Design and production of a simple remote control circuit

A remote control is a device used to remotely control machinery. Modern remote controls are mainly composed of integrated circuit boards and buttons used to generate different messages. Electronics enthusiasts can use dedicated integrated circuit boards to make remote control circuits, but mastering the principles of some commonly used remote control circuits is very helpful in improving their own skills. Single-channel, single-user remote control circuits are the simplest type of remote control circuits, and the circuit is usually used for light and sound control.

1. Light control circuit

Figure 1 shows a light control circuit using a 555 time base circuit. Since it does not require a dedicated transmitter, it belongs to a telemetry circuit. The photodiode VD1 is used for light detection and conversion. Photodiodes with different performances can be used as needed to convert infrared light or visible light into electrical signals. IC1 uses NE555 to form a Schmitt trigger to shape and power amplify the received light signal to drive the subsequent circuit. The drive current is 200mA, which can directly drive a relay or a micro motor. This circuit is positive logic control, that is, ICl outputs a high level when there is light, and outputs a low level when there is no light. If negative logic control is required, just swap VDl and R1. The C1 and R2 integration circuits filter out interference pulses to prevent false operations. The power supply voltage range is 5V to 12V. During debugging, adjust R1 as needed to make the circuit have appropriate sensitivity. This circuit can be used for infrared detection, anti-theft alarm or dangerous entry alarm; if the light detection head of this circuit detects the production process, the output is connected to an electronic counter, and it can also be used to generate online product quantity detection and printing press paper feed quantity detection.

2. Voice control circuit

Figure 2 is a voice control circuit based on the dual op amp LM158, which is also a telemetry circuit in essence. IC1-1, a 20-fold voltage amplifier, amplifies the voice control signal picked up by the miniature electret microphone to a certain amplitude, and then sends it to the voltage comparator composed of IC1-2 after rectification by VD1, filtering by C3 and R5. The reference voltage of the voltage comparator is taken from the voltage divider point of R6 and R7, which is about 0.8V. When there is no voice control signal, the voltage of IC15 is 0V, which is less than the reference voltage of pin 6, and the output OUT=0; when there is a voice control signal, the voltage of pin 5 is greater than the reference voltage of pin 6, and OUT=9V. During debugging, adjusting R3 can change the voltage gain of IC1-1 to make the receiving sensitivity suitable:

R7 can also be adjusted to change the comparison level (reference voltage) of the voltage regulator to take into account the requirements of sensitivity and anti-interference (increasing R7 will enhance the anti-interference ability, but reduce the sensitivity). The power supply voltage range is 5~15V, and IC1 can also use other types of op amps. Generally speaking, the op amp can drive a load of more than ten milliamperes. The voice control signal can be clapping, whistling, knocking, etc. This circuit can be used for voice-controlled switches.

3. Ultrasonic remote control transmitting/receiving circuit

As shown in Figure 3, the ultrasonic transmitter is composed of a 555 timer to form a multivibrator, where RP, R1, and C1 are timing components, and the oscillation period is calculated by the formula (assuming W1 = 15.3kΩ).

Adjust W1 to make the oscillation frequency 40kHz, so that the 555's ③ pin outputs a 40kHz square wave, which drives the ultrasonic transmitter T40 through T1.

The ultrasonic receiving head is R40, which must be used in pairs with T40. The receiving circuit type and working principle are the same as those in Figure 2, except that ICl-1 in this figure constitutes a 40kHz double-T network frequency selection amplifier; C4, C5, VDl, and VD2 are voltage doubler detectors. IC1-2 voltage comparator is the same as in Figure 2.

Usually the ultrasonic remote control distance is 2m~10m, and the sensitivity and anti-interference performance can be taken into account by adjusting the gain resistor R3 of ICl_1 and the comparison level resistor of IC1-2. This circuit can be used for anti-theft alarm or dangerous entry alarm.

4. Infrared remote control transmitting/receiving circuit

The infrared remote control transmitting and receiving circuits are shown in Figure 4. The transmitting circuit is basically the same as Figure 3, and is also a multivibrator composed of 555, except that the oscillating square wave drives the infrared transmitting tube D1 with an oscillation frequency of 35kHz~40kHz, which is adjusted by RP. The receiving circuit uses a dedicated integrated circuit CX20106, and the receiving center frequency f0=30kHz~60kHz, but it must be consistent with the transmitting end frequency, which is adjusted by R4. When R4 is 220kΩ, f0 is about 38kHz. The signal received by the infrared receiving tube PH302 enters IC2 from ①, and is output from pin ⑦ after amplification and demodulation. During debugging, first adjust the receiving circuit R4 to make the receiving frequency consistent with the transmitting frequency; then adjust R3 to make the circuit have appropriate sensitivity. The remote control distance of this circuit is 8m~10m, which can be used for anti-theft alarm; if the receiving output end is connected to an electronic counter, it can be used for product quantity detection on the production line; if the receiving output end drives the transistor, and then the transistor drives the relay, the relay drives the solenoid valve, and the solenoid valve is used to control the faucet, it constitutes a tap water automatic controller. The transmitter is installed near the tap. It can be a human body induction type or a photoelectric type. As long as the hand is close to the tap, the tap valve can be opened. Of course, it can also be made into an automatic hand washing dryer.