MOISTURE INDICATOR

INSTRUCTION SHEET

 

 

 

Price - Stock No 110

Price - Stock No 111 with Push Button Switch

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Schematic Diagram

PCB Layout

  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!

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