This ultra-simple photometer uses an LDR as a sensor, and as an indicator a common 200 watt microammeter or even a 1 mA milliammeter.
The circuit is very sensitive with power from only two small (AA) or even AAA batteries.
P1 adjusts the full scale of the instrument, ie the current with the maximum illumination of the LDR in the desired application.
In figure 1 we have the complete diagram of the photometer.
Their assembly can be done on a small terminal strip, as shown in figure 2, or in a contact array.
The LDR is of the ordinary round type and P1 must be reduced to 47k if the indicator is 1 mA.
Material list
LDR - round common LDR
M1 - microammeter or milliammeter - see text
B1 - 3 V - two AA or AAA batteries
R1 - 10 k ohms x 1/8 W - resistor - brown, black, orange
P1 - 4k - trimpot
Several:
Battery holder, terminal strip, mounting box, wires, solder, etc.
