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Schematic diagram of a simple Cat repellent device. It is based on a PIC12F615 microcontroller that has on-board electronics to generate a Pulse Width Modulation (PWM) signal. Because of that hardware, hardly any external components are needed
The PIC12F615 supports a PWM bridge mode which means that when one output goes high, the other output goes low. When connecting both outputs to a piezo buzzer, the voltage swing will be twice the battery voltage and so doubling the output signal of the piezo buzzers.
Attached you find the schematic diagram, a screenshot of the bridge PWM signal when no buzzer is connected and a screenshot of the signal over the buzzer showing the double voltage.
The mini PIR module has all electronics integrated in the PIR detector and can operate on a supply voltage of 2.7 to 12 Volt.
Some measurements on the power consumption of the device. When in sleep mode the PIC hardly uses any power but the PIR is drawing a continuous current of 16 uA. When the PIC and buzzers are active, the average total current is about 4.4 mA. The power delivered by the solar panel should be sufficient to keep the batteries charged.