Double door bell (CB7559E)

Found in an Elektor from the 90's, this double door-bell drive circuit switches a relay by triggering different points.

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Temperature alarm (CB22122E)
This circuit sensor is an NTC with a resistance of the order of 2k. The SCR can be from the TIC...
PNP Constant Current Source (CB1242E)
The load current can be adjusted up to about 1 A. The transistor can be TIP32 or TIP42. The...
Relaxation Oscillator (CB23592E)
This oscillator with common general-purpose transistors appeared in Radio Electronics magazine in...