Here is a cost effective way to make a simple moisture detecter. You can obtain parts from any electronic supplier store or radioshack. It will be easier if you have soldering experience or you know a little bit about electronics.
-1 Light Emitting Diode(any colour)
-2N3904 transistors(2 of them)
-10 ufd electrolytic capacitors(2 of them)
-4700 ohm 1/4 watt 5% resistors(3 of them)
-330 ohm 1/4 watt 5% resistor
-printed circuit board(2.5-3 x 5-6 cm)
-9-volt battery snap
-3 copper wires(5" or more)
Parts Layout Diagram:
How to Build:
1. Clean the printed circuit board with steel wool before drawing the circuit. If the board is to big, cut it to the appropriate size or you may be able to get it precut at the store. Draw the circuit on the printed circuit board with a permanent marker(fine tip works best). Draw it exactly how it is shown. You dont need to draw the yellow dots in the center of the black dots. Those just indicate where you drill the small holes. When the ink dries, apply another coating. Make sure you draw the circuit in the center.
2. Make sure the circuit is neatly drawn and clean. Now, get a glass tray or cooking tray and poor ferric chloride solution in it. Make sure the solution is new for best results. Drill a small hole in the corner of the board and attach a wire in it. Dip the board in the solution and jiggle it around to aggitate the solution which removes the unwanted copper off the board. Do not splash the solution around too much because it will stain your clothes. You can buy the solution at a chemical store or hardware store. Do that for about 15 minutes or untill only the black lines are left on the board.
3. Clean the board with water after you take it out of the solution. Dry it and clean it again with steel wool untill all you see is clean, shinny copper in the circuit pattern. Now use a small drill bit and drill holes where the dots are in the diagram. You can make the dots alittle bigger to make it easier or you can use a tiny drill bit. When that is done, clean the board again with steel wool. Now you can rub flux on the circuit pattern and solder the circuit lines. Do not use too much solder or it will be lumpy and un even.
4. Now you can assemble the components. Feed the leads of the component that you are soldering through the appropriate holes. The diagram should help you alot. Solder every part as it is layed out on the diagram. When soldering the capacitors, make sure the negative sides(the side with the sort wire lead) of each capacitor are facing eachother. Now solder the transistors and try not to take too long on these because they can be damages by too much heat. Now solder the LED last. The negative side(the short LED) should be on the right side of the board. Caution: use a heat sink when soldering the LED because they can be damagesd by heat. If you dont have a heat sink, try to solder one side quickly, wait for it to cool down, then solder the other side. You can make a simple heat sink by soldering a small alligator clip onto an insulated wire, then covering the clip part of the clip with rubber insulator. When soldering, clip the lead that you are about to solder on the side with the component. Now solder the wires from the battery snap. Red is in the left side, and black is on the right. Now take your precut copper wires and solder them on to the three lines on the bottom. The shoud be sticking down strait. Now stick them in the soil of the pot. With the battery connected, the LED will blink. The faster it blinks, the more moisture the soil has. So you have to stick the coppers all the way into the soil for best results.
-Draw the circuit exactly as shown
-Assemble the components exactly as shown
-Do not join any lines together that are not supposed to be
If you hav any questions or you need any help, please post them and I will try to help you as best as I can. You can also get help from someone else who has experience with printed circuit boards and soldering.