This Schmitt trigger was found in old documentation. The transistors can be of the general-purpose type like BC548 or even 2N2222.
This circuit, found in an American publication from the 1970s, produces an audible tone in a...
The frequency of the sound produced in the speaker depends on the light that falls on the...
We found this receiver circuit for modulated light in a 90s Popular Electronics. Equivalent audio...