Mosquito repeller

Consider the operation of the device. The diode VD1 is necessary to protect against improper power connection to the circuit. The device is powered by galvanic cells +1.5 V (supply voltage can be increased to +9 V). With increasing voltage, the radiation power of the device increases. The sound-reproducing element of the device is a ZP-1 piezo emitter (ZP-3, ZP-22) or any other, for example, from a wristwatch. Resistors R2 ... R4 and R5, R6 set the operating point of transistor VT1 and VT2. When voltage is applied to VT1, C1 is charged, a pulse from C1 briefly opens VT2, VT2 charges C2, which briefly opens VT1, and the cycle of work repeats again. The frequency of the generator depends on the values ​​of capacitances C1 and C2 and the resistance R6. You can turn on several more emitters in series with BQ1, then the output power will increase.