Remote control for computer. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Microcontrollers

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The described simple IR receiver and a small driver program allow the computer to "understand" the commands given from the remote control (RC) from a conventional TV. How to use this opportunity, we leave it to the reader to decide. It can be a remote control of a music CD player program, a wireless joystick for computer games and much more.

Schematic diagram of the receiver of IR remote control signals built into the computer is shown in fig. 1. The pulses received by the VD1 photodiode are fed to the input of the DA1 microcircuit, which filters and amplifies them. The output signal through the inverter DD1.1 is fed to the input IRQ10 bus ISA computer. Each rising edge is interpreted by the computer as an interrupt request and processes it by calling the procedure located at the address specified in the interrupt vector 72H. The duration of the pulses sent by the remote control is sufficient for the processor to respond to an interrupt and it is not necessary to "stretch" them additionally.

The receiver is mounted on two printed circuit boards. The first one (Fig. 2) has a VD1 photodiode, a DA1 microcircuit, capacitors C1-C4 and a resistor R1. It is placed on the front panel inside the computer system unit (the method of attachment does not matter), covered with a metal screen connected to a common wire. Opposite the VD1 photodiode, a hole is drilled in the computer case for the passage of IR rays, which can be closed with a red organic glass light filter.

On the second board (Fig. 3), the DD1 chip and capacitors C5, C6 are mounted. It is necessary to maintain the length of the board (48 mm) and the distances of the contact pads from its left edge indicated in the figure as accurately as possible. This will ensure a reliable connection between the receiver and the computer. The board is inserted into the additional (short) part of any free ISA slot in such a way that the arrow on it points towards the front panel. Contact pads of the same name 1-3 of both boards are interconnected by a ribbon cable or a bundle of three ordinary wires.

The boards are designed for the installation of oxide capacitors K50-35, K50-16, ceramic K10-17 or any other small-sized resistor MLT-0,125. Chip K1056UP1 (DA1) can be replaced by KR1084UI1 or imported TBA2800 (taking into account differences in pinout). Any open collector inverter is suitable as an element of DD1.1. The receiver does not require tuning, but sometimes it is useful to choose the capacitor C3, achieving maximum range.

The table shows the source text of the RCU.COM program - the remote control driver on the KR1506HL1 chip for 3USTST TVs, described in the book by Elyashkevich S.A. "Color stationary TVs and their repair" (M .: Radio and communication, 1980). When you press any button, the remote control transmits a series of 14 IR pulses, the duration of the intervals between which is encoded by the command being sent. The receiver can work with others, including imported remote controls, but you will have to write an appropriate driver for them.

RCU.COM works with the MS DOS operating system and is loaded into the computer's memory resident, allowing application programs to receive and execute commands sent from the console. The program consists of three parts. The first one, beginning with the init label, prints a message to the screen that the driver is loading, initializes the interrupt handlers, and leaves them resident in memory.

The second part is the IRQ10 hardware interrupt handler, which corresponds to the 72H vector. The computer executes it after receiving each pulse from the remote control, fills the buffer buf with a sequence of values ​​for the duration of the intervals between pulses and counts them. Having received the entire series, the handler sets the code readiness flag in the pe cell.

In order to receive the received command, the application program must trigger software interrupt 2FH. It is he who processes the third part of the driver in question. Depending on the code loaded into the AX register before the call, it works differently.

(click to enlarge)

This interrupt performs its main function when called with code 0E401H. In the DX register, it returns the received code to the application program, and in AX, its ready flag. The zero value of the ready flag indicates that no new command has been accepted since the last interrupt call and the code in DX cannot be used. A flag equal to 1 indicates that the command has been received and the need to read from the DX and store its code. This must be done, as the code may change before the next call.

The call with the code 0E400H is used to check if the remote control driver is loaded into RAM. If so, the code 0E4FFH will be returned in the AX register. Calling the 2FH interrupt with other codes results in the execution of the "old" handler that was in effect before the RCU.COM program was loaded.

Author: S.Kuleshov, Kurgan

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