Homemade hand dryer (dryer)

The induction automatic hand dryer used in public restrooms has a simple principle. I have made one before. Its circuit is divided into two parts: the main circuit and the control circuit. Now I will introduce it to you readers.

The main circuit consists of 1500W electric furnace wire, 20A thyristor (crystal tube) and blower. The control circuit is connected with them through relays to form a complete machine. See the attached figure.

The core of the control circuit is the "active infrared sensor". The two infrared diodes for transmission and reception are installed in parallel near the air outlet, about 10 cm apart. The distance and direction should be fine-tuned. The infrared rays emitted by the transmitting tube L1 are reflected by the hand and are received by the receiving tube L2.

There are two NE555s in the figure (NE556 can be used instead). The first IC1 constitutes a square wave generator with a frequency of about 2kHz. Its pulses are output in two ways: the first way is added to the infrared transmitting tube L1 through a 100Ω resistor, and the second way is sent to the first input terminal of the NAND gate through a 22kΩ resistor. After the infrared receiving tube L2 receives the signal, it is coupled to the first 9014 transistor through a 2.2μF capacitor for amplification. The amplified output signal is sent to the second foot of the 74LS00, which is the second input terminal of the NAND gate. Only when the two input signals of the NAND gate are in phase, it will have an output (it can be seen that the interference signal is difficult to work here). The pulse signal output from the third foot of the NAND gate is coupled to the voltage doubler rectifier through a 10μF capacitor. The positive DC voltage output by the rectifier causes the second foot of the second IC2 to be triggered by a low level instantaneously. IC2 is connected in a monostable state. After the low level is triggered, a high level will be output from pin ③ and maintained for about 20 seconds (the length of time is determined by the 51kΩ resistor and the 330μF capacitor). This is called a delay circuit, and its purpose is to unify the time of each hand drying.

The output of the delay circuit is coupled through a 1kΩ resistor. It is sent to the base of the third 9014 transistor. When the base is at a high level, the transistor is turned on. The collector current flows through the relay J, and the two pairs of contacts J1 and J2 are attracted. The bidirectional thyristor SCR is turned on because the control electrode and the anode are connected through the 1kΩ resistor. The 1500W electric furnace wire is energized and heated. At the same time, the blower motor M is also powered and blows air. The structure of this blower can refer to the "hair dryer" used for shampooing. The coil voltage of the relay J is 24v, and the contact current is 10A (250VAC) enough.

As mentioned above, the NAND gate is an important circuit for anti-interference, because the probability that the interference signal appears in both the transmitting and receiving signals and has the same phase is extremely small. In addition, a 10μF capacitor is connected to the second pin of the 555 for anti-interference, which can be increased to 220μF. The oscillation frequency of the first IC1555 is determined by the 22kΩ resistor and the 0.022μF capacitor, which is about 2kHz and can be changed.

The infrared transmitting tube L1 can be disassembled from an old TV remote control, so you don't have to buy it. But you need to buy a new infrared receiving tube L2. It uses 620kΩ, and it is more sensitive after the resistor is reverse biased. Some people say that the transmitting tube can also be used as a receiving tube, so you can try it.