Аutomatic switch of range with PIC 16F877

[bojidarmlv]

Hi, guys.

I'm using PICF877 to make digital voltmeter. I'm using microcontroller's ADC and four switches to change voltage range ( 200mV, 2V, 20V and 200V ) of input voltage. The thing is that I want to make automatic range switch( without the buttons ). Any ideas how can I accomplish this ?

I post the scheme ( I'm using optional voltage source to simulate it in proteus instead of Vin ).

Thanks in advance.

[evsource]

Just a stab in the dark, this is probably not how commercial units do it, but might be one idea.

Set up another ADC channel with a voltage divider designed for the highest allowable voltage you might encounter. The PIC reads this voltage - a low precision reading, and uses it to switch some relays that switch in correct resistors automatically.