Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 292

Circuit 123 and 124: Each half-wave charges C1 or C2 depending on its sign. With the next charge, the voltage
of C1 plus the rectified half-wave is fed to C2. It is thus charging up to twice (or accordingly, four times) the
voltage.
294
Fig. 3.123: Circuit 123: Voltage doubler with moving-coil instrument
Fig. 3.122: Cir-
cuit 122: Sensor
toggle switch
with moving-coil
instrument