This circuit is from a 1978 publication, but it can be assembled with BC548 transistors. For the comparator, we can use the LM339 instead of the uA710, which can no longer be found easily. The sensor can be any photo diode. The circuit uses a scale with 12 V lamps. They can be replaced by LEDs with 470-ohm resistors in series. The circuit is powered by 15 V.
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