When the transistor shuts off, the current in the coil does not easily want to stop, so it “slams” against the transistor, causing a voltage spike. What is D2 for on the transmitter? Because the transmitter coil makes an inductor, this resists a rapid change in current. I found the higher the frequency, the better the receiver could pick it up. Capacitor C2 is 0.0068 uF, which with the resistors shown, gives a frequency of about 10 kHz. The 555 chip is configured as a square wave oscillator (well, almost square.) The output from the 555 drives a transistor that switches on and off, which quickly starts and stops current flow in the transmitter coil. 1N4001 diodes would surely work there also.
Diodes D3, D4, D5, and D6 are actually a single bridge rectifier module I had laying around. I did not show it, but I did put a 1/4 Amp fuse on the primary side of the transformer. The reason why it's disconnected is at the bottom of the page. Since the bottom heater element is disconnected, I only have to worry about one element coming on.
That way, when the heater is on, the transmitter is on, and it goes off when the heater goes off. The 230 VAC is taken from the power connections to the heating element. The left section of the circuit is the power supply. An alternating current in the transmitting coil, induces a small alternating voltage across the receiving coil. At that small distance, I decided to hang a coil of wire on the garage side of the wall as a transmitter antenna, and another coil on the hall side as a receiving antenna, and use the pair like a very inefficient transformer. One side of the wall to the other is about 6 inches. The other side of that wall is the hallway in the house. The water heater is against the wall in the garage. There was also no convenient way to run wire into the house without drilling holes completely through a wall, which I didn’t want to do. Not pulling wire: The water heater is in the garage, but I want an indication in the house. Cost: Money was a little tight so I wanted to build it out of what I already had on hand.Ģ. The major factors driving the design choices were.ġ. It has also proven its worth by telling me when it has recovered from a shower so the next person has hot water for their shower. I built this to see how long my how water heater was running which would tell me about how much money I am spending on hot water.
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