Luberth Dijkman wrote:

> there is a bread slicing/packing machine
> a PLC has 5 outputs connected to a display on the other side off machine
> in case of an error (door open, safety switch etcetera) the PLC ouputs a binary
> value
> the display connects a message to this valeu so the operator nows whats wrong
>
> the display is more broken then that its working and repair is expensive
>
> so i thougt i use a pic 16f84 with 4bit LCD connected to portb  and connect the
> 5 outputs from plc to porta (optocouplers)
> there are 30 error messages and i think the pic16f84 can handle this
> most machinery and PLC's i have seen and also this machine use 24VDC
> so i wanted to use the 24VDC and power the pic/lcd(16x2) with it via L7805

The PIC and LCD only draw 50mA or less, even
with LCD backlight so a 7805 should work with
a small heatsink since you want reliability.
You could put a 12v 3W zener in series with the
7805, so the zener drops the input voltage to
12v and the 7805 runs nice and cool (no heatsink).
Put a 47uF cap across the zener too.

Alternatively if you want to fiddle with a couple
of transistors you can use my Black regulator
which will be quite efficient for 24v -> 5v use
and won't need the 7805 regulator. See;
http://www.romanblack.com/smps.htm
-Roman

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