G'day.
I just want to share an example of a trivial use of a PIC 16F84 (very
little code and very little hardware), but to do the same thing with pure
hardware would have been a curse.

The project is a controller for a bilge pump in a sailboat. (Yes, I know I
can buy such things, but this is more fun).

When the water level in the bilge reaches a certain level, turn pump on.
But ONLY if the water is detected continuously for 15 seconds, so that
water sloshing about 'cause I'm pounding through the waves doesn't trigger
it. Pump till water is no longer detected, but ONLY if there is no water
for 15 seconds (same reason as above). And if for some reason the pump
stays on for an hour, shut system down, since pump isn't rated for
continuous duty. Also, use a single LED to indicatce status of device:
brief flash to show power is applied, equal period slow flash to indicate
water detected, continuous to indicate pumping, and rapid flash to
indicatce shutdown due to long running.

PITA doing that with 555 timers, etc. A breeze with the PIC.

I used two stainless steel bolts as the sensing element. Local city and
sailing water (fresh) look like 20K ohms or so when the bolts are about 1
inch apart. Use a series divider with a resistor from 5V to a PIC port,
then the sensor to ground. PIC can sense water vs no water. Great.

Then read somewhere that doing this sort of thing can cause corrosion and
plating of the bolts due to using DC. One should really use AC to excite
the sensor. Makes things messy. HOWEVER, by driving the resistor/sensor
between two pins on a port, and by driving on pin HI, the other LO, then
reversing this (and equalizing the size of the loops involved), one gets AC
on the sensor, and avoids the corrosion/plating effect.

Drive a power MOSFET from the PIC to control the motor and there it is - an
automatic bilge pump controller. The same idea could be used to control the
level in a tank.

Minimum component count (PIC, resonator, 3 resistors, 1 LED, 1 MOSFET, one
diode across motor for spike protection).

Component count NOT using a PIC: scary. Plus the wiring or PC board layout.

The point of this is to show that a trivial project could be an ideal
candidate for a PIC, when you compare doing it without a PIC.

Larry (with dry bilges).



Works like a charm.
Larry Bradley
Orleans (Ottawa), Ontario, CANADA