Moisture sensor

1. Check the continuity of the tracks with an ohm-meter or an electronic circuit tester
2. Turn the PCBoard over so that you are looking at the PLAIN side. From the drawing, find the locations of the components. You will need to turn the PCB around so that it coincides with the placement sheet. Remember that you are seeing the copper track through the PCB.
3. Identify the values of the two resistors by their colour bands and/or an ohm-meter. Bend the legs of the resistors to a shape that will fit into its two location holes. Push them through and firm the resistor down against the PCB.
4. Offer the transistor into its position with the flat on the body the way round that the drawing indicates. Bend the legs to fit into the holes. Push it in, but allow it to stand high off the board.
5. Spread the legs of the LED carefully so they spring into its correct holes. Push the legs just through the PCB so the LED stands high off the board. You should check that the small flat on the flange at the base of the globe is the same way round as the drawing shows. The LED is polarised - a semiconductor - and will not work if placed the wrong way round.
6. These components may be soldered in place. Refer Soldering Technique
7. Push the molex pins into the correct holes and solder. Solder the battery snap to these - RED to POSITIVE.
8. Bare the ends of the hook-up wire. One end of the wires goes to the PCB at the positions marked "PROBES". The other ends of the wires have the teardrop terminals soldered to attach to the probes.
9. If you are fitting a switch, simply cut the track of the PCBoard at the place indicated on the layout sheet. A hacksaw blade held in the hand will make that easy, but make sure that the track is severed - no leakage across. The wire in your Kit is used to join the switch into the circuit. Instead of cutting the track you can cut the red wire of the battery snap and solder the switch into the positive line. With the switch in the circuit the Moisture Indicator can be left in the pot-plant. To test moisture level just push the switch and the brightness of the LED will indicate wetness of the soil.
10. Connect a 9 volt battery and test. When you bring the two probe wires together the LEd will glow brightly. Wet your finger and move the probe wires apart on the wet area. The LED will dim off, and its brightness will reflect the wetness (or dryness) of your finger.If it doesn't work check that you have all the locations correct and that you have the LED and the diode in the correct polarity, and that the flat on the transistor is as the drawing shows.

N.B. Do not test the LED on 9v without a correct resistor. You will
blow it immediately. Either use 3 volts or use an ELECTRONIC CIRCUIT

TESTER (Kit available).

TECHNOLOGY NOTES

1. The LED is a Diode which is a semiconductor. This means that it will pass current in one direction only. It has a Positive Leg (+) (A for Anode) and a Negative Leg (-) (K for Kathode). Check the letters A & K on the drawing. This applies to the power diode IN4002 as well.
2. The transistor BC548 has three legs C (collector) B (base) E (emitter). The middle one is the Base leg. This is an NPN transistor; the E leg connects to the Negative battery pole. In this circuit it acts as a variable switch. The more leakage between the two probes viz. the wetter the soil, the more it switches on, and the LED glows brighter. If it doesn't light up in your potplant, then get the watering can fast!