MIAC Volt Meter

[mimiyum]

I tried the Digital Volt meter sample program on my MIAC. That works fine resulting it voltage readings of up to 1 decimal point.

In my attempt to get a reading of up to 2 decimal points, I edited the program and when I download this to my MIAC, I get a zero reading instead. Can you please check my program to see what I did wrong. By the way, simulation of this program works fine. I just doesn't work on the actual MIAC.

Thanks!

[Sean]

Hello,

The calculations are failing at the line:
Voltage = Value/19.6

Floating-point values can not be used in integer calculations.

The MIAC analog inputs have been designed to provide a simpler conversion between the ADC value and true voltage. The divider of 20 should provide you with an accurate conversion (<1% error).

I have run your program successfully with the line modified to:
Voltage = Value/20

[mimiyum]

Thanks Sean! That works fine.

Errr...can we work around the computations to get another digit? I want to get figures like 1.234 volts?

Is the factor really 2 or is it 1.96 or another number?

Thanks again!

[Sean]

The ideal conversion factor for ADC input value (8-bit mode) to voltage is 19.968 (79.872 for 10-bit). This part of the circuit uses resistors with a 1% tolerance, so 20 is a realistic approximation.

Using either 8- or 10-bit conversions, there is a limit of a maximum of 2 decimal places of resolution when displaying the measured voltage.

10-bit mode can be useful for detecting smaller voltage changes than 8-bit can detect (precision), but the absolute values should only be considered to be accurate to apprximately 1% or 50mV, whichever is greater (12.5mV for 10-bit).

[mimiyum]

Thanks Sean for your very clear explanation! It puts things into proper perspective for me.

[medelec35]

Errr...can we work around the computations to get another digit? I want to get figures like 1.234 volts?

I have done that for you and I have changed resolution from 8 bit to 10 bit and used 79.872 as a value in the calculations. The only purpose of doing all of these is to demonstrate how it is achieved for educational purposes. As you know Sean and Ben + Sean (in a different post) said would not improve accuracy since accuracy is determined by resistors and opamp. Hope it helps you.

DVM.jpg (37.32 KiB) Viewed 8898 times

[mimiyum]

Thanks Medelec for the demonstration. I was really using this for my educational purposes---as a way to learn more about accurate ADC reading for other applications.

Now, I will attempt to apply the concept on a 16F88 or 16F877a.

Thanks again!