This simple Bargraph photometer with 4 LEDs was found in a 1997 documentation. The scale is adjusted in a trimpot and the sensor can be any common LDR. Power can be supplied by cells or battery.
The time constant of this circuit is 100 x R1 x C1, which leads to the possibility of obtaining times...
This circuit with a double-gate MOS transistor was found in a Popular Electronics from the 90's....
We found this circuit in the 1994 Linear Applications Handbook from National Semiconductor. The...