valid signal on pic ports

[kutalinelucas]

hi. i'd really appriciate some help

what would be the easiest way of ramping up a 3v signal to 5v to be a valid high logic state to input to a pic controller?
i have 6 input signals which pulse high periodically at 3v (from it's own power supply) and i would like these to register on the pic pins. Im new to electronics and i've just had a quick gander at op-amps, seems pretty tricky, or are they relativly straight forward? or is it not the way to do it
thanks for looking

 

[Nigel Goodwin]

You could most probably just connect a 3V logic signal directly to the PIC pins! - have you tried it?.

 

[kutalinelucas]

no, im just trying to design the pcb now, i need to get the board printed on tuesday and either my pic programmer or chip has just started playing up so i cant really give it a go. so you think it'll be ok?

 

[Diver300]

PIC controllers that run on 5V generally have two types on input.

TTL level and Schmit Trigger inputs (TTL and ST)

You can find the type in the I/O port section of hte data sheet.

A high input on a TTL input should be at least 2 V. A high input on a Schmit Trigger should be at least 0.8 x supply, which is 4 V with a 5 V supply. So it would be best to connect the 3 V signals to TTL input ports, but as Nigel says, it might work anyhow on the Schmit Trigger inputs.

It would certainly work if you reduce the PIC supply voltage a bit.

You can see the specified figures and typical values in the "Electrical Specifications" and "DC and AC Characteristics Graphs and tables" sections of the data sheets.

 

[kutalinelucas]

brilliant, i'll just stick to a&b for the inputs then
superb.
If i could just ask one more question i should be set for a bit.

would 3 aa batteries be ok to supply 2 pics (on the same pcb be preforming different functions), an lcd display and a 3v device if i put in a voltage divider? again i would try it but i think my pic's given up

 

[kutalinelucas]

I'm sorted for now, thanks for helping