uSupply USB - Snap Poll! - Page 1
Forum section: electronics / projects

author: EEVblog
author_rank: Unknown
timestamp: January 10, 2013, 10:46:27 pm
content: Laying out the next version of the "USB" uSupply now.As the title says, should such a small and low powered battery powered USB supply bother having serial comms capability via USB?I know it would be kinda cool to have PC control, but without including it, the micro is 2/3rd's cheaper (due to lower pin count package saving), and no need for the optocouplers etc. How many people would actually want to PC control a little rechargable PSU? (Any bench version would definitely have it of course)Still need isolation for the USB charging though, so I know what people are thinking - it has a USB connector, it has power isolation, so why not include comms as well?NOTE: I am not talking about the bench version of the uSupply, this is the smaller pocket size USB charging version.Many will be happy to know the latest design has dual LED displays and dual knobs like on old proto I have showed off. And uses an 18650 battery.Dave.

author: JoannaK
author_rank: Frequent Contributor
timestamp: January 10, 2013, 10:52:17 pm
content: Whatever you choose, there will be

author: mdev
author_rank: Newbie
timestamp: January 10, 2013, 10:57:25 pm
content: maybe two versions: one without the serial, and one with serial but without user interface, ie, screen and knobs, intended to be used with a terminal

author: EEVblog
author_rank: Unknown
timestamp: January 10, 2013, 10:58:25 pm
content: Quote from: JoannaK on January 10, 2013, 10:52:17 pmAin't that the thruth!I'm the only one stupid enough to ask these thingsDave.

author: Torrentula
author_rank: Regular Contributor
timestamp: January 10, 2013, 11:00:42 pm
content: Quote from: JoannaK on January 10, 2013, 10:52:17 pmThat and I don't see the value it adds to the product if it's only charged by USB, plus it is really easier and faster to turn a knob and read a display directly on the supply instead of having to type long command strings into the terminal.It's a power supply, I want a voltage setting and a current limit setting and not remember bloody commandsMy two (hobbyist) cents,Elia

author: JoannaK
author_rank: Frequent Contributor
timestamp: January 10, 2013, 11:08:43 pm
content: Quote from: EEVblog on January 10, 2013, 10:58:25 pmNo. I'm quite sure a lot of us know the warm and fuzzy feeling.

author: Bored@Work
author_rank: Super Contributor
timestamp: January 10, 2013, 11:25:20 pm
content: There are advantages having a remote controllable PSU. E.g. logging current consumption of some device or driving a device with a particular voltage function.The thing is does the feature increase or at least not decrease the overall profit? To answer that you have to estimate. Are people willing to pay extra for that feature? If not, will the feature sell more PSUs, at reduced margin, but in total at more profit?I don't think the poll will answer such questions.

author: Smokey
author_rank: Super Contributor
timestamp: January 10, 2013, 11:32:34 pm
content: Put the footprints on the PCB but omit the parts for a cheaper version. You can even use super small more expensive parts since they won't be stuffed for the mass produced version. A lot of us are capable of soldering that in later if we want it.Or do a second plug in board with just header on the main board. This way you can go the big company "optional extra" and sell the communications board for 1/2 the price of the whole unit.

author: 8086
author_rank: Super Contributor
timestamp: January 10, 2013, 11:33:58 pm
content: How about a self upgrade option? Leave unpopulated footprints and provide a BOM for the serial part?

author: frank26080115
author_rank: Regular Contributor
timestamp: January 10, 2013, 11:38:50 pm
content: Personally, I've already started laying out a version of the uSupply but with a ATmega32U4, so it will have USB by default. This is just for myself for fun and learning.I plan on using serial commands to simulate a battery discharge curve, while logging current consumption. I need to characterize a SEPIC LED driver.I don't quite get how USB and optocouplers are related.Firmware update via bootloader is always welcome, I don't know how many times you'd need to do this for a simple power supply though.

author: Smokey
author_rank: Super Contributor
timestamp: January 10, 2013, 11:42:39 pm
content: Or how about just putting some IR LEDs on the UART. Make the spacing compatible with the cheapest adapter for some other commercial multimeter that has IR and you have a cheap option using an already existing IR-USB cable you don't have to design.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 10, 2013, 11:49:51 pm
content: The only reason I can see to have an interface is for firmware upgrades, and even then possibly margnal - ISTR the concept was a simple, small general-purpose PSU, not a whizz-bang networked jobby...After all It's just a ***ing power supply.....

author: Teemo
author_rank: Regular Contributor
timestamp: January 10, 2013, 11:51:02 pm
content: Quote from: EEVblog on January 10, 2013, 10:46:27 pmThis is really good news if two knobs are back, I like it!

author: EEVblog
author_rank: Unknown
timestamp: January 10, 2013, 11:56:23 pm
content: Quote from: Bored@Work on January 10, 2013, 11:25:20 pmAgreed.And therein lies the rub, I have no idea.All I know is that the cost of this thing has been creeping up and creeping up, which was against my original intention.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 11, 2013, 12:00:43 am
content: Quote from: mikeselectricstuff on January 10, 2013, 11:49:51 pmEven if I add serial comms, I have no intention of adding a bootloader to allow firmware update via USB.Dave.

author: opticpow
author_rank: Contributor
timestamp: January 11, 2013, 12:47:01 am
content: Quote from: EEVblog on January 11, 2013, 12:00:43 amEven though you're not adding the bootloader, someone else might being open and all. That said, I'd expect it on a bench supply, this maybe not so much. Would still be cool thoughExcuse me while I go extract the fence post

author: EEVblog
author_rank: Unknown
timestamp: January 11, 2013, 12:55:14 am
content: Quote from: Smokey on January 10, 2013, 11:42:39 pmThat's not a bad idea at all.But in the end, just saves a bit of cost on the chip.Basically, I'm paying almost 3x the cost on the micro by having serial interface. The cheap chip (ATtiny48/88) does not have a UART. The ATMEGA88 I was using does not have enough pins, so to go serial I'm forced to use the ATmega164ADave.

author: 8086
author_rank: Super Contributor
timestamp: January 11, 2013, 01:12:33 am
content: Software UART?

author: Lightages
author_rank: Unknown
timestamp: January 11, 2013, 01:25:08 am
content: Keep it simple and keep the cost low. The original intent was to have a simple to use, low power, handy power supply for random use in the field. If someone needs a power supply that will have all the bells and whistles then they would already have known the need and have a more capable supply ready.

author: EEVblog
author_rank: Unknown
timestamp: January 11, 2013, 01:35:46 am
content: Quote from: 8086 on January 11, 2013, 01:12:33 amUgly, but possible, if there were enough pins available...it's one of those project when you don't need much processor grunt, but pins count. So you are forced to pay for a more powerful chip in order to get the extra pinsDave.

author: mdev
author_rank: Newbie
timestamp: January 11, 2013, 01:37:34 am
content: or some header for RX and TX; whoever want to use the software interface can plug an USB to TTL interface; and may even use the Arduino digital pins 0 and 1 too, without the ATMEGA

author: Fsck
author_rank: Super Contributor
timestamp: January 11, 2013, 01:43:41 am
content: I think the poll might be inaccurate if the price difference isn't too large.

author: Spikee
author_rank: Frequent Contributor
timestamp: January 11, 2013, 01:53:34 am
content: Dave just make a header for the cheap PL2303 FTDI adapters from ebay. They are like 1.7 dollars each.Who wants serial buys one from ebay

author: EEVblog
author_rank: Unknown
timestamp: January 11, 2013, 02:02:10 am
content: Quote from: Spikee on January 11, 2013, 01:53:34 amNot quite that easy, they aren't isolated.The whole idea of this is to make it idiot proof by being isolated.I think I'll just go for the bigger micro and leave the serial footprints unpopulated.Dave.

author: Harvs
author_rank: Super Contributor
timestamp: January 11, 2013, 02:02:32 am
content: Quote from: frank26080115 on January 10, 2013, 11:38:50 pmI see no point of having a serial connection if it's not isolated from the supply output. That isolation is just needed too often in a lab power supply.Nope I don't really it being worth the cost, I'd never use the uSupply when in my lab, and I can't think of an application outside of the lab where I'd need PC control or data-logging. As stated already, the lab supply would be a totally different kettle of fish and some sort of PC control would be must for me.

author: mariush
author_rank: Super Contributor
timestamp: January 11, 2013, 02:02:56 am
content: By the time you actually finish this thing, it's going to be another year or two and several iterations so I'm voting yes, because it won't matter anyway.Also second reason, I think price won't be influenced much by the parts, you're probably going to send it to Sparkfun or Adafruit to sell them for you and they're going to add their own profit margin to the cost.A 6$ chip instead of a 2$ chip won't make much difference at the final cost.Wondering if you can somehow drop the isolation feature by using some solid state relays or something to disconnect output when user plugs something into the power jack. Maybe have the power connector behind a "door" that when opened disconnects the relays.Ignoring the "no isolation" problem - I know you want to have it isolated - would something like this be cheaper and would the tradeoff be worth it?Then, maybe leave a 2 pin connector on the board for people that are smart enough to buy a small isolation transformer and a 7805 chip to make a 5v power supply for the supply.

author: Harvs
author_rank: Super Contributor
timestamp: January 11, 2013, 02:23:12 am
content: A quick search on Digikey shows the cheapest uC with USB is a PIC16F1455 @ $1.30 in 100 Qty, and a SI8431AB-D-IS 3-channel isolator $1.41 in 100 Qty.So if you've got the board room, you may actually find the extra $3 in parts would significantly appeal to the broader Sparkfun type crowd (for some reason people just love being able to connect things, even if for no real practical purpose.) You can just imagine it now, "Turn your Raspberry Pi into a....".

author: Zad
author_rank: Super Contributor
timestamp: January 11, 2013, 05:03:32 am
content: I think you'd soon get sick of people saying "WTF this PSU has a USB connector, why can't I control it from my PC?" and then, as is the nature of Open Hardware, 3 days later someone comes out with a USB programmable version, and your product is now outdated, even if the new board is $5 more.It is a strange dilemma though. Would the price of the different micro have a big effect on the overall BoM and final retail price? I'm just imagining the situation where (for example) Adafruit have both products on a sales page, the simple standalone one with knobs and LED displays, next to the "headless" one with all the control done from the PC. Removing the displays etc has made the fancy programmable version cheaper than the barebones one.Personally, it seems to me that a lot of the hipsters and fashionistas that follow Sparkfun and Adafruit have no shortage of cash. They are, by and large, serial Apple buyers. I would go straight in with the top end machine, USB (serial) controllable, nice display. Then, as you see what the userbase feedback is, produce a v.2.

author: IanJ
author_rank: Unknown
timestamp: January 11, 2013, 06:50:32 am
content: Hi,Definitely no need for USB control..........just abide by that old KISS thing, and knowing full well you can always upgrade to a 2nd version later down the line.........folks that want it will buy the 2nd version.The bench version will/should have all the singing/dancing stuff.Ian.

author: kizzap
author_rank: Unknown
timestamp: January 11, 2013, 11:27:22 am
content: I voted No, purely because if it becomes computer controlled, it would mean that it is more likely to be fixed to a certain point and not as mobile as it could possibly be.Also if it were connected via usb, surely you would end up just using the usb Power instead of the battery...(Also First Post!)

author: Psi
author_rank: Super Contributor
timestamp: January 11, 2013, 11:57:46 am
content: na, i don't think it needs it.If possible leave some room/footprints on the PCB to make it easier to hack some comms in if people want.Don't bother spec'ing the parts for it if they're more expensive.I'm sure someone could hack up a software serial port using existing i/o pins if they really want comms.I doubt the extra feature would result in more sales.

author: lapm
author_rank: Frequent Contributor
timestamp: January 11, 2013, 03:46:00 pm
content: I voted No, basicly becouse it was originally inteded KISS princible inplementation of such power source. USB was there for easy powering and recharge of internal battery.Also im sure theres few readers/followers here that can comeup hardware/firmware modifications needed to implement such remote control features if they really really need it...Lets be aware of feature creep if we want Dave actually finnish this project in some sensible timeline.

author: frank26080115
author_rank: Regular Contributor
timestamp: January 11, 2013, 03:50:40 pm
content: I just did some research on isolating USB, it doesn't sound easy/cheap (optoisolators on two bidirectional data lines at 12Mbit/s? $$$$$$), the isolation needs to be done elsewhere, like on the UART line or I2C or SPI busses, which probably means the only way is to use another UART-to-USB IC with optoisolators on the UART lines, right?I'd say it's not worth the cost, but provide two pads for TX and RX so people can wire up things to it themselves. A footprint is free.

author: Zad
author_rank: Super Contributor
timestamp: January 11, 2013, 04:24:54 pm
content: Quote from: frank26080115 on January 11, 2013, 03:50:40 pmThis is exactly where it is done. The FTDI chip sits on the USB and provides a serial (UART) connection to the PSU controller on the "hot" side, which is isolated via the opto-isolators which only need to run at 115kbit/s or less. The core of the problem, as I understand it, is that to provide 2 UART pins on the controller requires the move to a more expensive controller.Optocouplers are 1.7 pence each at Farnell, so not really part of the price equation.

author: ejeffrey
author_rank: Super Contributor
timestamp: January 11, 2013, 04:34:52 pm
content: I voted yes because I think it is a reasonably useful feature, but I might revise that if I knew the overall cost.You could do what agilent does: add the serial port, don't raise the price, but charge a $50 license code for people who want to unlock it

author: Wytnucls
author_rank: Super Contributor
timestamp: January 11, 2013, 04:35:44 pm
content: Quote from: Lightages on January 11, 2013, 01:25:08 amMy thoughts, exactly.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 11, 2013, 04:36:21 pm
content: I would glady pay the extra money for PC control. I would pay 10$ + extra for it but I do see the counter argument of it being a field supply. Since this is a portable version then I think that you should leave it out.

author: BillyD
author_rank: Regular Contributor
timestamp: January 11, 2013, 04:54:08 pm
content: Hi. I voted no for these reasons:(a) if I understand correctly, the serial connection also adds the need to supply or support software for the host system. So software development + testing enters the equation with all the usual costs and responsibilities.(b) I've had numerous devices and gadgets down the years which connect to a USB, but those freebie data connections are invariably useless and I've never once continued to utilise it after the initial couple of hours poking around with it.(c) if you can plug in the USB cable without Windows trying (and usually failing) to identify the device and install drivers etc, then this is a good thing!Billy.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 11, 2013, 05:07:45 pm
content: If someone that has no other supplies (is used to using a 9v+lm317) then having a USB option would introduce them to more advanced lab techniques and allow their testing and design to be more sophisticated however I assume thats what the bench version is for.

author: Psi
author_rank: Super Contributor
timestamp: January 11, 2013, 08:15:21 pm
content: Could always use IRDA, that might be cheaper to implement as an unpopulated pcb option.Could be done in software at a later date and would only require an led + phototransistor footprint.Or simpler still, have a phototransistor + envelope filter footprint on the pcb. That way people could implement a simple IR remote style system in software to set voltages/currents remotely and it would only require 1 output line.

author: Smokey
author_rank: Super Contributor
timestamp: January 11, 2013, 08:40:17 pm
content: Think about it this way. In what situations are you really going to use a battery powered portable variable power supply?The main use I would see for something like that would actually be as a portable voltage/current source for applying signal voltage to some circuit input. Hang with me here.I guess I don't see the thing being that useful for actually supplying the main power for some project. If you are working on some new design you probably need other equipment that is already fixed on your bench like an oscilloscope and function generator, in which case you will be using your bench supply to power the project. It's not like you are going to drag all that stuff to the city park for a sunny debug session under the trees, however nice that may sound. Unless every piece of equipment you have is battery powered, the extension cord would trip all the joggers. Or the generator will wake up the neighbors. If the main development part of the project is already done, then it will already have it's own power source so you won't need to power it from a portable supply.Now what you might need to do is supply some signal voltage/current to test a circuit in the field or away from your bench, like an amplifier or something. A battery powered portable adjustable voltage source would be great for this. Assuming the output can swing negative as well, this would make a great replacement for a passive battery box and that would be super useful in the lab too. And while just being knob adjustable is probably enough, having a computer interface would be killer for creating sequences of test signal voltages. Especially if you are doing embedded stuff, you're never far from a laptop anyway.It's certainly a feature I'd pay more for since I can personally see uses for it in the context of a portable variable voltage/current source. If I only wanted to actually use it to supply main power for a project then I wouldn't care since the voltage probably isn't ever going to change once you set it up.I guess it comes down to what people are going to use it for.

author: EEVblog
author_rank: Unknown
timestamp: January 11, 2013, 10:10:26 pm
content: Quote from: frank26080115 on January 11, 2013, 03:50:40 pmCorrect, that's how I'm doing it.I think the best option is to use the bigger more expensive micro (it might come in handy) and leave the footprint in place for the FTDI and opto's for those that want their own serial solution.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 11, 2013, 10:13:33 pm
content: Quote from: Zad on January 11, 2013, 04:24:54 pmCorrect. The cheaper AVR chip does not have the UART, nor the two lines extra needed for serial (all pins used)The FTDI can also provide the USB negotiation for the 500mA current, for those who like to bitch about such things.QuoteI'm using 4N26S, the cheapest option available at Digikey. 13cents 1000off. If you have cheaper/better, I'm all ears.

author: EEVblog
author_rank: Unknown
timestamp: January 11, 2013, 10:16:39 pm
content: Quote from: BillyD on January 11, 2013, 04:54:08 pmAnother good reason to leave it unpopulated by default.If people want serial, they can add the chip and then get the beep every time they plug in to charge.Dave.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 11, 2013, 10:48:49 pm
content: Quote from: EEVblog on January 11, 2013, 10:16:39 pmCan you leave a jumper or switch footprint so people can choose weather or not they want the beep even if they add the chip?

author: JoannaK
author_rank: Frequent Contributor
timestamp: January 11, 2013, 11:13:56 pm
content: I did not comment the question at the beginning cause I think Dave knows the way I see this. As a Recap, I see two connected issues here: Should there be a data link and should there be an isolation at the Usb charge input?I understand that the idea of power isolation is nice safety feature, even though it obviously add cost and complexity of the board. At the same time there is the question why the battery-running power supply should be connected to a PC anyhow while it's operating, if there is no data connection.Besides, using Usb port+connector just to charge the device is somewhat questionable idea. Even though the standards are quite often ignored, the Usb -client should do proper negotiating before trying to suck considerable amounts of power from the host. With wall-warts this is not an issue, but Laptops can be a bit sensitive of this since this power stealing does cause considerable loss of run time.For the data link, I think that it adds a considerable value for the product and opens up possibilities finding new uses for the device. I have no idea if Dave would be willing to spend lots of time doing PC/tablet software for this project, but considering this power supply becoming OpenHardware I'd expect someone be willing to take the post.But in the end. I decided to vote that I'm not interested. And that's mainly cause I don't need this kind of power supply and my estimation of the end-user price is too high for me to purchase this as a support site/Dave.

author: silicon_ghost
author_rank: Contributor
timestamp: January 11, 2013, 11:41:44 pm
content: I voted no. This is driving up the cost and complexity a bit too far with feature creep.On the other hand, I would expect USB/Serial PC control on the benchtop edition of the EEVBlog power supply.

author: Teemo
author_rank: Regular Contributor
timestamp: January 16, 2013, 11:08:06 am
content: Hi.I think having PC control for is not very important for user interface.But I read Microchip's Application library for usb microcontrollers. There is special example for usb chargers. It says charger must register itself to the PC if it draws more than 100mA. So if this is the case usb data connection must physically be there anyway, to check the device in.When the device is registered it can draw 500mA.Also about USB -- it might be good idea to add detection for apple chargers. You can't draw more than 500 mA from regular USB connection. But if device can detect connection to Apple charger, it can draw up to 1A out of it. Detection based on the resistors in Apple charger's data lines, as Ladyada describes in her page.