Design of four-way wireless remote control switch

There are many wireless remote control products on the market, but the quality varies. Some of them still use LC oscillators, which have serious frequency drift and poor performance. This article introduces a wireless remote control component with stable performance and low price. The module operates at 315MHz and uses SAW resonator to stabilize the frequency. The frequency stability is very high. When the ambient temperature changes between -25℃-+85℃, the frequency drift is only 3ppm/degree. When it is used with the codec integrated PT2622/PT2722, it can realize remote control, telemetry, data acquisition, biological signal acquisition and other functions.

1 PT2262/2272

The encoding chip PT2262/2272 is a low-power, low-cost universal encoding/decoding circuit manufactured by Taiwan Pucheng Company using CMOS technology. It is a pair of wireless remote control transmitting/receiving chips with address and data encoding functions.

The transmitter chip PT2262 integrates the carrier oscillator, encoder and transmitter unit into one, making the transmitter circuit very simple. It has a wide operating voltage range (-15V-2.6V), where A0-A11 is the address pin, which is used for address encoding and can be set to "0", "1" or "f" (suspended). DO-D5 is the data input terminal. If one is "1", the code is sent, and it is pulled down internally. TE is the encoding start terminal, which is valid at low level. OSCl and OSC2 are the input and output terminals of the oscillation resistor respectively, and the external resistor determines the oscillation frequency. The set address code and data code are serially output from pin 17, which is usually at a low level, and can directly modulate the transmitter module to transmit the signal.

PT2272 usually has suffix output forms such as L4, L6 and M4. L4 and L6 are 4-way and 6-way self-latching outputs, and M4 is a 4-way non-latching output. The latching function means that when the transmission signal disappears, the data output end of PT2272 still maintains the original state until the next new signal input is received. The non-latching function of PT2272 means that when the transmission signal disappears, the corresponding data output bit of PT2272 becomes a low level, that is, the level of the data pin output is instantaneous, and corresponds to whether the transmitter is transmitting, which can be used for similar inching control.

2 Working principle of four-way remote control

2.1 Transmitter

The schematic diagram of the transmitting circuit is shown in Figure 1 (a).

Figure 1 Schematic diagram of the transmitting circuit

This part of the circuit is mainly composed of a 315MHz wireless data transmission module and an integrated coding PT2262. The schematic diagram of the wireless transmission module is shown in Figure 1 (b). It has a wide operating voltage range of 3-12V. When the voltage changes, the transmission frequency remains basically unchanged, and the receiving module matched with the transmission module can receive stably without any adjustment. When the transmission voltage is 3V, the transmission distance in an open area is about 20-50m, and the transmission power is relatively small; when the voltage is 5V, it is about 100-200m) and when the voltage is 9V, it is about 300-500m; when the transmission voltage is 12V, it is the best working voltage with a good transmission effect, the transmission current is about 60 mA, the transmission distance in an open area is 700-800m, and the transmission power is about 500mW. When the voltage is greater than 12V, the power consumption increases, and the effective transmission power is no longer significantly increased. The transmission module adopts ASK modulation to reduce power consumption. When the data signal stops, the transmission current drops to zero. The data signal can be connected to the input end of the DF transmission module with a resistor or directly, but not with a capacitor. Otherwise, the DF transmission module will not work properly. The data level should be close to the actual working voltage of the DF data module to obtain a higher modulation effect.

When no button is pressed, transistor Q is cut off, coding integrated IC1 is in power-off state, and wireless data transmission module does not transmit signal. When any button S1-S4 is pressed, transistor Q1 is turned on, coding integrated ICI starts to work, and it encodes according to the level of data input terminal Do-D3. The coding signal consists of: address code, data code, synchronization code to form a complete code word. The coded signal is modulated by wireless data transmission module V1 and transmitted to the surrounding space through the antenna. If the button is pressed all the time, the transmission module continuously transmits wireless signals. When the 17th pin of coding integrated ICI (PT2262) is low, the 315MHz high-frequency transmission circuit stops oscillating, so the high-frequency transmission circuit is completely controlled by the digital signal output from the 17th pin of PT2262 , thereby completing amplitude keying (ASK modulation) of the high-frequency circuit, which is equivalent to 100% amplitude modulation.

2.2 Receiving part

The circuit schematic diagram of the receiving part is shown in Figure 2 (a).

Figure 2 Schematic diagram of the receiving circuit.

This part of the circuit is mainly composed of a 315MHz wireless data receiving module, a decoding integrated PT2272, a D trigger 4013 and a relay circuit.

There are two types of 315MHz wireless data receiving modules: super regenerative receiving modules and super heterodyne receiving modules. The performance of super regenerative and super heterodyne circuits has their own advantages and disadvantages. The receiving sensitivity of the super regenerative receiving module is -105dBm, the anti-interference ability is poor, and the frequency is greatly affected by temperature drift. The copper core inductor with a skeleton is used to adjust the frequency to 315MHz and then seal it. Compared with the circuit that uses an adjustable capacitor to adjust the receiving frequency, the temperature, humidity stability and mechanical vibration resistance are greatly improved. The super heterodyne receiving module has strong anti-interference ability, extremely small self-radiation, and a mesh grounded copper foil shield on the back, which can reduce the leakage of self-oscillation and the intrusion of external interference signals; the waveform at the output end is relatively clean when there is no signal, and the interference signal is a short needle pulse, unlike the super regenerative receiving circuit that will produce dense noise waveforms, but there may be blocking when there is a strong signal at close range.

This production uses the PT2272 decoding chip (PT2272-M4) with the suffix M4. The operating voltage of PT2272 is 5V, of which A0-A11 are address pins, which are used for address encoding. They can be set to "0", "1" or "left open", but must be consistent with PT2262, otherwise it will not be decoded. D0--D3 are data pins. When the address code is consistent with PT2262, the data pin outputs a high level corresponding to the data end of PT2262. The latch type can only be converted when the next data is received. DIN is the data signal input terminal, which comes from the output terminal of the receiving module. OSCl and OSC2 are the input and output terminals of the oscillation resistor respectively, and the external resistor determines the oscillation frequency. VT is the decoding valid confirmation terminal, and the high level is valid.

Normally, when the wireless receiving module D1 does not receive the 315MHz signal in the space, it only outputs the interference signal, and the output terminals DO-D3 of the decoding integrated PT2272-M4 (IC1) are all low level.

When the wireless receiving module receives the 315MHz signal from the space, it outputs the control signal after amplification, frequency conversion, filtering and other processing, and sends it to the 14th pin of the decoding integrated IC1 for decoding. Only when the level state of the address end of PT2272 is consistent with the address end of PT2262 of the transmitting part, the corresponding data end will have a high level output. The address of this production is FFFFFF, that is, all are suspended. You can also change your own address code during production. The most important thing is not to interfere with each other. The bistable circuit composed of D flip-flop 4013, when the input end CK is a rising edge, the output end Q flips, and the output level controls the working state of the electrical appliance by controlling the on and off of the relay.

Figure 3 is the circuit diagram of the receiving part using PT2272L4.

If PT2272--M4 in Figure 2 (a) is changed to PT2272--L4, the four outputs will change from non-locked state to self-locked state. In this case, how can one of the outputs be changed from self-locked state to non-self-locked state? As shown in Figure 3, since the 17th pin of the receiving indication terminal outputs a high level only when the receiving decoding is correct, it turns to a low level when the transmitter is not working. When the coded signal is transmitted, the 13th pin locks the output at a low level, and the 17th pin is at a commercial level at the same time, D5 is cut off, and the output of the 13th pin is connected to a high level output; when the coded transmitter stops transmitting, the decoder does not receive the correct signal, although the 13th pin has been locked to a high level, the 17th pin turns to a low level, making the diode D5 forward biased, and the high level output of the 13th pin through R? is pulled down to below 0.7V. If D uses a germanium diode 2AP9, the output level will be lower.

Therefore, the output interface is low level output when not decoded, that is, it is in the unlocked state. Therefore, if the enzyme PT2272--M4 in Figure 2 (a) is changed to Pr2272--L4, and the schematic diagram 2 (a) is changed to Figure 3 accordingly, the same function can be achieved, that is, the four-way unlocked state. If a certain path is changed to the unlocked state, the corresponding diode is removed. For example, by removing D5, the non-self-locking output of the 13th pin of PT2272--L4 is changed to a locked output.

3Installation and debugging

This circuit uses DF wireless data transceiver module and codec integrated PT2262/PT2272-M4. The receiving part T1 is 6V power supply , and the electrical appliance can be selected according to the power of the control appliance. There is no special requirement for other components. Solder the components firmly and accurately on the circuit board engraved according to the schematic diagram, and connect the power line and signal line between the circuit board and the wireless transmission/reception module.

After the circuit is made and confirmed to be correct, you can connect the power supply for debugging. Do not connect the electrical appliances first. Press the button of the transmitting part. If you hear the relay action is reliable, then connect the electrical appliances. At this time, if the relay is in good quality, it will generally work normally.

In order to reduce the size of the transmitting circuit, a button battery or a special battery for the remote control can be used. Different voltages will result in different remote control distances. The receiving circuit can be installed in a plastic box. Four relays are four switches, thus forming a four-way remote control switch.