PL TOS E 1/350 Lighting Kit - Voltage Weirdness

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RossW
Posts: 204
Joined: Wed Oct 02, 2002 1:04 pm
Location: Toronto, ON

PL TOS E 1/350 Lighting Kit - Voltage Weirdness

Post by RossW » Thu Jan 31, 2013 7:21 pm

I've done some quick-and-dirty voltage measurements on the saucer board that comes with the Polar Lights TOS E 1/350 lighting kit, and I can't quite work out what's going on. Normally, if you have a 12V power supply you'd need some kind of voltage regulator (e.g. 7805) to drop the voltage for the PIC micro controller chip (which I guess here is used to flash the running light LEDs) and also for the impulse engine/sensor array LEDs (since there's only 2 visible resistors).

Looking at the photo, the 12.5v supply seems to be dropped down to just over 5v by the resistor (working in concert with the Zener diode, if indeed that's what it is) and maybe the 2 big resistors further drop the voltage down to around 3v for the LEDs.

http://i188.photobucket.com/albums/z301 ... 619046.jpg

My question is this: has anyone seen this kind of circuit before? It would seem to me that dropping 7.25v over a small wattage resistor is asking for trouble. Plus, if the wall wart is an unregulated one that every time the running lights flash you'd expect the other lights to dim and then get brighter when the running lights flash off.

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