External pull up resistors with an Atmega8a

Using Arduino Microcontrollers
#1

Hi, I'm new to this board and Arduino/AVR stuff so please forgive me if I'm in the wrong place or don't use the correct terminology.

I am in the process of repurposing a guitar foot switch which has an embedded Atmega8a microcontroller. I've figured out the ICSP connections, installed a bootloader and am now testing it. It has a bank of 6 switches which connect ground to pins 9-14 (PD and PB). Before I test the switches I want to make sure there's no chance of causing damage so here's my question - why are there are 1k external pullup resistors on those lines? I thought that those pins had internal pullup resistors so the external ones seem redundant. I assume I can test the switches without setting the pins to use the internal resistors but I'm so new to this that I need to know what's going on with the external resistors before I proceed. Thanks for taking the time.

#2

The external resistors may be pull-up or pull-down, depending on the original design intent. In either case it will not matter very much, because the internal pull-ups provide what is known as weak pull-up (they're about 100kohm I think). 1Kohm is actually a very strong pull up or pull down, as most designers would most often install 4k7 or 10k, but this is completely dependent on the design intent as noted above. It's possible the resistors are there to attenuate an audio signal, or they may be there to set input options.

In short, I'd try to determine for sure if you are seeing pull up or pull down, calculate what you expect the circuit to do, then experiment. You won't do any harm and you'll learn stuff either way.