hi
i want to make a line follower with pic16f84...
i use photodiodes for detecting the line... but i d'ont understand how can i capture with the pic the voltage that came out from the photodiodes... can you explain it to me?

tnx

 

You may have to uas an Analog to Digital converter converter as the F84 doesnt have one , but other inexpensive models do have an A/D converter..

 

As williB has already mentioned, the 84 isn't a good choice, it's also obselete, and you should use a modern PIC instead. The 16F819 and 16F88 are pin compatible, and have internal analogue to digital converters.

However, for line following you can easily do without analogue inputs, use comparators to generate a switching signal from the photodiodes, you can make the other input of the comparator adjustable so you get a reliable switching signal from the line detection.

If you use the 16F628 (the 84's direct replacement), it already has internal comparators, and an analogue output for use with the comparators.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

can you tell me some comparators that work for line follower?

 

Any comparator, or even any opamp (back to the 741) would work fine.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

i bought today a LM2901 comparator... and it works.... but the output voltage is not the V+, it is <1V
why?

Attached Images

scheme.jpg (12.9 KB, 1036 views)

 

That circuit seems lacking in many of the essential components, I wouldn't expect it to work at all!.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

comparators typically have open-drain outputs. that is, for a low output, they pull it to ground normally, but for a high output, they act as an open-circuit. you need to use a pull-up resistor with it most likely.

 

so i have to put a 4k7 resistor from 5v to output?

 

Eh UnD3aD,
It looks like you haven't had much to do with opamps or the like here is a link to some tutorials, I find them very informative and I always refer back to them when I don't know where to go next in my designs
http://www.uoguelph.ca/~antoon/index.htm

Cheers Bryan1

 

http://cache.national.com/ds/LM/LM139.pdf
check out the Typical applications pages 7 - 15..

 

it's working.. not for that scheme .... ty guys.....