short circuit :/

May 11, 2007 4 Replies

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Jan Nielsen 19 years ago

Hi,

I made a circuit for a simple serial temperature system, it worked on the breadboard, but something has gone wrong since.

Before I apply power to the board I have 4.3V (3xAA), when I apply power the voltage drops to 2.5 and keeps dropping, I added a LED to see if it worked, and it dosent.

-So im guessing its a short circuit right ?

The "diagram" is here

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The green connections is made with jumpwire, the board is standard single side that I etched. The custom components are a jackconnector (bottom right), and just

3holes for a LM35 (VDC+, Output, GND), the 4dot is not used for components. The IC is a picaxe 08-m.

I have tested the connections from the jack (bottom right) and they look ok, however several places in the circuit where traces shouldnt be connected together I get 5MOhm+ instead of a O.L. on my meter, is this ok ? VDC+ to VDC- gives 11MOhm in disconnected state.

I checked the solder and traces and it looks ok, is there some mistake in my diagram ?

Thanks, Jan

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Rev. 11D Meow! 19 years ago

You keep that s*it up and some sort of Black Hole will become your Solder Sucker!

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Jan Nielsen 19 years ago

Rev. 11D Meow! skrev:

Thats very helpful, thanks. Oh and topposting is wrong.

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Chris 19 years ago

Hi, Jan. First off, test the batteries -- 4.3V sounds a little low, and suspicious.

If you've got a 100 ohm resistor around, try placing that across the batteries, then measuring the voltage (anything up to 220 ohms will work here, too). You should be getting a pull of 45mA (less for higher ohms), a good load for AA batteries. Your battery voltage shouldn't drop by more than a tenth of a volt. If it drops more, get some fresh batteries and try again.

I wouldn't worry too much about high meg ohm readings as far as finding a short. You did well in checking the unpowered resistance from V+ to COM. Double check to make sure you haven't tied competing outputs together, but it sounds like you've got that end covered. You might want to put a cheapie DMM on your long list of things to buy.

One of the harder parts for hobbyists is the experience. You have to buy it one "D'oh!" at a time. If it turns out to be the power source, just keep it in mind next time.

Good luck Chris

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Jan Nielsen 19 years ago

I changed to 3new and got 4.7-4.8 without load.

Found the high ohm resistance was coming from a sensor, but it is ok. I have a somewhat expensive DMM that works fine, well except for ampere, luckily thats just a fuse.

In the end it turned out to be a mixup in my drawing and mirroring for the solder side, its working now.

/Jan

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