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Thread: Robotics with Dan's PIC SBC
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face BY : Dan Michaels email (remove spam text)



Andy Shaw wrote:
>Hi Dan,
>Does the LM324 go rail to rail on output? If not are you using a ref voltage
>other than the supply for the A/D input, or maybe a higher voltage for the
>LM324 so you get full 0-5v input to the A/D. A year or so ago I put together
>a "general purpose" board with analogue inputs to PIC. The one thing I wish
>that I had done differently was to provide full 0-5v for the input to the
>A/D the op amp I used didn't and I couldn't fine a pin for pin replacement
>that did. Might not be a big deal for your purposes but it was certainly a
>pain to me.


Hi Andy, thanks for the comments.

My SBC40-BOT board is a little behind schedule [!!!], haven't gotten
around to breadboarding all the different ckts yet. However, regarding
opamps, I wonder what you actually used that caused a problem.

There are std pinouts for dual- and quad-opamps that are most
commonly used, so you can normally swap chips with no problems. The
CMOS devices almost all give you rail-to-rail inputs and outputs
when you need it - although they are a little more expensive:

dual:
bjt:  LM358
jfet: TL082, LF353 [my favorite], LF412
cmos: LMC6032, LMC6132

quad:
bjt:  LM324
jfet: TL084
cmos: LMC6034

The LM358 and LM324 are the same amps internally, and work
good with single-ended supplies where you need to get 0v
[ie, lower rail] on the input. Outputs do not go to the rails.

I have one ckt that uses a PIC73 with A/D ref = 5v buss, with
A/D driven by an LMC6032 which pretty much gets the rails.

best regards,
- Dan Michaels
Oricom Technologies
http://www.oricomtech.com
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