Re: Are there any Ex GPO engineers here? Dorman Lamps
The lamp-flasher circuit was always intriguing: an optically-coupled multivibrator.
Bulb lights, shines on photocell, photocell turns bulb off. Include the hysteresis of the photocell, the thermal-lag of the bulb and a bit of capacitance and you've got a nice simple oscillator. The truly-cunning bit [ which surely should have been patented!! ] was to let the photocell also 'see' daylight - so during the day the oscillator was locked-out so saving battery-power.
Musing on this, I recovered a dead modern version from the hedge on my morning dog-walk and disassembled it. Seems they're now made by "UNIPART/Dorman" [ yes, the "Unipart" being the same as the late-and-unlamented 1980s supplier of replacement parts to failing British Leyland cars]. These days the electronics are a couple of SMA transistors and a half-dozen resistors/capacitors/diodes which drive a yellow LED as the light-source. The power-supply is still a (single) spring-terminal 996 battery.
As part of 'idiot-proofing' cunning the place the square battery fits is engineered so that whichever orientation you install it, everything still works: there are 4 contacts for the outer battery-spring and one for the centre. This I like !
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