We found this circuit in a Philips documentation from 1965. The circuit uses a common LDR sensor and the transistors are general purpose types. TR2 can be a BD135.
IDT ZSSC3230 Capacitive Sensor Signal Conditioner Available from Mouser Electronics stock, this IDT...
This circuit uses only two common transistors and provides good audio power in a speaker. Readers who...
This is the analog part of the previous circuit with the pressure sensor for the altimeter. The...