Hi guys,
I am looking to build a multi-meter using 8051( assembly language coding), I know that I can use an AD converter to display the voltage but what can I do to measure the resistance and the current?

Can anyone refer a link or suggest the easiest way to do this?

So far, I have figured that I can put the AD on the bus but would I need a HEX to decimal decoder on the bus to display the voltage? or shouldn't it be a binary to decimal decoder?

Thanks!

 

For measuring DC voltage, just use a voltage divider and your ADC.

For measuring DC current, pass the current through a known resistor (the shunt) and measure the voltage across it.

For resistance, pass a fixed current through the unknown resistor and measure the voltage across it.

AC voltages and currents are a bit harder to do; you will need to add a precision rectifier after your voltage divider.

Don't forget to add some clamps so that you won't try to feed too much voltage into your ADC.

As for the display, I'd have the micro drive the display directly and do the binary-7 segment conversion in software - it's just a 10-byte lookup table indexed by the number you are trying to convert.
/mike