Solution

Using an open drain buffer like the 74LVC1G07 did the trick. Note that this part only works for inputs with a pull-up resistor. There are other parts from the same lineup that can work with any input.

Problem

I have an ebike computer that has two inputs that accept square wave signals. The range is 0-5V. One of the inputs has no pull-up/down resistors on it. When I hook up a device producing signal, the signal is detected correctly. Both highs and lows are detected correctly. The other input has a built-in pull-up resistor. When I hook the same signal to it, only the high side is detected. Measuring the voltage of the low side, it’s a bit higher than when hooked to the other input and I’m guessing it isn’t crossing the low threshold the computer expects in order to register the low.

Am I right in thinking that the pull-up resistor is increasing the lows?

Is it possible to counteract the internal pull-up resistor by hooking a pull-down resistor to the input?

I’m a software guy with decent soldering skills and minimal knowledge in electronics so please answer like I’m not the brightest electronic bulb on the tree.

Thank you in advance!

Cross-posting my question from StackExchange.