They're probably Ada's, to be honest.
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I've just ordered three circuit boards for the initial prototype for testing/sizing, for what it's worth. $12.14 for three with tax and shipping. I'd call that a deal.
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Shouldn't the diode in the circuit diagram pointing in the other direction?
No, it's correct the way it is. When the relay is switched off, the coil inside creates a current that is opposite the former current, so the voltage is also is reverse. To protect the semiconductors (here the transistor), this voltage is shortened by the diode.
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Saved by the diode. (yay)
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The first group of three prototype boards came in and I just soldered one up since I had the parts from earlier. I'll need some thinner tie wraps to go through those holes for cable management and I suppose I'll now need to design a plastic case. Other than that, it seems to work as expected.
Back from vacation and I've now designed/printed an enclosure. I've used a simple tight rubber band which came on a William Sonoma whisk to hold the two halves together.
- $3.99
- $1.59
- $4.69
- $0.37
- $4.04
- $0.20
- $0.03
$15.00 approximate total cost of parts if you make more than one of them.
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