Design of simple leakage alarm

The two alarms introduced here have simple circuits and sensitive triggering. They can be directly installed in modular sockets and are suitable for leakage alarms of household appliances. They are cheap and easy to make.
Working Principle The circuits of these two alarms are shown in Figures 1 (a) and (b) respectively (click to download the schematic diagram). Figure (a) is a leakage alarm made with a CMOS six-phase inverter CD4069. Normally, the audio oscillator composed of gate A, gate B, R2, and YD does not make any sound when there is no current passing through it. When an appliance with a leakage shell is inserted into a three-hole socket, the leakage current flows from the live wire of the power supply through the appliance shell to the ground wire jack of the three-hole socket, and then returns to the neutral wire of the power supply through the alarm to form a loop. The pulsating current after the leakage current is stepped down by R1 and rectified by VD causes the alarm to sound. The leakage alarm current of this circuit is less than 0.3mA. Figure (b) is a leakage alarm made with a CW9300 music IC. Since R1 and VT form a high-sensitivity trigger circuit, the alarm has a high sensitivity and its leakage alarm current is less than 10uA. The working voltage of the music IC is supplied after R2 steps down, VD rectifies, and C filters. Since the voltage is taken from the live wire of the 220V mains, compared with some alarm circuits that rely on leakage current and voltage to maintain the IC sound, not only is the alarm volume larger, but it also overcomes the disadvantage that the volume of the above circuit changes with the leakage current. Component selection and production Components are selected according to the schematic diagram. When making, a circuit can be selected according to the specific situation. Cut off the two electrodes of a two-hole socket at the lower end of the modular socket to accommodate the circuit components and install them in the empty space. After installation, a 200Ω resistor can be used, one end connected to the live wire of the power supply and the other end connected to the ground end of the socket to simulate the leakage test. The circuit should work normally. The withstand voltage of the diode in the figure should be >400V, YD can be Φ27mm, the β of the transistor VT is ≥100, and the resistors are all 1/8W.