I forget where I found this thing. It was either in the garbage or at a garage sale. Pressed into the plastic are the words: "Insect and rodent control equipment. . . model number PAC-1C. . . USA patent number 4,802,057" The main thing this circuit demonstrates is how to get a low voltage supply from the AC mains without using a transformer. Weather it actually gets rid of pests is another question entirely.
WARNING: This circuit is AC line powered and contains voltages and currents which can KILL if you are not careful. Charged capacitors will SURPRISE YOU! They can hold a lethal charge for hours! If you don't know much about working with line voltages or if you aren't crazy (like me) then DO NOT attempt to construct this circuit. I CANNOT BE RESPONSIBLE if you electrocute yourself to death! That said, let's have some fun!
R1 100R, 1/2W
R2 1k, 1/4W
R3 2k2, 1/4W
C1 470n, 250V polyester
C2 220u, 25V
RV1 100nF, 50V polyester
L1 ? see text
RC1 100nF, 600V + 100R "Quencharc"
CR1, CR2 1N4004 "Current Rectifiers"
Q1 SC141D, 400V, 8A TRIAC
U1 MOC3021 400V TRIAC output optocoupler
U2 ETC551, Unknown, see text
The 120VAC mains is taken through R1 and C1 to limit current. Power is taken by CR1 during one half cycle and through CR2 during the other half. CR1 is necessary to keep power moving through CR2 by preventing C1 from charging only in one direction. The DC pulses from CR2 are smoothed by C2 to produce around 5VDC to power the ICs.
U2 is referenced to the AC line at pin 8 (See further text). The outputs at pins 2&7 go low alternately, flashing the indicator LED and the internal LED of U1. The internal photoTRIAC of U1 then is turned on and off with the flashes of the internal LED.
When U1 is switched on, gate current is provided to Q1 through the 2.2:1 voltage divider formed by R2 and R3 causing it also to turn on. Q1 switches current into inductor L1. Snubber network RC1 assures turnoff of Q1 when gate current ceases at the end of the present half cycle and also protects it from any back EMF generated by L1.
L1 is many thousands of turns of fine wire around what appears to be an iron slug. I cannot measure the inductance of L1 due to the fact that I cannot afford an LCR meter. If anyone would be willing to donate one to my cause, I would appreciate it very much. The round slug measures approximately 1/4" by 1" long and is connected to one of the mains terminals. Apparently it doesn't matter which one because the plug is not keyed to go in a certain way. According to the patent, the purpose of this is to use the house wiring as a sort of antenna to carry the "signal" and make it less appealing to pests. Like I said before, I can't be sure weather this actually deters any pests. When it's plugged in, though, I swear there are less spiders around. Probably just the placebo effect though.
I was unable to find any data on U2. From what I can gather from the circuit, it appears to be a 1 second timer that is referenced to the AC line. It could also be some sort of custom IC that does this as well as regulates the voltage. According to the patent, it is supposed to turn and off once a second for a while, then be completely off for a while and then start pulsing again, which this IC seems to do. This would lend credence to the theory of it being some kind of programmable or custom IC.
All drawings were made with XCircuit
(opencircuitdesign.com/xcircuit), a platform independent, X-Windows
application.