Touch doorbell circuit diagram

The touch doorbell introduced in this article uses touch instead of mechanical switches. It is simple, reliable, practical and interesting.

Working principle: The circuit schematic is shown in the figure. The 555 time base integrated circuit works in a monostable state, and the ③ and ⑦ pins are usually low level . When touching the metal sensor piece M with your hand, the human body's induction signal is added to the 555 time base integrated circuit through a 0.1μF capacitor. Pin ② causes the circuit to flip into a temporary stable state. At this time, pin ③ outputs a high level and is directly added to the trigger end of the doorbell chip. The chip is triggered and drives the speaker to sound through the transistor. At the same time, pin ⑦ also becomes high level, and the power supply charges the 4.7μF capacitor through the 100KΩ resistor. When the voltage on the capacitor is charged to 2/3 of the power supply voltage, the circuit flips again, the temporary steady state ends, and pin ③ becomes low again. flat. When M is touched again, the above working process starts over again. So every time M is touched, the doorbell is triggered. ③The 0.01μF capacitor on the pin is an anti-interference capacitor, which can prevent the doorbell from being accidentally triggered.

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Touch doorbell circuit

Component selection and production: The doorbell chip of this circuit uses the "Ding Dong" (HL9300) chip. Every time it is triggered, even after the ③ pin becomes low level, it can still make three consecutive "Ding Dong" sounds. If you choose a chip (such as a music chip) that requires the trigger terminal to be always at a high level before it can sound, you should appropriately adjust the resistor-capacitance time constant on pin ⑦ to adjust the temporary steady state time, so that the high level of pin ③ is sufficient Make the chip emit a complete piece of music before turning to low level. In addition, the base potential of the push transistor of the doorbell chip should be measured when the doorbell chip is powered on. If it is low level , then an NPN transistor should be used as the push tube. The purpose is to prevent static dynamic consumption and extend the battery life. When the lead of the touch piece is too long, it is best to use a shielded wire and ground the shield. This circuit is simple to make and can work normally as long as it is installed correctly. This circuit can also be expanded into practical circuits such as touch switches and touch alarms.