9 V battery charger
Nickel-cadmium battenes should normally
be charged at 1/10 their eapacity in Ah.
The capacity of a 9 V NiCd battery is usually
110 mAh and this type of battery
should therefore be charged in about 10 h.
However, the efficiency of the charger is
only around 70%, so that the real charging
period should be of the order of 14 hours.
In the present charger, the charging
time is measured by IC1, whose oscillator
is set to a frequency of 1/6 Hz, ensuring
that outpur Q13 goes high after 14 h.