Supply series of videos. For me it's the first series of videos where not only an already made laboratory power supply is presenet to the public. It's the first show, where someone shows off all the details of his design desicions. And not only this, he makes it also so that it's understandable by someone like me, who only does some elektronic designs with microcontrollers as a hobbyist.Power supply design just seemed to be the holy grail of electronics desings to me. Here in germany we have a german forum calledwww.microcontroller.net. I have seen so many posts there where some guy just kindly presented a power supply design as open source and got almost instantly flamed with a ton of negative posts, for what he did wrong in his design. But there never was a guy who showed how to make it right. And no one has the power supply that pleases all their desires.So i want to say, keep up the good work. And many thanks for all the information and the very good presentation.Janaha

author: Zad
author_rank: Super Contributor
timestamp: January 22, 2012, 09:14:23 pm
content: Quote from: EEVblog on January 21, 2012, 12:48:07 pmAs an aside, this reminds me of one of my pet annoyances. Designers (or, more likely, design department rules and guidelines) who put one IC or a handful of passive components on one sheet, and then group all the signals together into buses. CAD tools and abstraction concepts are great, but it can be taken too far. An engineer should be able to see the interconnections at a glance.If it gets too complicated for 1 sheet, I tend to split it into analogue + digital. That doesn't disturb the visual flow too badly.

author: PeteInTexas
author_rank: Frequent Contributor
timestamp: January 23, 2012, 05:46:14 am
content: Quote from: EEVblog on January 21, 2012, 08:24:54 amYes, of course. So sorry. Being from Texas I shoot from the hip a lot in speaking my mind. But you're right.And yes, I will be forking your design for myself. I'll take everything after the DAC and before the ADC in rev A and hook it up to one of those duino thingys. Knowing me, this will get done by 2025.QuoteNo, no, no, nooooo! you're right, you're right! Just don't pull a photonic induction on us.

author: enz
author_rank: Regular Contributor
timestamp: January 23, 2012, 01:39:30 pm
content: Quote from: EEVblog on January 21, 2012, 12:48:07 pmHi Dave,i don't know if someone mentioned this already, but i think you will really need a Rev C.I just had a closer look to the Rev B schematic and i think you accidentally swapped the inputs of the current-control Opamp (U3B), in Rev A this seems to be correct.MartinEdit: typo removed

author: senso
author_rank: Frequent Contributor
timestamp: January 23, 2012, 10:18:41 pm
content: If you dont mind I will start to copy this schematic to Eagle but use an Atmega644p, to have more voltage swing, maybe in the 15/18v range all I need to do is have some more gain in the voltage op-amp?

author: MickM
author_rank: Regular Contributor
timestamp: January 24, 2012, 01:30:51 am
content: Hi Dave;I want to tell you how cool it is to watch a pro design something.The decisions,and reasons why are very interesting.I have learned a lot from watching your videos.Have you decided how to sell them?Bare PCB, PCB and a Bag-O-Parts, PCB with SMD installed, fully built and tested PCB, fully built and tested unit.I would go for PCB + Bag-O-Parts.Just a warning - you showed your Philips frequency counter.I have the PM6671.So I pulled it out and it was a bit dusty (no front cover).I wiped it down with regular rubbing alcohol (91% Isopropyl) - and the lettering started to smear.Arrgh!! alcohol soluble paint - who knew!.So now you are warned.MickM (Seattle)

author: Shale
author_rank: Contributor
timestamp: January 24, 2012, 02:04:36 am
content: Hi dave. First post here. I have watched several of your videos and I am learning a lot. I like how you are doing this set of videos. I am learning about how and why you are making design decisions. I am very new to electronics and I do not know what everything is by any stretch but thats what google is for. Im sure it can be a pain in the tail with some people complaining about things, but I would like it if you did more builds like you are doing this one.

author: amspire
author_rank: Super Contributor
timestamp: January 24, 2012, 02:07:34 am
content: Quote from: senso on January 23, 2012, 10:18:41 pmYou can increase the output voltage if you lower the current. You do not want the regulator IC going into thermal current limiting as you will start to get different output current limits to the one you have set.At a current of 1A maximum, the maximum practical output is something like 10 -12 Volts. Reduce the current to 0.5A and you could increase the output to 20V with something like a 24V source for the supply.Richard.

author: BravoV
author_rank: Super Contributor
timestamp: January 24, 2012, 03:22:55 am
content: Codename Platypus ??

author: mobbarley
author_rank: Regular Contributor
timestamp: January 24, 2012, 03:30:11 am
content: Just saw that on twitter - nice sneak peak

author: Nick Gammon
author_rank: Contributor
timestamp: January 24, 2012, 06:22:42 am
content: Dave,You really inspired me (in earlier videos) to get back into electronics after a lengthy break. Thank you very much!Your videos about the power supply show clearly the sort of things that happen to a designer during the design process. Sometimes you can get half or three-quarters of the way through and realize you need to make major changes. That is normal, and you show how it happens.Personally I don't care if the final version has Ethernet, Bluetooth, infrared remote or motion-sensing capabilities. The important thing is the knowledge you are imparting about design decisions. Knowledge we can all take with us to improve our own processes.Remember: "A camel is a horse designed by a committee".

author: ronwoch
author_rank: Contributor
timestamp: January 24, 2012, 07:02:45 am
content: Just want to add to the chorus of voices saying thanks for letting us inside your head as you build this project! I am looking forward to the 'big reveal' as to what you have in mind, specifically, for this design.Hoping the kits will be available around the time that my tax return is!Again, thanks for all you do Dave, it inspires everyone here. (Or else they shouldn't be here)

author: sonicj
author_rank: Frequent Contributor
timestamp: January 24, 2012, 01:36:58 pm
content: scaled & tiled for US letter x 4

author: krivx
author_rank: Frequent Contributor
timestamp: January 24, 2012, 02:21:53 pm
content: Is it too early to ask about pricing for kits?

author: FreeThinker
author_rank: Frequent Contributor
timestamp: January 24, 2012, 02:32:29 pm
content: I Think Dave was aiming at around $100 or so .... But that was Yesterdayhttps://www.eevblog.com/forum/index.php?topic=6497.msg85141#msg85141

author: krivx
author_rank: Frequent Contributor
timestamp: January 24, 2012, 03:22:01 pm
content: That seems very reasonable, I'm looking forward to it now.

author: senso
author_rank: Frequent Contributor
timestamp: January 24, 2012, 04:13:47 pm
content: Thanks for the information Amspire, I will settle with the standart 10v version as it is enough to do electronics works, motors and powerfull things dont need a super precise power supply, but I have one question is there any substitute for the MAX4239ASA+, Mouser doesn't carry it and Maxim wants me to sign some strange contract to send me two samples of that chip, and I don't like to sign things that are under the USA laws..

author: EEVblog
author_rank: Unknown
timestamp: January 25, 2012, 12:02:42 am
content: Quote from: FreeThinker on January 24, 2012, 02:32:29 pmNo firm price yet, but I'm pretty darn sure that I won't be able to get it under $100, just based on the parts cost.It could very well be higher as I haven't yet factored in time for me to kit these things up, or pay someone else to kit them up.Dave.