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Challenge:
Design a circuit, which can latch and unlatch +5v latching relay from a small 3 volt lithium cell battery.
Solution:
The circuit below takes advantage of some inexpensive small super capacitors. The circuit pumps 6 volt pulses into the separate 5 volt latching and unlatching relay coils. A short 25ms pulse is all that is needed to flip the
relay states. A third super capacitor is used to supply a higher peak current than a small lithium cell might otherwise be able to supply.
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