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Basic Electronics » Simple Power Switch

May 05, 2010
by avicell
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OK, I'm almost embarassed to post this, but.... I just bought a NK and have been enjoying it for the past couple days. I decided to use the second SPDT switch as a power switch, so I wouldn't have to keep on un-plugging the battery to check the temp in my hotel room (it gets cold here sometimes!). The switch works fine, but, I put my multimeter up to it and found that there was ~2V knockdown (so, in essence, the input V to the regulator is now 7V, not 9V). Any particular reason why this is happening?

So the battery is going into Pin 1 of the SPDT, which also has a wire going directly into pin 1 of the voltage regulator. Pin 2 of the SPDT is to ground, and Pin 3 is empty. The unit is powered when the switch is pushed over above the Pin 3 side (this has always seemed backwards to me), and is powered down when the knob is over the 1st pin.

(Also, some cool things I noted with the temp sensor - a powered wire running next to it heats things up (inducted current, perhaps?); and, gently waving your hand in the direction of the temp sensor cools it down a bit. Neat!

May 05, 2010
by mongo
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Things should not be heating up... That sounds like an excessive load on the power side of things and is draining the battery on you. Double check your connections and wiring on the board. But,,, That's why using the 9V battery is recommended - to help prevent damage.

May 05, 2010
by bretm
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It sounds like you've wired it so that current flows when the switch is open and shorts the battery to ground when the switch is closed. But I can't tell for sure without a diagram and when you say "the battery is going into..." I don't know whether you mean the + or the -.

May 05, 2010
by Rick_S
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You should wire it so that the red wire from your battery goes to pin 1 and the center pin of the switch goes to the battery (V+) side of your regulator. No part of the switch would be grounded.

From your description, I believe bretm is 100% right.

Rick

May 05, 2010
by bretm
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And the reason for only seeing 7V is that you've drained the battery. You'll probably only see 7V even without the switch now.

May 05, 2010
by avicell
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I think you're right bretm, when I woke up the battery was drained. Guess I have to go buy a new battery now! I will re-wire per Rick's suggestion. Thanks for the help!

I had the + side of the battery going to pin 1 and the - side going to the ground rail.

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