In the September 2004 issue, we showed you how to assemble
"Rudolph the Red-Nosed Reindeer". Rudolph is a simple Christmas
decoration with flashing LEDs that can play a variety of tunes,
including mobile phone ring tones. As promised, this month we
assemble the infrared remote transmitter and add the receiver
components to Rudolph’s PC board.
Before we describe how to assemble the various pieces, let’s
first take a look at the basics of infrared transmission on the new
Infrared remote control
The PICAXE-08M includes two commands for sending and receiving
data over an infrared link. The infraout command sends data
on pin 7, whereas the infrain2 command receives data on pin
3. Data is transferred using a simple modulation technique based on
the well-documented Sony Infrared Remote Control System (SIRCS)
Fig.1: basics of the SIRCS protocol, showing
the composition of each serial transmission. A logic "1" is
represented by a 1.2ms burst of the 38kHz carrier, whereas a logic
"0" is represented by a shorter 0.6ms burst. Each bit is separated
by a gap of 0.6ms.
The SIRCS protocol uses a 38kHz modulated infrared signal
consisting of a start bit (2.4ms) followed by 12 data bits (7 data
bits and 5 device ID bits). Logic level "1" is transmitted as a 1.2
ms pulse, logic ‘0’ as a 0.6ms pulse. Each bit is separated by a
0.6ms gap (see Fig.1).
When used within Sony production devices, the 5 device ID bits
represent the type of equipment (1 = TV, 2 = video, 26 = DVD, etc).
The 7 data bits represent different commands (1 = channel 2, 2 =
channel 3, 16 = channel up, 20 = mute, etc). Within this PICAXE
project the Sony-allocated commands are not relevant, but a full
list is provided in the PICAXE manual for those interested in
controlling their own Sony hardware!
To transmit infrared data, the PICAXE command is:
For example, to send the Sony command "TV - mute", the command
would be infraout 1,20. Note that device should
always be 1 when used in PICAXE projects and data can only be
between 0 and 127, as the SIRCS protocol only specifies 7-bit
The full program for the transmitter is shown in Fig.6. As
infrared signals are easily corrupted, the data is actually sent 10
times to increase reliability. This matches commercial remote
controls that tend to transmit the data at 45ms intervals whilst the
button is held down.
Note that the program uses codes "1", "2" and "3" for the three
switches, but you can edit these to any number between 0 and 127.
This would be useful when you want to control multiple units in the
same room, using different data commands for each unit.
Building the transmitter
As hinted at in September, the various tunes played by Rudolph
can be triggered remotely using an infrared transmitter. This simple
project uses a PICAXE-08M micro, three push-button switches and an
infrared LED to make a complete hand-held remote, the circuit for
which appears in Fig.2. A second visible LED is included for user
Fig.2: circuit diagram for the simple infrared
transmitter. As no serial link socket is provided, the PICAXE chip
must first be plugged into the "Rudolph" PC board (described in
September 2004) for programming.
Assembly is very straightforward and should only take a few
minutes. Begin by installing a wire link in the position indicated
by a dotted line on the overlay diagram (Fig.3). An off-cut resistor
leg is ideal for the job. Note that as an IC socket will be mounted
over the link, it must be lying flat on the PC board before
Install all of the resistors, switches and IC socket next, making
sure that you have the notched (pin 1) end of the socket around the
Install the two LEDs next, noting that the infrared LED (IRLED1)
leads must be bent at 90 degrees so that it points away from the PC
board (see photo). Make sure that you have the flat (cathode) sides
of the LEDs oriented correctly. The infrared LED may be supplied in
either a "black" or "water clear" epoxy package.
Finally, solder the battery leads to the positions indicated
after threading through the adjacent hole. Note that the board runs
from a 4.5V (3 x AA) battery pack – do not connect a 9V PP3
To reduce overall size, a serial link socket is not provided on
the transmitter PC board. Therefore, the PICAXE-08M chip must be
programmed on the main Rudolph PC board and then transferred to the
Fig.3: the overlay diagram for the infrared
remote transmitter. Install the wire link (under IC1) first, then
all the other parts, making sure that the IC socket is around the
After assembly and programming, you can check transmitter
operation by looking at the infrared LED "end-on" through a webcam
or digital camera (such as a mobile phone camera). Although the LED
is not visible to the naked eye, these camera are sensitive to
infrared light and so the infrared LED will display a faint glow on
the camera screen whilst operating.
Fig 6: Transmitter Program Listing
' Wait until switch press
if pin1 = 1 then
if pin2 = 1 then tx_2
if pin3 = 1 then tx_3
let b1 = 1 - 'Code 1
let b1 = 2 - 'Code 2
let b1 = 3 'Code 3
' Transmit code 10 times for increased reliability
Legs Versus Pins
high 4 - 'visual LED on for user feedback
b2 = 1 to 10 - 'send infrared code 10 times
low 4 'LED off
In PICAXE BASIC, "pin" refers to a logical input or output
port number, not a physical pin. Conversley, physical pins are
referred to in the PICAXE documentation as "legs". Confused?
We’re not surprised.
When describing a PICAXE circuit, SILICON CHIP will
continue to refer to physical pins as "pins", just as we do
for all our projects. We’ll leave the legs for the organic
Extending transmitter range
A 330Ω resistor is used in series with the infrared LED to limit
current flow from the PICAXE port pin to an acceptable level. This
gives a transmission range of about 4-5 metres, which should be
enough for most users.
Fig.4: transmission range can be increased by
adding an external transistor circuit to drive the infrared
However, infrared LEDs can typically be driven with a much higher
current, thus extending the potential transmission range. If you
need the maximum possible range, then a transistor driver circuit
can be added between the PICAXE infrared output pin and the LED, as
shown in Fig.4.
The infrared receiver portion of the "Rudolph" circuit from last
month is reproduced in Fig.5. Any PICAXE-08M project can receive
infrared remote control signals with the additional of these four
A Vishay TSOP4838 infrared receiver IC demodulates the 38kHz
carrier wave to give a logic output. It also contains filters to
suppress noise signals from devices such as fluorescent lights. The
block diagram of the receiver is shown in Fig.8.
To receive infrared data, the PICAXE command is simply:
This command waits for a valid input signal and then stores the
data in a variable named "infra". This variable can then be used to
play different tunes, as shown in the full receiver program in
Fig.5: any PICAXE-08M can receive infrared
remote control signals with the addition of just a few components,
as shown here.
As the PICAXE-08M uses the standard SIRCS protocol, the receiver
will also work with commercial "universal" style infrared remote
transmitters. These are widely sold as "one-for-all" replacements
for use with home audio and video equipment. All you need to do is
program them with one of the Sony-compatible equipment codes from
the supplied list of manufacturers codes.
Fig 7: Receiver Program Listing
' ***** main loop *****
infrain2 - 'wait until
'debug infra - 'optional display on screen
' ***** play tune *****
'play tune depending on light
if infra = 3 then play_xmas
if infra = 2 then
if infra = 1 then play_jingle
play_jingle - 'internal tune Jingle Bells
play_silent - 'internal tune Silent Night
play_rudolf - 'internal tune Rudolf The Red Nosed Reindeer
play_xmas - 'external ring tone tune
'We Wish You a Merry Xmas
Only two parts remain to be added to the Rudolph PC board. The
receiver IC is soldered into the "IR" position, with the leads bent
over so that it lies flat on the board.
A 4.7µF capacitor is also added to filter the supply, noting that
the positive lead goes in as indicated by the "+" marking on the
overlay diagram. The 330Ω and 4.7kΩ resistors should already be
installed on the board, as they were part of the original
Finally, reprogram Rudolph with the BASIC code listed in Fig.7,
which adds the necessary infrared remote control functions. That
done, you should be able to choose between three tunes using the
buttons on your remote control board!
With a minimum of external components and the new infraout
and infrain2 commands, you can add remote control capability
to all of your PICAXE-08M projects. "Rudolph the Red-Nosed Reindeer"
demonstrates how it all works, and might even be a party favourite
Fig.8: this diagram reveals the basic
functional blocks within the TSOP4838 infrared receiver. As well as
the actual PIN (photo) diode, it includes amplifier, discrimination
and demodulation circuits to reconstruct the original digital data,
which appears on the "OUT" pin.
1 infrared PC board
3 miniature pushbutton switches (S1 - S3)
1 battery clip
1 3 x AA battery holder
1 8-pin IC socket
1 PICAXE-08M (IC1)
1 Vishay TSOP4838 infrared receiver IC
1 5mm yellow LED (LED)
1 5mm infrared LED (IRLED)
1 4.7µF 16V PC electrolytic
Resistors (0.25W 5%)
Also required (not in the kit)
Rudolph kit (part no. AXE107S)
PICAXE Programming Editor software (v4.1.0 or later)
PICAXE download cable (part no. AXE026)
3 x AA alkaline cells
Obtaining kits & software
The design copyright for this project is owned by
Revolution Education Ltd. Complete kits (Part No. AXE108S)
and/or the Vishay infrared receiver (Part No. LED020) for this
project are available from authorised PICAXE distributors –
or phone Microzed on (02) 6772 2777.
The PICAXE Programming Editor software can be downloaded
free of charge from http://www.picaxe.co.uk/
or ordered on CD (part no.