NiCad battery monitor

NiCad battery monitor elektor december 1981 — 12-21 It would seem that batteries are specifi- cally designed to go flat at the most in- oportune moment, during an interesting radio programme or when the calculator is absolutely necessary. In either case, the answer is not simply to replace pen light batteries by NiCad cells, as these need recharging too every now and then. The trouble is, very few devices are equipped with some sort of monitor system, so it is very difficult to know when the cells need boosting. To sit back and wait until they run out won"t exactly guarantee the cells a long lifespan — which, remember, was the reason why they were bought in the first place! The author felt it was high time an end was put to this situation and designed a straightforward circuit to monitor the battery voltage. The circuit operates as follows: when the voltage drops below a monitor certain pre-determined value, the current supply to the circuit is cut off to prevent the cells fro...