30/06/2015: New version released, x20 PCBs printed and coming in the mail. New source files and details on GitHub – available for sale in a couple of weeks.
13/11/14: Eagle files have been uploaded, you can find the link at the bottom. Thank you for your interest!
Many people over the internet have already found out the usefulness of having an ATX PSU, often salvaged from old computers, on their bench. It can be quite easily converted into a lab bench power supply (owners of a real one, please don’t kill me).
There are lots of videos on how to add binding posts to your PSU and how not to, but I didn’t like any of these solutions. I tried the first one, but my power supply was so small and tightly packed that wires and binding posts wouldn’t fit right in it.
Yet, I felt like it lacked some features I needed. I wanted some USB ports to power my rPi and charge my Nexus 5, and an adjustable voltage output. Furthermore, my PSU had a 24-pin ATX connector.
While I still consider myself a beginner in the enormous world of electronics, I decided to look up some guides on how to design a PCB (this time I’ve gotta thank you, Sparkfun! Both yours and Adafruit’s libraries and tutorials rock!) and have a try at it.
Fast forward some days later, my very own ATX breakout board was born.
Yes, it’s heavily based on the Dangerous Prototypes’ one, and I must thank them for this. I wouldn’t have been able to make one without them making theirs 🙂
The original board was 15 x 5cm and in my opinion had a much better design (the pot and 1 USB were on the front), but I resized it to 10x10cm in order to halve PCB manufacturing costs.
As I said a few lines up, it’s my first PCB so comments and feedback are welcome, if not encouraged.
These are the features I packed into it:
- It has a 24-pin ATX connector.
- Voltage lines are all broken out individually on binding posts.
- LM317-based voltage regulator. Using a 300 ohm resistor and a 2K ohm potentiometer, voltage range is 1.25-9V.
- 2 USB ports based on the TPS2513 from Texas Instruments. They can automatically detect what device is connected and adjust resistance on D+ and D- lines as needed. This means full compatibility and maximum charging speed on both Apple and Android devices. One of them is connected to 5v_STDBY, so that it works even when the PSU is off.
- Pretty much everything can be fused. I left -12V out because it can only carry low amounts of current on most PSUs (mine is 500mA maximum).
- Breadboard pin headers so that voltage lines can be connected to a breadboard using jumper cables.
- Voltmeter headers in order to know the LM317 output voltage.
- There is room for a 9W power resistor is your PSU needs it to stabilize output voltages. You can connect it either to the 5v rail or to the 12v one by jumpering the corresponding pads.
- Status LEDs on fused lines and USBs so you can check if everything works fine.
- Screw holes for standoffs.
- Breaking Bad art because yeah, this is science, bitch.
And this is the list of components you’d need to build it. All SMD parts are 0805 or bigger, because 0603s are so small they get lost on my messy desk.
- C1, C3: 0.1uF 0805 SMD capacitors.
- C2: 1uF 0805 SMD capacitor.
- F1, F2, F3, F4, F5: 1812 SMD PTC resettable fuses. (Littelfuse ones should work just fine, I used Bourns instead which are a bit larger).
- J1: 24-pin ATX connector. I bought mine from Sparkfun but RS also sells them.
- JP1: 3-pin header (for voltmeter output)
- JP2: 6-pin header (for breadboard output, fused)
- LED1, LED2, LED3, LED4, LED5, LED6: 0805 SMDs, choose the color you want but make sure to use appropriate resistors. You may not want full brightness and sure you don’t want magic smoke.
- R1, R2, R11, R12, R15: 3.3K ohm, 0805.
- R3: 330 ohm, 0805 (value may change – double check LM317 voltages).
- R16: 10k ohm, 0805.
- R6: 9/10W power resistor, not needed in my case.
- R14: 1.2k ohm, 0805.
- T1, T2, T3, T4, T5, T6: binding posts with 4mm hole. You may want some red ones for the positive lines and a black one for GND.
- U1: LM-317, through hole. There should be enough space for a heatsink.
- U2: TPS2513 from Texas Instruments. If you don’t have them, look up the datasheet and solder appropriate resistors on D+ and D- pins of the USB ports.
- X1, X2: USB female connectors, through hole.
Resistor numbers are off, I know.
I tried to stick to PCB design rules and to minimize the number of vias but I’m not sure I like the way I traced traces (:D). I made them as thick as possible, without diving into maths or trace width calculators, but they should be enough for most applications.
After the boards arrived, I noticed a small issue: a connection from R3 to C2 was missing. The fix was quick and easy and I soldered a little piece of a component between the two pads of all my PCBs (excluding my test one, pictured from now on).
This is how the board looks with all components soldered on:
And here it is up and running, charging my Nexus 5 at full speed. It also charges my iPad just fine.
Standoffs have yet to come in and I’m still figuring out whether I need the power resistor or not. There is also a voltmeter attached to the board, very handy.
I’m looking for some feedback from more experienced users so I can improve this board, maybe by making another revision (the next one will undoubtedly have a switching regulator!), and learn a bit more about PCB design. I am pretty happy with my first try though.
I made 10 pieces of this PCB, which was the MOQ. I’m keeping 2 of them but I need to get rid of the other 8. If you want one, just leave a message down here and you can get one for 5€ (PCB only), which is just a bit more than the cost for shipping worldwide.
EDIT: The response from the community has been great! There are no more PCBs left. I’m planning on making another revision and Eagle files / Schematics are coming by the end of the week.
UPDATE: Eagle files available here. The missing connection has been fixed and traces widened. Breaking Bad references removed. Parts numbering is more correct now, yet I still need to update the main post. GitHub repo here.