I have an arcade game that has 3 buttons controlling inputs to the arcade PCB. What I am trying to do is at any point that the game is on, if I simultaneously hold down all 3 buttons for 5 seconds, it will trigger the arduino to switch an output pin from low to high, wired to eeproms on the arcade PCB to bank switch them. So I’ll be sharing the already wired terminals of the push buttons to 3 input pins plus the ground to arduino.
Where I’m getting hung up is this: looking at the game PCB it looks like the buttons are already tied to pull-up resistors, and I’m guessing when you push whichever button it grounds that button’s input, causing an action in the game (looking at the schematic).
So if I bridge the wires over to the Arduino inputs, is there any need to use pull-up resistors there as well? I’m worried if I do, it may somehow interfere with the game inputs.
If I do still have to use pull-ups at the arduino, maybe I could use diodes to restrict any voltage back through the button wires to the game?
Be they pulled up or down? I can't quite make sense of the schematic portion.
But... let us assume they are taken care of on the arcade side.
I'd just try reading them with pinMode INPUT - that can't possibly hurt, as the Arduino inputs are very high impedance, and it might just work a treat and you could go to lunch early.
Common ground, natch, and assuming both sides are the same 5 volt or whatever logic level.
They appear to be pulled UP to the resistor array I highlighted on the far left which is tied to 5V. (I know that symbol is ambiguous. I had to check others that matched in the schematic that I knew were 5V)
That’s what I was thinking. The buttons’ off states are already pulled high on the game, and since all the wires are linked, the Arduino pins shouldn’t float….. in theory. I suppose I could use alligator wires to test rig it, and run a serial monitor to see if there’s any misbehavior.
So if I bridge the wires over to the Arduino inputs, is there any need to use pull-up resistors there as well? I’m worried if I do, it may somehow interfere with the game inputs.
(if the resistors in the arcade game are pullups),
It is not necessary to use the internal pullups of the arduino;
these inputs are high impedance as alto777 says, and they will follow the voltage generated by the game electronics (but if you use the arduino's internal pullups, it will be the same, as these pullups have resistance-equivalent values probably stronger than the game's).
If I do still have to use pull-ups at the arduino, maybe I could use diodes to restrict any voltage back through the button wires to the game?
no, there is no need to use diodes, (if you uses arduino's pullups) the pullups of the game will not be disturbed by the pullups of the arduino, those of the arduino have probably stronger value (they make pass less current than those of the game).
The Arduino pull-ups are equivalent to 20K-50K or something like that by spec, so are weaker. You certainly meant larger as in higher value.
The arcade pull-ups are very strong by comparison, so your conclusion is correct.
No matter which way they were pulled in the arcade circuit, there is no need for any pulling on the Arduino side.
The concerns of the OP might come into play if, say, the arcade side did relatively weak pull down, and a weak pull up on the Arduino side could compromise the logic value of the voltage.
As I said, if they are all set on the arcade side, best to just sense them extra gently with INPUT mode.
Now if those switches were in a scanned matrix the bets would have to be different.
I think the plan will be to do some temporary wiring from the arcade buttons to the input pins of the Arduino (No pull-ups) , and output of the Arduino to logic gates on the breadboard that will drive the (to be) eeproms. Write the code, and run serial monitor to make sure there are no transient interferences.
Still in a long design phase process but will post back eventually. Thanks again!!
