Just made one of these for local Guides (Girl Scouts) project. No
PIC though :-(

Just one NPN transistor as a switch, a biasing resistor, LED, 3v
batteries and two paper clip probes. No soldering - all screws into a
4 hole pice of terminal block. If I remember right a 6K8 resistor was
about right to turn LED on if probe resistance was greater than 15K
which seemed to be a reaonable wet/dry point for my house plants.

[Completely OT] - I am looking for ideas for projects to make with
youngsters. Rules are - must screw into terminal block (ie
resistors, caps, diodes,etc and 3 legged devices such as
transistors are OK, larger SIP and DIP devices are not, buzzers,
speakers, batteries, mikes etc OK - I know I'll have to solder leads
for them). Must be fairly simple (say 4 transistor or equivalent
maximum) and must be fairly easy to explain. Since this is so [OT]
replies directly to my reader please. Any ideas may possibly get
included in a booklet for Scouts and Guides.

Brian

















Replace the probes with a reed switch and the LED with a buzzer,
put a magnet to hold reed switch on and hey -prestoi a burglar
alarm.

Brian E Jones
Centre for Java Technology
IBM HURSLEY