Atart power switch for a retropi project

DocShady

i recently dug my familys old Atari 2600 out of storage. It was dead and I was unable to repair it so I decided to turn it into a retropie project.

I'm using a Raspberry pi 3 for this but I have salvaged some parts from the Ataris mainboard. Namely the 2 of the 4 main silver switches. The on/off will be used just for that purpose, the other momentory switch will act as a reset. They are practical and keeps the astetic of the console intact. (The other switches have been replaced with USB ports)

My issue my is my lack of experience with this sort of thing. The on/off switch has 6 poles and I'm pretty sure the power setup for the pi uses 2 wires, so I;m not sure how to put this together. Anybody have any experience on wiring up an atari 6 pole switch for raspberry pi power?

ClassicGMR

@docshady I'm no electrician but I have taken apart said switch a few times in my life trying to fix 2600's. The switch is nothing more than a slider. Make sure you open it up, BE WARY OF THE SPRING IN THE RESET SWITCH if you do that one, and clean all the contacts.

So let's do a pinout and assume 1 and 2 are the top pins:

1 . 2
3 . 4
5 . 6

So let's say, to keep it in line with the original setup, you want it to be slid UP to power ON. You'd run a positive lead in to 1 and out from 3. Negative would be in to 2 and out from 4. 5 and 6 are null connections. So what that should do is break power when you slide the switch down.

Now keep in mind I have no electronics training. I don't know how much resistance or current the switch adds/carries/etc. so you may want to wait for someone more qualified to ask but it seems a fairly straightforward build if everything is set up right.

I found a "Micro USB Male Plug Cable 2 wires Power Pigtail Cord DIY" and "USB Type - C Male Plug Cable 2 wires Power Pigtail Cord DIY" on eBay. There's also female variants of each for power to be plugged in. Might be worth a look.

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Have I mentioned I'm not an electrician? Remember that. Just my $0.02 and what I would try.

Lolonois

Welcome to the fun house @DocShady ,

Vcc from PSU --->-------1-o-o 2
                        3 o-o-4------>--- Vcc to Rpi
                        5 o o 6
						
Gnd from PSU ------------------------>--- Gnd to Rpi

I would suggest wiring like above. Note that 1-2 are bridged and 3-4 are bridged too. This wiring is a safeguard if the path 1 to 3 or 4 to 6 oxides/ages: So you will still have the other path. If you look close at the pictures of the Atari repair guide [1] (Thanks @ClassicGMR ) you will see the Atari engineers did the same. There is no need to switch the Ground line.

Although not asked but a word of advice for the PSU: I guess you made some math or have experimented about how much current your setup needs (Rpi 3, but may be later Rpi 4 drop-in replacement?, Overclocking?, Compile packages from source?, current draw of USB connected devices?). From my experience cheap PSU are too expensive: You have to buy twice. ;)

Look for an PSU which can devliver 5V even under your Rpi's load and has enough juice. With 3 Amps you should be on the safe side. This guy [2] has a comparision of USB PSUs for example.

If you are uncertatin or cannot find a decent USB PSU go for a 9V or 12V PSU and put an adjustable buck-converter [3] in between the PSU and the Rpi. Adjust the buck-converter to approx. 5.1V (everything up to 5.25V is within the safety range of the Rpi). Make sure the buck converter can pass at least 3A (the ones with power MOS-FET will do). They have half the size of a match box, so should fit into your housing and do not need an additional passive heat spreader.

Edit: If you choose the buck-converter approach you don't need a 3A rated 9V PSU. With 5.1V you target to 5.1 x 3A = 15.3 VA. Assuming a >=90% efficiency of the buck converter a 9V PSU with 2A is sufficient: 9V x 2A x 0.9 = 16.2VA. At 12V, min. 1.5A rated PSU will be sufficient.

Also, I refrained from the Rpi via powering USB. Even if you can buy AWG24/28 labeled mirco USB cables you only know what you really got once you cut it apart and then the connector still must fit tight into the Rpi connector.

Instead I do fuel my Rpi via the GPIO header (2xVcc and 2xGnd, see below) with a PSU that delivers constantly 5.0 to 5.1V. So no yellow bolt, ever since. While the peripherals do run fine with below 5V, it is the SD card controller which may cause issues.

Speaking on wire gauges (AWG [4]): If you cut a two DuPont wire in half so you have four halfs. Usually they are AWG24, can handle up to 2x2.1A. You can power the Rpi with two lines for Vcc and Gnd each (double check before powering on if you picked the right pins [5]). Solder the open ends to an AWG22 better AWG20 (up to 5A) and from there to the switch / PSU.

Have fun.

PS: Once done feel free to post some images in "Project and Themes", it may be positive for your upcyling karma. :)

[1] https://vintagegamingandmore.com/atari-switch-repair/
[2] https://lygte-info.dk/info/indexUSB UK.html
[3] https://en.wikipedia.org/wiki/Buck_converter
[4] https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes
[5] https://pinout.xyz/#

DocShady

@classicgmr @Lolonois Thanks a million guys. Lots of great information here. Being a bit on the new side but not afraid to get my hands dirty and learn, I have a lot to decipher here.

Now from other information I've dug up on power switches for the pie, some guides make it much simpler but completely different then what you guys are suggesting. One guide has a simple N/O momentary switch connected to pins 5 and 6 on the GPIO. This is what is was expecting. Is it so much different because of the switch I've decided to use?

Lolonois

@docshady When using a normally open (n.o.) momentary switch "something else" has to keep the state and has to evaluate the signal from the GPIO. On a flip-switch (like yours) the switch itself keeps the state.

Eventually, it is a matter of taste / design decision of yours.

If you are uncertain: Experiment with both setups and then choose what you prefer most.