I have recently found a number of cheap Keyes KY-XXX clone boards (The word "HOYA" appears on the board but NOT the word "Keyes"), specifically KY-013 and KY-018, where the 10K resistor is in the wrong place. It is not soldered in the wrong place, according to the PCB, but the actual PCB is printed wrong. The resistor is soldered between VCC and GND rather than VCC and S (signal). So power-in goes straight to ground through the resistor and completely bypasses the sensor (either photoresistor or thermistor). To prove this I simply mounted the board the wrong way around so that S is GND and GND is S. Now the VCC goes to S and the sensor via the resistor forming a voltage divider and everything work as it should.
If you are happy with this compromise, and can remember 3 months later when you go back to use the sensor again, then you don't need to do anything. If, like me, it causes too much confusion and wasted time thinking you have got your circuit wrong somewhere then you have two choices. You can either:
- Paint over the labels and relabel them or
- If you have a steady hand un-solder the resistor move it 2mm to the left and solder back again between S and VCC. You will need a strong magnifying glass and needle point tweezers but at least your board will work and everything will be labelled correctly. See attached image with KY-013 on the left before repair and KY-018 on the right after repair.
