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Diagnosing Breadboard Voltage Drops

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Brian Gantz

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Hi everyone,

I'm having some unusual problems and appreciate any help! I am constructing a simple circuit using a breadboard with a battery pack as the power source, and 1 100 ohm resistor in order to test the board and practice some basic electronics skills. However, I'm noticing a .2 V drop when comparing the voltage across the power supply leads and across the resistor. What would be some things to troubleshoot in addressing this voltage drop? Some sources seem to suggest that this might be within the error margin for the device, but I'm hoping to diagnose the problem, since I expect that the voltage drop across the resistor and the battery pack to be the same. This is my first time constructing circuits beyond the classroom, so any real world tips anyone can offer will be greatly appreciated! :grin:
 

chuckey

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Connect the negative probe of your meter to the battery. Then measure the voltage at points along the negative feed to the resistor. It should be 0V of course. Do the same again but with the positive probe connected to the battery positive and measure the voltage drop along your connections to the positive end of the resistor, which again should be 0V. Somewhere the voltage measured should jump up to .2V, now you have located the bad connection. In general you could try wiggling the connections to see if one is bad.
Frank
 

Brian Gantz

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Thanks chuckey :) I'm still diagnosing the problem - though I've been doing some additional probing. I tried what you said initially, and did find some unexpected voltage drops, but not enough to account for it all. I measured the current in the circuit, and did a bit of calculating along with the voltage to figure out the equivalent resistance causing to the voltage drop to be about 19 ohms. I'm wondering - is that typical? I completely forgot to consider tolerances in my calculations at first - so these resistors seem to have an error margin of 20% instead of the stated 5. Is that realistic? Next I plan to apply your suggestion, take detailed measurement and try again.
 

jiripolivka

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Breadboards are made of metal springs and connections are made by wire jumpers. I would estimate a maximum resistance to less than 50 mOhms. 0.2 Ohm looks like a very bad connection. Possibly dirty wire jumper?
To be sure, wiggle connections if there seems to be a problem. If possible, simple circuits are better soldered to survive testing.
 

Brian Gantz

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Thanks everyone who answered! I'm happy to say I finally diagnosed the problem - so I figured I'd thank you all, and post the resolution for others that stumble into this. Problem turned out to be the jumper cables the breadboard was using - once I made my own, each having sturdier connectors than the jumpers, the problem resolved itself. It turned out to be, as jiripolivka mentioned above, a bad connection issue. I'm going to solder eventually :) How I made the jumpers was repurposing a 9V battery connector, since the wires were sturdier than the jumpers. I cut the wires off, and stripped off the insulator on the end where I snipped. Worked like a charm!
 

SunnySkyguy

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I recall using AWG 24 solid wire for jumpers on Veroboards and also using DIP sockets to plug THT parts in the DIP socket with short leads.

You can simulate the layout using Fritzing or make your layout, look as neat as the simulation.

http://fritzing.org/home/
 

chuckey

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I find that the single core cable our telephone company uses is ideal. Its .5mm diam and comes in twisted pairs within a white sleeve, the only problem is that it has only a limited range of colours. So keep a look out when telecomm engineers are working on road side kiosks.
Frank
 

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