Vref on 3.3V PIC18LF

[Boomslang]

Thanks for that, I will give it a go. I read up on op-amps for the last 2 hours, and they are actually very easy to use....don't know why I always avoided them...

Just one thing, my sensor will output 0-5V, so should I not keep a V divider to bring the max sensor output down to 2.5V, and run that 0-2.5 signal through the op-amp at unity gain? Should I buffer the 2.5V ref as well?

Please see the att jpg, does that look more or less right? Are the caps in the circuit required for the 7660 (like the caps with a 7805)?

 

[Nigel Goodwin]

Thanks for that, I will give it a go. I read up on op-amps for the last 2 hours, and they are actually very easy to use....don't know why I always avoided them...

Just one thing, my sensor will output 0-5V, so should I not keep a V divider to bring the max sensor output down to 2.5V, and run that 0-2.5 signal through the op-amp at unity gain? Should I buffer the 2.5V ref as well?

That's what the two resistors at the input of the opamp are doing, dividing the 5V down to 2.5V - they need to be both the same value, where did 430K come from?.

I don't know if you need to buffer the 2.5V or not, but I would presume not?.

Please see the att jpg, does that look more or less right? Are the caps in the circuit required for the 7660 (like the caps with a 7805)?

Yes, they are required, they are what makes the 7660 work.

 

[Boomslang]

The 220K and 430K creates a divider, so that when the imput is 5V the V after the divider will be 3.3V. I am running the PIC at 3.3V.

 

[Nigel Goodwin]

The 220K and 430K creates a divider, so that when the imput is 5V the V after the divider will be 3.3V. I am running the PIC at 3.3V.

Use the 2.5V external Vref, and divide it by 2 - why would you want to use a low quality 3.3V for Vref?.

 

[Boomslang]

Oh, ok, now I see what you meant... I will do that, thanks for the help.