Hey all, I thought I’d post about an issue I found with the Grove Digital Distance Interrupter (0.5 to 5cm). I purchased two of these sensors from Digikey, and for the life of me I couldn’t get either one to trigger at all! Checked and rechecked that the board was getting a nice clean 5V power supply, tried all manner of materials to reflect the IR, tested with and without the output connected to something… nada.
Eventually, after digging through the data sheet for the IR sensor and looking at the schematic for the sensor module, I noticed a discrepancy: The 4.3ohm resistor connected to the LED_FB pin is the correct value only if the supply voltage to the sensor itself is 5V. But the sensor board is assembled such that the 3.3V regulator is active, meaning the sensor is being supplied with only 3.3V. That means the IR LED will not receive enough current to operate!
The solution? If you plan to run the sensor board from exactly 5V (say, a USB port), then move the 0ohm resistor from position R3 to R4. That will take the 3.3V regulator out of the circuit and allow the sensor to work with a full 5V supply.
If you are running from an unstable or otherwise not-quite-5V supply, you’ll want to make use of the onboard regulator. Changing the resistor R1 to 2.8ohm should do the trick.