building multimeter using 8051

[sai]

i am considering building a multimeter using 8051...i was wondering whether the limitations of max current and voltage ratings of 8051 would come into picture for measuring high vtgs and crts..... is there any technique to increase the range of measurement...????

 

[Arkham00]

8051 is a microcontroller without any analog input so you need an external A/D converter. Of course the 8051, the display and the A/D converter will be powered by 5Vdc. To measure DC voltages and currents, you need external precision resistors connected as voltage divider to reduce input high voltage to the value correct for the A/D converter (usually 5V or less). You need extra circuits (active precision rectifier) to measure AC voltages and currents.

Take note that usually, in multimeters, the voltage under measure is not insulated from the microcontroller circuit so if you measure 220Vac, your circuit must be well insulated to avoid electrical shocks.

 

[ronsimpson]

The C8051F351 has 8 analog inputs and can measure voltages to 24 bits. That makes a good volt/current meter.

 

[Arkham00]

Good! You are using a nice variant of the 8051 architecture that has analog inputs, high speed and a lot of built-in peripherals (by the way: the original 8051, as you can see here, has no analog inputs).

From a short form datasheet, your microcontroller may use an internal Vref of 2.50V and has a separate analog power supply. The power supply, in the specs, is tied to 3.0V so maximum input voltage should be that.

Has I told in the previous message, you need precision resistors to make a voltage divider. Because your microcontroller has programmable gain amplifier, you may try to use a fixed voltage divider calculated for maximum voltage you need to measure and use the built-in amplifier to do automatic software scaling. You still need precision rectifier to measure AC. I suggest you use also an external protection to the analog inputs.

 

[Mikebits]

There is always this part too.
https://www.electro-tech-online.com/custompdfs/2009/01/fn3082.pdf