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dracu_n_dulap

ICL7107 ammeter

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hi! i want to build an ammeter with icl7107 for my variable power supply (the one on this site) but i ran into a problem with this  schematic because one of the inputs is tied to the ground and i cannot use it at rhe same time with this voltmeter. but the schematic on this site has floating inputs and i would like to use it. so if you couuld please tell me how turn it into a ammeter.
what i know so far is that i have to add a low value resistor on wich the voltmeter will measure the voltage. that value will be in amperes. so how can i calculate the power resistor on wich  the voltage is measured. i know so far that is Ohm's law, is there a specific value for the ic that you have to konw? ???

thanks.

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If you want to solve your problem use separate supplies for each meter.Thus you can use voltmeter and ammeter at the same time. I had the same problem but there's no problem after seperating power supplies(+-5V 's). Now they are working properly with my psu.

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On 8/31/2009 at 10:30 PM, dracu_n_dulap said:

hi! i want to build an ammeter with icl7107 for my variable power supply (the one on this site) but i ran into a problem with this  schematic because one of the inputs is tied to the ground and i cannot use it at rhe same time with this voltmeter. but the schematic on this site has floating inputs and i would like to use it. so if you couuld please tell me how turn it into a ammeter.
what i know so far is that i have to add a low value resistor on wich the voltmeter will measure the voltage. that value will be in amperes. so how can i calculate the power resistor on wich  the voltage is measured. i know so far that is Ohm's law, is there a specific value for the ic that you have to konw? ???

thanks.

Hi, did u got any solution for your problem coz I'm also facing same thing. Thanks

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Use a separate +5V supply to power the voltage meter and current meter.

Connect the grounds of both meters to the (-) output of the power supply being measured.

The current meter can measure the negative voltage across the 0.47 ohms R7 of the power supply being measured, then the current meter does not produce an additional voltage drop that ruins the good voltage regulation. R7 produces a voltage of 1.41V for 3A or 0.47V for 1A. You will need to make a voltage divider to reduce the 0.47V to 0.1V for the input of the current meter. Disconnect the (-) segment of the current meter display. 

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