This circuit was obtained from Linear Technology documentation from the 80's. Powered by 5 V it can be used as a shield. The components are from the era.
This circuit for a digital module was found in the September 1989 Radio Electronics magazine. The...
This 1970 Philips circuit uses a mechanical counter. The circuit is triggered by a reed switch...
We found this circuit in an old Mullard (Philips) documentation. The sensor consists of a...