Flashing Driver Station Digital Input

[MacGyver1718]

We've wired some on/off switches to our driver's station, wiring the signal and ground to the switch.

Instead of getting on/off, we are seeing off and flashing inputs instead of on.

Any ideas why this is happening?

Thanks,
Team 1718

[EricVanWyk]

The Driver Station lacks pull up resistors on its digital inputs. If you do not actively terminate the pin, it will essentially behave like a random bit generator. Either add a pull up resistor or have your switch actively toggle between power and ground.

[MacGyver1718]

I am not sure what you mean by "toggle between power and ground." Can you please explain?

Also, what value resistor would we need to use?

Thank you for your quick response.

[EricVanWyk]

Your current set up either connects the pin to ground or it doesn't. I meant to set it up so it connects to ground or power.

Not all switches can do this. As a quick check, if it has 3 pins it probably can. The technical term is "double pole", meaning that it has two inputs it can toggle between.

As for the pullup method:
I like 10kOhms, but there is nothing magic about this number. You want it to be high enough that you are not drawing too much power through it, but low enough so that it does its job.
Take what ever you have laying around, make sure it is between 1k and 100k and give it a shot. You could probably get away with higher or lower, but I wouldn't bother with it.

EDIT: For reference, the digital side car uses 10kOhms on all of its GPIO pins and 3.17k on its I2C pins. We needed a stronger (lower resistance) pull up on the I2C so it could pull hard enough to hit the maximum data rate. Since you are probably working at human data rate (SLOW), you can get away with a lot of slop.