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.
We found this circuit in an American 80's documentation. The resistors must be of high precision...
The circuit shown is a Pierce type oscillator and operates at the fundamental frequency of the...
In the circuit shown in the figure we have the way to excite a small speaker from a TTL output. The...