This 2mA source was found in a 1968’s Philips documentation. The transistor may be the BC549.
IDT ZSSC3230 Capacitive Sensor Signal Conditioner Available from Mouser Electronics stock, this IDT...
We found this transmitter circuit for different frequency ranges in a 1992 documentation. The...
This crystal configuration can be made with triggers of any logic. The frequency is given by the...