Infrared light controlled automatic faucet

This infrared light-controlled automatic faucet has strong anti-interference ability, few components, simple circuit and low cost. If you are interested, you may want to give it a try.

The control process of infrared light-controlled automatic faucet: when a hand or object approaches the automatic faucet, the infrared light emitted by the infrared transmitting phototube is reflected by the hand or object to the infrared receiving phototube. The receiving phototube automatically converts the reflected light signal into an electrical signal, which is further amplified and shaped by the subsequent circuit. Finally, the drive circuit controls the solenoid valve to open the water source. When the hand or object leaves the automatic faucet, the receiving phototube does not receive the reflected light signal, and the drive circuit disconnects the power supply of the solenoid valve and closes the water source.

1. Circuit Working Principle

There are two common ways to provide working power to the photoelectric transmitting tube: one is to use a DC power supply. The advantages of this power supply method are simple circuit and low cost, but it will cause malfunction to the interference light source, and may be completely out of control under strong light, and the working reliability is poor. The other is to use a 38KHz pulse power supply. The photoelectric receiving tube receives the 38KHz signal, amplifies and shapes it through the subsequent circuit, and extracts the correct approach signal, which can effectively eliminate the problems caused by light source interference, but the circuit is complex, the cost is high, the volume is large, and the installation location is limited.

The circuit is shown in the figure below. The working power supply provided to the photoelectric transmitting tube in this circuit uses 50Hz AC power instead of 38KHz pulse power. The 50Hz half-wave pulse output by the receiving photoelectric tube is a quasi-AC signal, which can effectively filter out the interference of slowly changing light sources, improve the anti-interference performance, and simplify the circuit.

In the circuit, the power supply adopts a transformer step-down method, and the voltage added to the faucet is only 12V, which does not pose a safety hazard to the user. The 12V AC voltage is limited by R3 on one path, and the 50Hz AC power is provided to the transmitting photoelectric tube D6 for operation; the other path is stabilized to 12V by a full-wave rectifier voltage regulator circuit for subsequent circuit operation. When the receiving photoelectric tube D7 receives a weak human body reflected light signal, it converts it into a half-wave pulsating DC signal, which is coupled to the positive input terminal (pin 3) of the first-stage operational amplifier through C4 for amplification, and a small bias voltage is added to the negative input terminal of pin 2 to prevent small signal interference. The amplified signal output from pin 3 is shaped and smoothed by R8, D5, and C5 to become a DC signal, and is sent to the positive input of the second-stage op amp at pin 5 as a voltage comparator. The flip voltage of the comparator is determined by the voltage divider value of R1O and R11 connected to the negative input of the second-stage op amp at pin 6. Rl2 is the positive feedback resistor of the op amp, and together with C5 and C6, it forms a delay circuit to prevent the signal from being interrupted during human activities and causing intermittent water supply. When the second-stage op amp pin 7 outputs a high level, the transistor Q1 is turned on, controlling the solenoid valve DCF to open the water source.

The figure on the right is a structural diagram for reference. The solenoid valve, circuit board and other components are small in size. When making them simply, you can use a 70mm long, 50mm PVC pipe to make the shell.

2. Production precautions

1. The infrared transmitting tube and the receiving tube should not be installed too close to each other. Optical isolation should be done between them to prevent mutual interference and malfunction;

2. The photosensitive transparent window at the front end of the infrared transmitting tube and the receiving tube can be made of black epoxy resin material, which can better prevent interference from visible light, or it can be made of dark red plexiglass; 3. DCF uses an AC voltage of 12V and a power of about 5 watts of solenoid valve, which can be replaced by a washing machine water supply solenoid valve; the transformer should have a power of 8 watts or more, or you can directly use a commercially available small-scale voltage-stabilized power supply and remove the rectification and voltage-stabilization part.