ATX Power Control Board

When I built the MING Pi, I needed a way to signal to the ATX power supply that it needed to turn on. I did that by cutting an ATX connector in half and soldering the Power On wire to one of the Gnd wires.

There have been a couple of times during development where it would have been useful to remotely shut off the power to the system. So I decided to make a simple circuit to allow the Raspberry Pi to turn off its own power.

The circuit uses the PS_ON signal to control the power to the power supply. The PS_ON input is connected to GND to enable the power. There’s many examples of how that works on the web just look for “Converting an ATX power supply to a bench power supply”. You’ll even find kits if you want to make your own.

However, I wanted to power a PI and a hard disk, so I needed a USB socket to power the Pi. The hard disk could connect to one of the disk connectors of the PSU. So that’s the basic circuit top right of the circuit diagram. An ATX connector connected to a USB with an LED indicator.

The rest of the circuit has two functions. Firstly it keeps the power on once the button SW1 or a remote button via J4 is pressed. It does this using a relay and Q1. Once the relay is energised, power flows through R1 keeping the circuit on. Alternatively it’s possible to power up remotely using J3 pin 3.

To turn off the system you can either remove the power completely, a kind of No Volt Release mechanism, or you can use the J3 connector to kill the power to the relay by turning on Q2 which in turn will bring the base of Q1 low turning that off. I’ve added some protection diodes to the inputs to avoid powering the Pi via the GPIO.

I’ve been reading about gpio-poweroff which should allow me to turn the Pi off automatically using the shutdown -h command.

Additional reference

https://www.embeddedpi.com/documentation/gpio/mypi-industrial-raspberry-pi-psu-shutdown-gpio-line

https://github.com/pimoroni/clean-shutdown

PCB Fabrication

PCBWay offered to make the boards for this project for free, in return for feedback on their ordering process. I’ve previously used Oshpark and Aisler for PCBs, both who have done well so that’s my main point of comparison. I’ve also made my own boards using letraset and ferric chloride and not surprisingly professionally made boards are a thousand times better than what I can create myself. They do also provide a wide range of other manufacturing services but I’m only reviewing the PCB process.

As a KiCAD user, my first point of call for a PCB project is to set the design rules. I quizzed PCBWay and their recommendation was to just upload my project as they should be able to make anything I send them. And they do provide a comprehensive list of PCB manufacturing capabilities on their website. I also found a slightly old but perfectly workable default KiCAD project from Greg Cormier, so that was used as the basis of my project.

PCBWay use industry standard Gerber files for their uploads so the first step in getting your pcbs manufactured is exporting the Gerber files from KiCAD. If you know the dimensions and properties you can start your process on the PCBWay home page and enter the details. I found you could jump straight to the Online Gerber Viewer and upload your zip file there. If anyone knows a good way to see the dimensions of a board in KiCAD then let me know.

I spotted whilst writing this, a thank you to Mike Cousins for his Open Source contributions. When I googled his name, I found a whole bunch of PCB rendering and manipulation tools.

PCBWay also support the Open Source community via a “share and sell” option, where you can share your board on their site and get commission for sales. I’ve not done that with this board but may do in future.

The next step is to provide the rest of the details about the board, note that some of the options will make a big difference in the price you are charged but most hobby projects you should be able to get for around $5. I added a stencil to my project as there were a few SMD components to be installed. But if you are doing through hole only then that is not required.

The last option is to select the type of shipping. This will obviously vary depending on where you are located, I picked the PCBWay Express option for $10.61 and paid up front for my order.

A tracking link is provided so you can see how long it takes. My order was placed on 4th August. The notification that they were shipped was 6th Aug. They spent nearly a week in the Chinese postal system and left China on 12th Aug arriving in the UK 2 days later. Another day to get through customs and a day to get up to Scotland and the boards arrived on 17th August. So 13 days total including manufacturing and shipping. Obviously if you want to pay more you can get them quicker. At the UK end it was Royal Mail who delivered the box.

The boards came well wrapped in a kind of heat shrink bubble wrap. The stencil was sandwiched between two sheets of hardboard, which looks like they had been used for drilling. I’m happy to see materials re-used like this as these would have otherwise have gone to waste.

I’m very happy with the boards, the quality, shipping and prices are quite comparable to the options available from other suppliers.

I’ve not yet soldered up a PCB but I did do a test fitting of the components which was a success. Will likely share first on social media when I do the assembly. But in summary, I’ll likely use PCBWay again.

Thanks to PCBWay for their sponsorship who have credited me back my costs for the boards and stencil.

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