Mole Deterrent Teardown

Posted on Feb 5, 2014

Having a very healthy population of moles in our vicinity, I logged onto eBay and bought four of the cheaply available (ultra )sonic mole deterrents for our garden lawns in the hope of persuading them to move elsewhere. Here`s a link to a couple of similar ads: eBay ad, eBay ad2. The basic idea is pretty simple and used with other animals too

Mole Deterrent Teardown
Click here to download the full size of the above Circuit.

the gadget emits an frequency that the animals in question (in this case the moles) aren`t keen on, so they move away from the area. Some are advertised as being ultrasonic mole deterrent , and some simply say sonic mole deterrent . Are they sonic or ultrasonic (ultrasonic means above the range of human hearing of which the upper limit is around 20kHz) What frequency do they actually work at Unfortunately the particular model purchased didn`t work for long enough (see below) to answer this question fully, but I`d say they did seem to make a difference initially. Further tests will have to be made on this front. Note that 2N2222 and 2N907 are used in the SPICE circuit as LTSpice doesn`t have models for 9014 or S8550, which are the actual parts used on the PCB. This matters little to the simulation (see below) as the circuit should work fine with most general purpose  bipolar transistors. Q1 and Q3 are responsible for the on/off pulses. If we start with Q1 turned on (via current through R1 into base), Q3 turned off, and either side of C1 at around 0V. R7 gradually charges up the right side of C1 (Q3b) until the voltage reaches around 500mV at which point Q3 will begin to turn on. When Q3 starts to turn on, Q4 and Q2 (BUZ_V) will also begin to turn on, activating the buzzer. Also the bottom of C2 will be pulled to ground, which will also pull Q1s base (Q1b) low, turning it off this will raise the voltage on the left (Q1c)...

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