Solder Buddy PCB - Page 1
Forum section: electronics / projects

author: unknowndomain
author_rank: Regular Contributor
timestamp: January 03, 2014, 05:04:56 pm
content: Some of you may have seen the brilliantSolder Buddyproject byJude Pullenlast year. I am working on building my own one, and wanted to make the circuitry into a simple through hole PCB.I am not very experienced and would love a bit of a sanity check before I build the circuit up on breadboard.The first image is just voltage regulation and a power LED, the 9V VIN will go into two power regulators, one 5V and one 6V for the motor. I should probably add a power switch...UPDATED: 03:11 4/1/2014The second sheet is a 555 PWM/Potentiometer circuit that outputs into a L293 H-Bridge enable pin, there is a direction switch which sends 5V to one pin, whilst the other is held down by a pull down resistor to ground. I think this will work?UPDATED: 03:11 4/1/2014All help/advice appreciated!

author: Alana
author_rank: Frequent Contributor
timestamp: January 03, 2014, 05:38:44 pm
content: Rule of the thumb - 78xx series regulator do need 100nF ceramics on both input and output.What about unused inputs of L293 chip? Connect them according to datasheet so that you do not have any funny stuff.

author: unknowndomain
author_rank: Regular Contributor
timestamp: January 03, 2014, 05:54:45 pm
content: Hey Alana,Thanks for your reply, I have updated drawing above of the power circuit, I have looked at the datasheet and done some reading and see no indication of connecting the unused pins anywhere, that aside I did connect the 3,4EN pin to ground so the unused pins are high impedance, not sure what else to do?Tom

author: unknowndomain
author_rank: Regular Contributor
timestamp: January 03, 2014, 05:56:54 pm
content: Another thought, do I need 4 caps on each reg, would one 10uF on the input be okay, and drop the other ones, and keep the 100nF ones?

author: Jon86
author_rank: Frequent Contributor
timestamp: January 03, 2014, 06:04:56 pm
content: Unless you need really clean power, I wouldn't bother with ALL the caps, sometimes I just put 1uF behind and 1uF in front, works fine for simple circuits.

author: mariush
author_rank: Super Contributor
timestamp: January 03, 2014, 06:17:07 pm
content: Hmm some questions.How much current is that motor going to pull?How good the 9v power supply is going to be? Is it the unregulated kind that will show 10-12v at low loads, under 9v when lots of current is pulled? Or are you planning to use a 9v battery?Keep in mind that 9v batteries can only provide 100-200mAh reliably. If the motor uses more current, you should at least use a largeish capacitor at the input to make the battery happier (1000-2220uf/16v wouldn't hurt)1n4004 is good for 1A max. Of course it will last for more than 1A for a few seconds of motor running, if motor uses more than 1A.The reason I asked what 9v supply you have is because the 1n4004 will drop about 0.8v at 100mA and about 1v at 1A. So you'd really have 8 - 8.2v input voltage. To get this voltage drop lower you may want to use a schottky diodes like 1n5817-1n5819 which have an average of 0.3v @ 400mA , 0.6v @1A.I guess you use it as a sort of reverse voltage protection - look into using mosfet for that, you won't lose any voltage using mosfets. Afrotechmods on Youtube has a video about it.This voltage drop is important because linear regulators like 7805 and 7806 need about 2v about the output voltage to give you proper output voltage. So the 7806 may not give you 6v if the input voltage goes under 8v, which may happen with a 9v battery or a lousy 9v power supply, especially when the diode is dropping some voltage.Now for a motor, 6v or 5.8v or whatever the output will be if the input voltage goes below 8v may not matter.You may want to add a diode or two to protect the 7806 from energy coming back from the motor (inductive crap).If you want, you could skip the 7805 and just put two diodes in series after the 7806 to get about 4.75-5.1v for whatever needs 5v. Arduino and various chips you have in pictures won't have a problem with it.Just make sure the motor won't use more than 1A of current because that's how much the 7806 can handle "officially". It can probably do 1.5-2A for short periods.Regulator ICs like 1117 which officially do 0.8A have current limits set to 0.95-1.2A but I don't see in the 78xx datasheets any mention of current limits, just a peak current parameter of 2.2 amps.Later edit:If you want to power this from a 9v battery, the battery voltage will go down as it discharges. A 9v battery can still give reasonable current at as low as 7.5v but with such low voltage your 7806 and 7805 regulators won't output 6v and 5v because the input voltage will be less than 7v due to that 1n4004 diode. Even without that diode, it's still less than the 2v above output voltage.If you change the diode and your current is less than 0.8a you may want to considering using two adjustable 1117 regulators which only need about 1.2v above the output voltage to work properly (at 0.8a current, at less current they don't need that much voltage), therefore the circuit will work fine with as low as 7.2v input voltage (which may also allow you to use cheap 7.5v DC power adapters that come with routers, modems, scanners etc)

author: Hey Jude
author_rank: Newbie
timestamp: January 03, 2014, 06:18:58 pm
content: Hi there! This is Jude. Thanks very much for taking this forward - it's really exciting to see some serious brainpower on getting things like the control / user experience right! I'd wanted to do something like this myself, but had no idea how - so thanks in advance.However, may I request a few things you post as soon as you are able:1. 'inputs' - in so much as if you are using a 9V battery/adaptor changeover (like an Arduino)2. 'outputs' - if you are offering speed control / reverse / on / off / standby / lights / first-feed, etc.3. list of components / BOM. I expect you are doing this - BUT....4. also a list of hack-able components**For me this is an interesting one, as I'm considering using a HS311 Servo - and removing the potentiometer (pot to you guys!) to make the servo able to have continuous rotation. This means I have a (10k ohm) pot left over, and I think it'd be cool if this could be 'reused' in the PCB you design. It's not only good recycling, but I'm just someone who hates wasting stuff... I'm sure you'll appreciate this.Finally, are you using anything like the PCB services offered by RS or Fritzing for example? If so, do you have a layout you think it will fit on to?The reason I ask all this in advance is that since I got the 3D Printer, I'm trying to design something in CAD - and make the design open source if possible - and obviously I'd like to give your PCB design the option to be compatible, if not fully credited as the default design. Of course if you'd rather just press on with your own design and see where you get to, that's fine, but perhaps for a V2.0 it'd be cool to 'merge' our respective efforts.Best of luck and keep me posted. Thanks to everyone else who's contributed (though I understand very little, I'll try and get up to speed!).JudeHS311 -http://www.servocity.com/html/hs-311_standard.html

author: unknowndomain
author_rank: Regular Contributor
timestamp: January 03, 2014, 06:58:37 pm
content: Quote from: Hey Jude on January 03, 2014, 06:18:58 pmIt will take a standard 2.1mm centre positive power supply, but not sure if it will be 9V from the above comments, perhaps 12V.Quote from: Hey Jude on January 03, 2014, 06:18:58 pmThere is a dial for speed control, a toggle for direction, a button to feed, a power toggle, a power LED and two screw terminals for the motor, and two terminals for the remote switch on the wand.Quote from: Hey Jude on January 03, 2014, 06:18:58 pmThis will be published.Quote from: Hey Jude on January 03, 2014, 06:18:58 pmTBH it is so simple there is little hackable about it, 555 timers are the most common thing ever, and the L293 is very common also.Quote from: Hey Jude on January 03, 2014, 06:18:58 pmI am not sure why you are using a servo, I know it's in your original design but they are expensive and it requires disassembly to make it work where as the motor I have found is about £2 and has a nominal 30-40 RPM at 6V because of the gear system.Quote from: Hey Jude on January 03, 2014, 06:18:58 pmI will probably use Ragworm or OSHPark.Quote from: Hey Jude on January 03, 2014, 06:18:58 pmI am up for this.

author: Alana
author_rank: Frequent Contributor
timestamp: January 03, 2014, 07:15:53 pm
content: I just remembered that motors and voltage regulators do not like each other. I had lots of problems with electronics in a robot - we had only 12V battery and 6V servo. I tried to power servo via switchmode regulator and even with big 3x 10000uF caps on the 6V side for inrush current it would not work properly. Try to think if you could use same voltage for motor and power so that you would avoid my problems.

author: Jon86
author_rank: Frequent Contributor
timestamp: January 03, 2014, 07:18:30 pm
content: Quote from: Alana on January 03, 2014, 07:15:53 pmSwitchmode maybe, not so much with linear.

author: unknowndomain
author_rank: Regular Contributor
timestamp: January 03, 2014, 08:05:11 pm
content: Quote from: mariush on January 03, 2014, 06:17:07 pmThe motor I am planning to use isthis one from Rapid Electronicsit claims a 150mA no load current draw, presumably this will be less than 1A on light work, need to test this though.Quote from: mariush on January 03, 2014, 06:17:07 pmI am think about switching over to 12V and powering the motor direct without onboard regulation as the motor will accept this and the L293 accepts up to 36V and as I am having speed control there is no need to reduce the voltage.Quote from: mariush on January 03, 2014, 06:17:07 pmThis becomes a non-issue if I power the motor directly into VCC2 on the L29 so that helps, thanks for the notes, will consider that in future and check out the video, this is for reverse voltage protection.Quote from: mariush on January 03, 2014, 06:17:07 pmI believe there are clamp diodes in the L293.I am going to make some changes and come back with a revision.

author: unknowndomain
author_rank: Regular Contributor
timestamp: January 04, 2014, 03:13:39 am
content: Okay I have made some changes, I think it's pretty close to done, I am planning to order some parts to do breadboarding before I order.I am still a little unsure and have some questions:Will the 555 generate a PWM?Will that be suitable for driving the enable pin?Will the pull down resistors work for the direction switch?Is it okay to send the PWM signal through a switch on a 50cm wire and back again?Thanks again for the help, updated images at the top.

author: sleemanj
author_rank: Super Contributor
timestamp: January 04, 2014, 04:08:09 am
content: Quote from: unknowndomain on January 03, 2014, 08:05:11 pmI recommend external diodes anyway, even if you don't install them, that way you (or somebody) can easily substitute a pin-compatible part (eg Sn754110) which doesn't have clamp diodes (or in the case of the Sn754110 isn't well defined). A pads for surface mount diodes don't take up much space.

author: unknowndomain
author_rank: Regular Contributor
timestamp: January 04, 2014, 04:14:56 am
content: Quote from: sleemanj on January 04, 2014, 04:08:09 amHey,I will consider that, it's just an issue because of board space, but it's worth considering.Anyone able to help with my above questions?Tom

author: unknowndomain
author_rank: Regular Contributor
timestamp: January 07, 2014, 11:49:13 pm
content: Okay, I have prototyped the circuit and kind of works..I initially forgot to add the 100nF cap and it was buggy but worked... when you turn the pot it would start off at one end at near full speed, then as you turn it it suddenly goes to low speed, then as you continue it ramps back up to close to full speed.Whats annoying is that I don't have a 100nF cap so I tried a couple other values 220nF and 47nF and neither worked, the motor just doesn't run, equally when I just go straight to ground it runs full speed only.I don't really understand why this isn't working, clearly the L293 is fine, I did add a 10K pull down to the 1,2EN pin because when it was floating then it would run full speed, now the button works, but the 555 isn't outputting anything that makes sense.Please help!

author: Alana
author_rank: Frequent Contributor
timestamp: January 08, 2014, 12:22:54 am
content: If you have scope look at your PWM signal - i think something is wrong there. You may try my circuit for PWM generation - it works from 1% to 99% and i was able to control speed of PC case fan with it.I had to play around with it to put PWM frequency above audio frequencies and i ended up with R1 = 10k and C1 = 10n but for a normal motor you may have to do the opposite = get down to low frequencies. Try to experiment with this.