4 digit Auto-ranging Voltmeter

[vortexmc]

Hi everyone, this is a new project that i have undertaken, and i was hoping too get some advice on how to accomplish this.The project requires the construction of an auto-ranging volt meter that can measure positive DC voltages in the ranges 0v-1v, 0v-100mv and 0v-10mv. The display should 4 digits up to a maximum value of 1.000 volts. There should be an indication of some form when the input voltage is out of range. The one restriction is to use a PIC processor of 20 pins or less.

 

[Nigel Goodwin]

Sounds a nice easy project, there are a number of 18 pin PIC's with analogue inputs, use a precision voltage reference, and an opamp to condition the input levels. You will need some method of switching the input attenuation (or gain of the opamp) for the range switching.

Apart from the range switching, everything you need is in my tutorials.

 

[vortexmc]

Thank you for your reply, could you give me abit more details on how i should tackle the project

 

[slapdash41]

I already found couple of PIC based Voltmeter somewhere on the net.. so my advice is "use google" .. sure you'll find something useful..

 

[vortexmc]

Yeah i have looked, just asking for advice for some of the more detailed parts :

1.Auto-ranging

2.Effective voltage scaling

3.Software tips

anything is welcome, and i thank all for their input

 

[ericgibbs]

Yeah i have looked, just asking for advice for some of the more detailed parts :

1.Auto-ranging

2.Effective voltage scaling

3.Software tips

anything is welcome, and i thank all for their input

hi,
Use a OPA with switchable attenuator resistors.
Connect the output of the OPA to a PIC adc input.
Scale the OPA to give say +5V at the input of the adc.
Let the adc measure the input voltage and the program then decide which attenuation resistors to select on the OPA for the best resolution.

Does this help.?

EDIT: say the OPA was scaled to give 5V to the adc for a 1V signal input to the OPA.
The PIC's adc would read 1023 [max count value] adjust theOPA to give 1000 counts == 1.000V or 0.999V.

 

[vortexmc]

Yes, that does help How would i go about programming the PIC to aid in the auto-ranging, and what would be the best way to display the voltage on the 7 segment LED's, i.e 10s ,100s etc. I know it its a silly question, but i rather it be said, so that the best solution can be gotten thanks

 

[ericgibbs]

Yes, that does help How would i go about programming the PIC to aid in the auto-ranging, and what would be the best way to display the voltage on the 7 segment LED's, i.e 10s ,100s etc. I know it its a silly question, but i rather it be said, so that the best solution can be gotten thanks

hi,
Program, that will depend on which programming language you can write
Also the prommer you have available.

The 18F1320 is a versatile PIC, if not that one choose a 16Fxxx with inbuilt osc and ADC.

The 3 LED's [999] would display the three ranges you have chosen 000 thru 999.
The LED's 7 segments would be driven from the PIC ports, as would the digit select lines.
You must decide if you want Common Anode CA or Common Cathode CC, LED's.

Anything else.?