ammeter/voltmeter/ciruits

[caleb]

HI im wondering If any one knows where I can find circuits for these two devices.
I am doing a project now to make a combo ammeter/ voltmeter/ time till battery goes flat meter. I want to display all this Info on to a 7 segment or LCD display. I also would like to have a mode button so that all three devices (ammeter/ voltmeter/ time till battery goes flat meter) can share the same screen. Its kind of like a multi meter but with the added time till battery goes flat meter. I want this to run of the 12v dc battery that it is testing If that is at all possible. Any help would be greatly appreciated.

Im at 6th form level at school am I out of my depth with the complexity of this circuitry.

[Matthew]

The easiest option is to use a microcontroller with A/D converter. The majority of A/D converters will measure between 0-5v, so you will need a voltage divider to measure up to 12v. Current can be obtained by measuring the voltage across a low value resistor. If we look at V = IR we can see that voltage across the resistor is dependant upon the current passing through it, assuming the value of the resistor remains constant. You will likely need a high wattage resistor to handle the current through your entire circuit.

If you still don't understand how to construct the circuit, you should probably consider a different project.

Matthew