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The
circuit below uses a pair of long lasting lithium coil cell batteries to power a
latching relay circuit. With each activation of the small pushbutton, the relay
is either latched closed or unlatched open. Since coin cells can’t provide the
necessary peak current, a 500uF capacitor is used to store the needed energy.
The circuit standby current is kept very low by using a stack of five 100uF ceramic
capacitors instead of the usual electrolytic cap. An aluminum capacitor, even a
tantalum
capacitor leaks
too much current, shortening the battery life. By using the ceramic caps, the
overall standby current is only a few microamps.
The circuit uses two Schmitt
trigger inverters from Toshiba. The two inverters are configured in an
alternating latching circuit. With each activation of the pushbutton switch,
the circuit either latches or unlatches the dual coil latching relay from Panasonic.
The relay is quite efficient, only requiring a 25ms pulse to either latch the 10 amp
contacts open or close. The batteries should last at least 5 years.
Ceramic 1206 100uF Capacitor
5v Coil, 10 Amp Contacts, Latching Relay
Click
on Drawing Below to view PDF version of Schematic
