Remote control is a kind of device used for remote control of machinery. Modern remote control is mainly composed of integrated circuit board and buttons used to generate different messages. Electronic enthusiasts can choose special integrated circuit board to make remote control circuit, but mastering the principles of some common remote control circuits is very helpful to improve their own technology. Single channel, single user remote control circuit is the simplest one in remote control circuit, which is usually used for light and sound control.

1、 Light control circuit

Figure 1 is a light control circuit composed of 555 time base circuit. Because it does not need special transmitter, it belongs to telemetry circuit. Photodiode VD1 is used for light detection and conversion. Photodiodes with different performances can be used to convert infrared or visible light into electrical signals. In IC1, a Schmidt trigger composed of NE555 is used to shape and amplify the received optical signal to drive the follow-up circuit. The driving current is up to 200mA, which can directly drive the relay or micro motor. The circuit is positive logic control, that is, ICL output high level when there is light, output low level when there is no light. If negative logic control is needed, VDL and R1 can be exchanged. C1, R2 integral circuit is to filter out the interference pulse and prevent misoperation. The range of power supply voltage is 5V-12V. When debugging, adjust R1 according to the need to make the circuit have proper sensitivity. The circuit can be used for infrared detection, anti-theft alarm or danger forbidden alarm; if the optical detection head of the circuit detects the production process, its output is connected to the electronic counter, and it can also be used for the detection of the number of products on the production line and the number of paper on the printing machine.

2、 Voice control circuit

Figure 2 is a voice control circuit with dual operational amplifier lm158 as the core, which is also a telemetry circuit in essence. Ic1-1 forms a 20 times voltage amplifier, which amplifies the voice control signal picked up by the micro electret microphone to a certain amplitude. After VD1 rectification, C3 and R5 filtering, it is sent to the voltage comparator composed of ic1-2. The reference voltage of the voltage comparator is taken from the voltage dividing points of R6 and R7, about 0.8V; When there is a voice control signal, the voltage of the fifth pin is greater than the reference voltage of the sixth pin, out = 9V. During debugging, adjusting R3 can change the voltage gain of ic1-1, so that the receiving sensitivity is appropriate; R7 can also be adjusted to change the comparison level (reference voltage) of the voltage regulator, so as to meet the requirements of sensitivity and anti-interference (R7 is increased, the anti-interference ability is strengthened, but the sensitivity is low). Power supply voltage range 5 ~ 15V, IC1 can also choose other types of op amp. Generally speaking, Op Amp can drive more than ten Ma load. Voice control signals can be applause, whistling, knocking, etc. The circuit can be used for voice switch.

3、 Ultrasonic remote control transmitting / receiving circuit

As shown in Figure 3, the ultrasonic emission is composed of 555 timers, in which RP, R1 and C1 are timing elements, and the oscillation period is calculated by the formula (let W1 = 15.3k Ω).

Adjust W1 to make the oscillation frequency 40KHz, so the ③ pin of 555 outputs 40KHz square wave, and drives the ultrasonic transmitter T40 through T1. The ultrasonic receiver is R40, which must be used in pairs with T40. The type and working principle of the receiving circuit are the same as those in Figure 2, but the difference is that icl-1 in this figure forms a 40KHz double-T network frequency selective amplifier; C4, C5, VDL and VD2 are double voltage detection. The ic1-2 voltage comparator is the same as Figure 2.

Usually, the distance of ultrasonic remote control is 2m ~ 10m, which can be adjusted by ICL_ L gain resistor R3 and ic1-2 compare the level resistor, both sensitivity and anti-interference performance. This circuit can be used for burglar alarm or danger forbidden alarm.

4、 Infrared remote control transmitting / receiving circuit

The infrared remote control transmitting and receiving circuit is shown in Figure 4. The transmitting circuit is basically the same as that in Figure 3. It is also a multivibrator composed of 555, except that the oscillating square wave drives the infrared transmitting tube D1, whose oscillation frequency is 35kHz ~ 40KHz, which is set by RP. The receiving circuit uses ASIC CX20106, the receiving center frequency f0 = 30kHz ~ 60KHZ, but it must be consistent with the frequency of the transmitter, set by R4, when R4 is 220K Ω, F0 is about 38kHz. The signal received by the infrared receiving tube ph302 enters IC2 from ①, and is output by pin ⑦ after amplification and demodulation. When debugging, first adjust the receiving circuit R4, so that the receiving frequency is consistent with the transmitting frequency; then adjust the R3, so that the circuit has the appropriate sensitivity. The remote control distance of the circuit is 8m ~ 10m, which can be used for anti-theft alarm; if the receiving output end is connected with an electronic counter, it can be used for product quantity detection on the production line; if the receiving output end drives the triode, then the triode drives the relay, the relay drives the solenoid valve, and the solenoid valve is used to control the faucet, which constitutes the automatic controller of tap water. The emitter is installed near the tap. The emitter can be either body sensing or photoelectric. As long as the hand is close to the tap, the tap valve can be opened. Of course, it can also be made into automatic hand washing dryer.

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