Step 19: If Your Batteries are More Than 9v
Don't hook up the screen just yet - we need to build a small regulator for the screen.
It's very simple, just follow the diagram below.
You can use a 7805 to get 8v, or you can use a 7808. A 7808 is just like a 7805, but it gives out 8v instead. Using a 7805 is much more convenient in my opinion, because you can easily find them in old electronics. If you want to know how this works, then check the last paragraph.
The PS1 screen can handle from 6.89v to 8.5v. Preferably, it should get 7.5v, but as long as you have a decent 7805, you'll get the voltage you need. As always, test the output voltage before hooking it up!
BUILDING THE REGULATOR
To build the regulator, just solder the 220ohm resistor to the ground (middle) pin of the regulator. That will be your ground, which you must connect to the screen's ground, too.
Solder the 470ohm resistor to the ground pin of the regulator BEFORE the other resistor. Solder the other end to the output pin, and that is your 8v out, which you will connect to the blue wire of the screen in the next step.
Just like the NES's regulator, it's a good idea to put a small heatsink on this one, too.
Solder the negative lead of your batteries to the ground spot on the regulator. In a couple steps, you will solder the 8v out connection to your screen. For now, just leave the V+ input and 8v out wires disconnected.
HOW IT WORKS
This works because it is essentially a LM317T regulator, but with a higher output voltage. The LM317T is an adjustable voltage regulator. It can output anything from 1.5 to 12v with a 15v input source. All you need is two resistors. You hook them up in the same way as below, except you would choose different resistor values for different voltages. So why does the 7805 work for this purpose? Because the LM317T is simply a fixed 1.25v regulator. Experimenters rarely use anything below 5v, so a 7805 can do the job as well.