OptoTap PCB v1

Missing R2 Resistor

The R2 resistor is missing on purpose. It's original purpose was a pullup to 5V, but this causes 2 problems:

• Almost every mainboard already has pullups for the endstop pins. As such, we would have 2 pullups in parallel, potentially creating a voltage divider between 5V on the OptoTap and whichever voltage rail your mainboards pulls the signal up to.
• Modern Raspberry RP2040-based mainboards like the Fly SB2040 and SKR Pico don't have 5V tolerant inputs like their STM32 counterparts would. So if we pullup the signal to 5V, then it would instantly damage the input pin or the MCU itself.

Because the last issue is critical and was only identified just prior release and the boards were already made, they had to be reworked individually to remove R2. You might find flux residue on the board due to that, you don't need to remove it as it is non-corrosive flux.

OptoTap LED always on

If the OptoTap LED is always on you probably have mixed the GND and SIGNAL connections. It's good practice to use a multimeter to verify that all connections are what you think they are prior to power-on.

OptoTap PCB v1 - Alternative Sensor Information

Due to part shortages, a small number of OptoTap boards needed to be populated with the OPB960L51 variant of the sensor. Functionality is exactly the same as the other sensors, but you need a different printed part for it - download it from here (left variant).

Also this sensor requires a 5V tolerant input. Any STM32-based MCU has a 5V tolerant input (fitted on EBB36, SHT36). For the FLY-SB2040, you need to use the HV endstop input (gpio25) as this one contains a diode to protect the MCU.