Are pull-up resistors needed for a USB joystick controller?

Question

I recently purchased a USB encoder for arcade joysticks (https://www.amazon.com/gp/product/B00UUROWWK) to use with my Raspberry Pi 3 Model B.

The encoder is correctly recognized as a joystick in Raspbian, and by shorting button pins I can see the status change. Then it occurred to me that this might be a bad idea.

Since this will be used in a portable game system, I intend to use tactile button switches with the encoder (https://www.adafruit.com/product/367) instead of actual arcade buttons. My question is, do I need to use pull-up resistors with these switches? I think if I were to use the GPIO pins on the Pi, there are internal pull-up resistors that can be used. But as this is a separate, USB-based board, I wasn't sure.

I'm hoping there are enough GPIO pins to make using this board unnecessary anyway, but just in case...

DAB · Accepted Answer

Hi Andy,

It all depends upon if your joystick is just a passive or active component.

If they are passive, then the switch to ground or voltage should not impact it.

On the other hand, if the output is from an active component like an integrated circuit or transistor, then you really should use pull up or pull down resistors.

Either way, putting a 10K ohm resistor between the output and ground will ensure a safe transition and keep static electricity from getting into the electronics.

That might be useful for a USB device.

So I would go with caution until you get a full circuit diagram.

DAB

johnbeetem · Answer

The encoder image shows a bunch of what look like 10K Ohm resistors, which are probably pull-ups. Take a look at the back side of the circuit board with a multimeter and see where they go. The usual scheme is that each 2-pin header has one side grounded and the other side connected to the USB chip, with an additional pull-up to +3.3V or +5V. As you have discovered, micro-switches are usually just metal contacts with no resistors or other components.

andywest · Answer

After a bit of research I'm going to answer my own question. It looks like arcade push buttons use micro switches. There are no resistors or anything special inside, and when closed the resistance should be close to zero. My conclusion is that the small tactile button switches can be wired directly to the encoder without any resistors. Feel free to correct me if this is wrong, and I apologize for the noise. This is all new to me.