On the next two pages I show a few of the many circuits that uses only one transistor . The circuits shown can be modified and experimented with . One must remember always to use transistors that are rated for the current intended . Most transistor equivalents can be used with very small difference , if any .

This simple adjustable unregulated power supply can be used for most application by selecting a transistor rated for the voltage and current as required .

A timer to replaced the old style piano timer . Adjust RV1 for rate .

This is a fixed voltage output regulated by a zener diode See page 30 for zener resistance (Rs)calculation.Select Q1and zener for current required .

This little circuit should be used with low voltage only . It can have many applications Fun to experiment with diodes lamps , transistors , etc..

Check the desired moisture level of your plants with this meter . Use a small 1mA meter A small case and two stiff metal wires for probes will do .