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# Problem with connecting two LDRs

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#### zeeba

##### Junior Member level 2
LDR connection-help-

Hi

Im sensing the lights with 2 LDRs and using them as an ADC inputs to PIC 16F876A
the code should see the difference and gives an order to DC motor to move

right now my code is fine the only problem I have now that the LDRs read different readings but there is no output from the pic.

without the ldrs, when I put different voltages instead of them I get an outout from the pic

that means there is a problem in the LDR circuit right? how can I solve it?

Im connecting them same as this picture

#### keith1200rs

##### Super Moderator
Staff member
Re: LDR connection-help-

The most likely problem is the range of resistance of the LDR is outside the range that would allow your circuit to work. The simple solution may be to change the potentiometer values but first you need to measure the LDR resistance with a multimeter under the light conditions you are using.

Keith

#### zeeba

##### Junior Member level 2
Re: LDR connection-help-

The most likely problem is the range of resistance of the LDR is outside the range that would allow your circuit to work. The simple solution may be to change the potentiometer values but first you need to measure the LDR resistance with a multimeter under the light conditions you are using.

Keith

ok if I measured the LDRs then whats next what do I need to take care of?

#### keith1200rs

##### Super Moderator
Staff member
Re: LDR connection-help-

You want you potentiometer value to be at least as big as the trigger resistance of the LDR. So if you want the circuit to trigger when the LDR is 100k then you would use at least a 200k potentiometer.

Keith

#### zeeba

##### Junior Member level 2
Re: LDR connection-help-

You want you potentiometer value to be at least as big as the trigger resistance of the LDR. So if you want the circuit to trigger when the LDR is 100k then you would use at least a 200k potentiometer.

Keith

LDR1=5k ohm and LDR2=11.3Kohm and Im Connecting variable resisters both=10k

---------- Post added at 15:26 ---------- Previous post was at 15:01 ----------

the problem is that im not getting enough volt from the LDR circuit to feed A0,A1 the voltage is very small
A0=0.18V and 0.1mA
A1=0.11V and 0.1mA

what do you suggest??

#### keith1200rs

##### Super Moderator
Staff member
Re: LDR connection-help-

Those numbers don't make sense. If the LDR is around 10k then you should get around half rail on the inputs. I also don't understand the significance of the 0.1mA.

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