[SOLVED] A pull-up resistor increases the low side of a signal, how can I counteract it?
[SOLVED] A pull-up resistor increases the low side of a signal, how can I counteract it?
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
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!
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Potentially silly question, but many function generators have a serial output impedance (resistance) of 50ohms which will make a potential divider with any input pull-up. A buffer would eliminate this problem as your controller would only see the really low output impedance of the buffer.