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Wilf Rigter's SIMD1 V3
Part of a family of nocturnal solar engines (all circuits on this page © Wilf Rigter ; note that the majority of this explanatory text comes from either postings by, or correspondence with Wilf)

The SIMD1 V3 is very similar to the NPN flavor of SIMD1 V2, but with the addition of a FET on the output line. This makes life easier for its attached load (since there's no need here for something that can use an "enable line"), by providing power that's just "there" in the dark. Here the FET is used to sink load current from a pummer, motor, or whatever.


Turn-on is crisp, and the circuit switches rapidly when the light drops just a little. As with the other SIMD1 circuits, the 1M resistor across the solar cell can be changed to a smaller value (i.e. 100K) to adjust sensitivity and make it turn on even faster (with a corresponding loss in charge efficiency).

Parts list for basic circuit
Radio Shack

Storage capacitor


Solar cell


2N3904 Transistor

$0.15, #TR3904
$0.26, #2N3904-ND
$0.07, #900-5456


2 X 1 MOhm resistors

@ $0.20, #R1.0M
5 for $0.28, #1.0MQBK-ND
@ $0.07, #900-0291

I suspect that the FET could be replaced with a PNP transistor, but haven't tried this yet...

eGroups beam and alt-beam mailing list discussion on this design

SIMD1 V3 was introduced in alt-beam list message #13744

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Page author: Eric Seale
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