Custom controller board w/ControlBlock

[sstallion]

All,

I am developing a custom controller board that can be retrofitted into an Atari 2600 and had a couple of questions about connecting momentary switches to the ControlBlock.

1. For an SPST-style momentary switch, what is the expected input of the switch? VCC? GND?
2. Is any additional debounce circuitry needed? The MCP23S17 datasheet indicates that a schmitt trigger is only available on !RESET.
3. I noticed a 220R 0603 chip resistor (R2) hanging off of LED+. Presumably this means this must be reworked to support LEDs with a greater forward voltage drop (ie. blue) that require less resistance.

4. I don't see any regulation on the board, so I'm assuming that practically speaking current is limited by Q1. Does anyone know offhand what this value is? I'm wanting to drive a couple of cooling fans and want to make sure there is enough headroom.

As an aside, are there any schematics available? I'm making some educated guesses with the help of a DMM but it would be good to know for sure before I go much further.

TIA!

[ortsac]

@sstallion To answer your question, this much I know:

1. One end of the SPST momentary switch (RESET SWITCH) is connected to GND.
   If you are referring to the POWER switch, it cannot be a momentary SPST but a latching type. One side of the POWER switch is connected to GND via the ControlBlock switch terminals.
2. Debounce circuitry not needed for the switches.
3. LED is driven by microcontroller (ATMEL TINY85) output thru series resistor R2. So if you need to attach an LED with higher requirements you will need to modify the circuit.
4. Yes, current supplied to RPi is controlled by Q1. Do not know its spec since there is no publish technical info on the ControlBlock.

I have posted request on this forum for schematic and technical specs as well, but have not been replied to by @petrockblog, who I believe is the designer.

[sstallion]

Perfect. Thanks!