AVR-Based Serial Port IR Receiver
This is a simple IR receiver circuit which plugs into a serial port of a computer.
Okay, there are many other circuits of this kind, and most of them are even
simpler, but this circuit has two major advantages: (1) it uses an Atmel AVR
RISC microcontroller (an AT90S2313) instead of the usual PIC microcontroller
and (2) it uses a Maxim MAX232 for the generation of valid RS232 levels.
Advantage 1 is, of course, only valid for all those AVR addicts which have
this device (and the corresponding programmer) ready at hand and don't care
about PICs and PIC programmers. Advantage 2 comes into play if the IR receiver
has to placed at a great distance from the computer; the MAX232 is more likely
to deliver valid signals over bigger distances than cheaper solutions.
The IR receiver can receive it's +5V supply voltage from the keyboard or mouse
connector of the computer (either from an unsued PS/2 port or via a pass-thru
adaptor). If the IR interface is placed at a great distance from the computer,
I power it with an external stabilized 5V DC power supply instead of the PS/2
The interface communicates at 19200 baud, unidirectionally (that means, it
only transmits data and does not care anything about data which the computer
send), without flow control. For every level transistion in the demodulated
IR signal, it transmits a single byte which corresponds to the time since the
previous transistion, capping off at a value of 255. It works reliable with
a Sony remote control (using the special Sony protocol), and I have also succesfully
tested it with an Onkyo remote control (I think this one uses the standard RC5
protocol, but I'm not shure). Decoding happens on the computer; I use PC
Remote Control for this.
Okay, 'nuff said, here's the schematic (changed on July
08, 2002 to correct wrong connections to the MAX232). Obviously, it uses
Attention! It has come recently to my attention that
an SFH601, as shown in the schematic, is not the correct device for that circuit.
In fact, the SFH601 seems to be a 6-pin DIP optocoupler device and no IR receiver.
Unfortunately, all the devices which were sold to me as "SFH601 IR receivers/demodulators"
carry no markings, but I'm pretty confident now that my circuit contains the
SFH506 instead. The SFH506 isn't produced any more now, so the TSOP1736 is now
commonly used instead (the TSOP1836 is also said to work).
Please note that there are different types of MAX232s, which use different
values of external capacitors! Check first which type you've got before soldering
in the caps! Datasheets for these ICs are available at www.maxim-ic.com.
If the interface is positioned at a rather short distance to the host computer
(I guess a few meters are okay), a simplified version of the RS232 interface
may work. The simplfied interface uses a single transistor instead of the MAX232.
The resulting signal voltages are 0V and 5V, which are clearly outside the RS232
specifications, but are still correctly interpreted by modern RS232 receiver
circuits. The schematic for the simplfied version can downloaded here.
Please note that I have not yet built this circuit, so it's still untested.
The microcontroller firmware can be downloaded here: Firmware
V1.1. If you have questions, feel free to mail me at firstname.lastname@example.org.
I also have a (very simple) example
which shows how IR signal recognition can be done inside the mircocontroller.
- Klaus Stock
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