lwmar
Member
Dear all,
I want to connect a LDR to one of the digital inputs of my chinese clone FX2N PLC (it has no analog inputs) and make that input active when the LDR is not receiving my laser's light. For that, first I measured the resistance value of the LDR and I've got this:
32kOhms when the laser is illuminating it
430 Ohms when the laser is not illuminating it
I know that the simplest circuit I can make is like this one (where R2 is my LDR), however I am asking here because I don't want to blow up the transistor and I think that over 4 Volts in R2 is probably too much. (I tried increasing R3 but in that case the LED does not light up) My intention is to connect the transistor's emitter to the PLC's input I want to drive and the collector to the common connection of the PLC (which is located next to the inputs). R1 and the LED you can see in the simulation are there just to simulate the ones located inside the PLC. I would like to know why the current meters at the transistor's base are showing 0.00 each.
Many thanks, best regards
Marcelo
I want to connect a LDR to one of the digital inputs of my chinese clone FX2N PLC (it has no analog inputs) and make that input active when the LDR is not receiving my laser's light. For that, first I measured the resistance value of the LDR and I've got this:
32kOhms when the laser is illuminating it
430 Ohms when the laser is not illuminating it
I know that the simplest circuit I can make is like this one (where R2 is my LDR), however I am asking here because I don't want to blow up the transistor and I think that over 4 Volts in R2 is probably too much. (I tried increasing R3 but in that case the LED does not light up) My intention is to connect the transistor's emitter to the PLC's input I want to drive and the collector to the common connection of the PLC (which is located next to the inputs). R1 and the LED you can see in the simulation are there just to simulate the ones located inside the PLC. I would like to know why the current meters at the transistor's base are showing 0.00 each.
Many thanks, best regards
Marcelo