This circuit is from an American 80's documentation. The integrated circuit is from the time and the sensor consists of a smoke chamber measuring its transparency change.
This circuit was found in the 1992 Radio Electronics Handbook. It is used to test VCR recording heads....
These days the unijunction transistor (UJT) is not common, but IF you have one you can mount this...
This article was written by A. Fanzeres in the 1970s. We kept the original text. With the circuit we...