Cds Cell Siwtch

[prprog]

I am testing the following circuit. It works as expected with one Cds cell. The behaviour is - when the Cds cell is cover it will activate the 4066 control line and the switch. When I add a second Cds to another 4066 control pin the issue is that I cannot set the Pot on a value that works well for 2 Cds cells. I suspect that Cds are not equal in resistance value, therefore the Potentiometer do not match the value for two Cds cells.

I try using resistor in series and in parallel to make the Cd's equal in resitance without success.

Please advice on alternative to calibrate the circuit with only one Potentiometer. The final circuit will used 9 Cds cells and 3 - 4066's.

Thanks

 

[alec_t]

When I add a second Cds to another 4066 control pin the issue is that I cannot set the Pot on a value that works well for 2 Cds cells.

With that circuit if one CdS cell goes low resistance it will pull down the voltage supply to the other cell. The cells interact. If you want them to be independent they should each have their own resistor connecting to the +ve rail/supply.
If you want the switches to operate at respective different voltages then the resistors would need to have different values. If you don't, then you can just parallel the control inputs of the gates and use a single cell for control.

 

[prprog]

Thanks alec_t.
I need it to work with a number of CdS cell (photoresistors) independently...but don't want to used a separate pot for each Cds cell. I will be using 9 Cds cell. Can you suggest a change in the circuit to make it work this way?

Thanks,
PRPROG

 

[alec_t]

If you want the setting for each CdS cell to be independent and adjustable then you will have to use 9 pots/trimmers . A single pot would create dependence.

 

[prprog]

Thanks alec_t. Appreciate your clear explanation. I will move on with another idea.

Thanks again,
PRPROG