Electronic – Emulating a switch with open drain outputs

darlingtonmosfetoutputswitches

I need to replace mechanical switches with some kind of digital switch. Specifically I want to sent control inputs to various arcade games that use standard JAMMA inputs, which are basically switches to ground for each button/joystick. The inputs will come from a 3.3V microcontroller, but most games use pull-ups 5V so a buffer is required.

The obvious solution is to use open drain outputs. I'm trying to decide what type is best. The two candidates I have are the SN74LVC07 hex buffer and a ULN2003 or similar Darlington array. The SN74LVC07 is MOSFET based with open drain outputs and rated up to 5.5V, where as the ULN2003 will accept higher voltages (arcade systems do use 12V, although I doubt any use it for control inputs) and is probably a bit more robust.

Any comments on which of these would be best, or would some other option entirely be better? What about unused buttons? I can't see any issue with leaving those outputs disconnected and the datasheets don't say anything.

Thanks.

Best Answer

Since you'll be driving the switches with an MCU, the 2003's inversion won't matter, so it looks to me:

                 Vce   Vcc    IC           $/pkg   $/dev
                  V     V     mA   n/pkg   DKEY1   DKEY1
              |------|-----|-----|-------|-------|-------|      
     ULN2003     50     0    500     7     0.59    0.084
     74LVC07     6.5   6.5    50     6     0.45    0.075

like the extra penny per device for the 2003 is well worth its extra robustness and versatility.

Here are the data sheets for the ULN2003 and for the 74LVC07.

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