PC infrared interface

Infrared communication is a cheap, short-range, wire-free, low-power and highly confidential communication solution. It is mainly used in wireless data transmission in PCs, but it has gradually begun to be used in wireless network access and near-field communication. It has been applied in distance remote control home appliances. In view of the many benefits of infrared communication, almost all current motherboards provide infrared interfaces so that users can use them to communicate with devices with infrared interfaces, such as laptops, printers, Modems, PDAs, mobile phones, etc. However, the computer motherboard only provides an infrared interface and does not provide a complete transmitting and receiving device, so users still need to purchase an infrared connector when they want to use infrared communication. There are currently few commercialized connectors on the market. Here are three DIY solutions for your reference. 1. Motherboard infrared interface: The infrared interface on the motherboard is mostly a 5-pin socket, and its pin definitions are: 1. IRTX (Infrared Transmit, infrared transmission); 2. GND (power ground); 3. IRRX (Infrared) Receive, infrared reception); 4. NC (undefined); 5. VCC (power supply positive). According to the "Asynchronous Serial Communication Standard" information provided by IRDA (Infrared Data Association), the IRTX pin can provide an output current of >6.0mA, while the IRRX pin can absorb the input signal by absorbing <1.5mA current. react. The data also shows that the transmitting part of the infrared interface has transmitted the data to a 38kHz carrier wave, and the receiving part will perform signal separation processing, so there is no need to consider the carrier wave and separation circuit when making the interface circuit. 2. Standard infrared interface: The picture below shows the standard solution for infrared communication circuit provided by IRDA. The infrared emission circuit is composed of infrared emission tube L2 and current limiting resistor R2. When the output terminal IRTX of the infrared interface of the motherboard outputs the modulated electrical pulse signal, the infrared transmitting tube converts the electrical pulse signal into an infrared light signal and emits it. Resistor R2 limits the current to prevent excessive current from damaging the infrared tube. When the resistance of R2 is smaller, the current passing through the infrared tube is greater. The emission power of the infrared tube also increases with the increase of current, and the emission distance is farther. However, the resistance of R2 cannot be too small, otherwise it will be damaged. Infrared tube or motherboard infrared interface! The infrared receiving circuit is composed of infrared receiving tube L1 and sampling resistor R1. When the infrared receiving tube receives an infrared light signal, its reverse resistance will change accordingly with the intensity of the light signal. According to Ohm's law, it can be known that the current passing through the infrared receiving tube L1 and resistor R1 will also change accordingly, and in The voltage at both ends of the sampling resistor also changes accordingly, and this changed voltage is input to the host through the input terminal IRRX of the infrared interface of the motherboard. Since different infrared receiving tubes have different electrical parameters, the resistance of the sampling resistor R1 needs to be adjusted within a certain range according to the actual situation. This circuit is IRDA's standard solution and can be used by general DIYers. Although the circuit is very simple, its performance is still good. I used this circuit to connect to my laptop, and the transmission speed can reach 57.6Kbps without any bit errors! 3. Expanded infrared interface: The figure below shows the infrared communication circuit expansion solution provided by IRDA. This circuit is based on the standard circuit and adds an anti-interference circuit and a transmit power increasing circuit. The anti-interference circuit is composed of resistor R4, electrolytic capacitors E1 and E2, and monolithic capacitors C2 and C3. It is mainly used to filter out interference waves in the PC power supply. If your machine's power supply is of good quality, you can omit this part of the circuit. The circuit to increase the transmit power consists of resistors R2, R3, power transistor P1 and capacitor C1. The function of C1 is to improve the waveform of the output signal, and the transistor amplifies the output current to increase the transmit power. 4. Enhanced infrared interface: The picture below shows the infrared communication circuit enhancement scheme compiled by me based on experiments. The main improvement in this circuit is that the transmitting part uses tube amplification, which further improves the transmitting power; while the receiving part uses triodes to amplify the received signal, improving the receiving sensitivity. The working principle can be referred to the above description. 5. System settings: System settings are divided into two parts: BIOS and operating system. Turn on the infrared interface in the BIOS. The interface generally uses the same address and interrupt as COM2, so after the infrared interface is turned on, the COM2 port will be unusable. If you have other devices using the COM2 port, be careful! The settings of the operating system are generally after the system finds the infrared interface. The setting will be completed automatically. Users should note that when using the infrared interface, remember to turn on the infrared interface, that is, double-click "Infrared Monitor" and select "Enable Infrared Interface" in "Options". I believe everyone knows it, so I won’t say more. 6. Component selection: The selection of components is mainly the testing of transmitting tubes and receiving tubes. 1. Test the infrared transmitting tube: The infrared transmitting tube is actually a special diode. Use the resistance range of a multimeter to measure it. The reverse resistance of the transmitting tube is usually infinite, and the forward resistance is generally about 500K. If you have a laptop, you can connect the IRTX and GND lines from the infrared interface of the PC. IRTX is connected to the positive electrode of the transmitter, and GND is connected.