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A Multifunction 330 MHz Remote
Control With an
ATTINY2313 Simulating the PT2264 Encoder
This 330 MHz remote control sends
sequences of control pulses to accomplish complicated tasks.
You can probably tell that I used
a lot of solder flux on this board.
Lots of flux not only helps the
solder wet to the copper, but it also greatly reduces solder bridges.
This project includes a low power radio transmitter. It is up to the
potential builder to determine whether the building and use of this
allowed by the laws governing the locality in which it would be built
Download the AVRStudio assembly source for
the program: pt2264i081004A.asm
Download the AVRStudio hex file: pt2264i081004A.hex
Download FreePC files in zipped format: pt2264 7th freepcb
Find updates at http://www.projects.cappels.org
I recently had an opportunity to make a RF remote control transmitter
to replace one that came on a commerical product. The commerical
product had only one button, and for many operations, the user was
required to send multiple timed code bursts by pressing that one
button. I figured that this was just crying out for a microcontroller.
And that is how this project got started.
This project is meant to be food for thought, or the starting point for
another remote control project, possibly involving a Princeton
Technology decoder. The actual firmware is customized for the
electronics in my motor control electronics and my ideas of how to use
it. in my own particular situation.
The Encoder And Copying The Functionality
I decided to see if I could make the
transmitter and simulate the Princeton technology chip used in the
key fob that was part of the commerical package, using an AVR
controller. I made a little RF diode detector and looked at the pulses
transmitted -not particularly fast, and that was encouraging. Then I
the key fob and found that the fob uses the PT2264 encoder, and
downloaded the data sheet. Connecting a scope directly to the code
output pin on
PT2264, and found the shortest timing period. After consulting the
data sheet I figured out that the clock frequency must be 13.25
Assembly Language Code
Armed with the clock frequency, I measured the resistance from each of
the address pins on the PT2264 to ground and V+, and from that derived
the code. The PT2264 address and data inputs have three logic states:
High (near V+), Low (near ground), and floating. After that it was a
simple matter of getting the timer in an ATTINY2313 to generate
interrupts at the an interval that is equal to the minimum interval
between transitions, then writing subroutines to generate the "High",
"Low" and "Floating" code patterns, and one more for the "Sync"
character, and then another to string them together to make the coded
control signal. Additonal routines proivded time delays.
The PT2264 address shown in the assembly language source file is one
that I invented for illustrative purposes, and is not the PT2264
address for particular installation for which I wrote it..
The ATTINY2313 comes in both surface mount and DIP versions, so I
breadboarded with the DIP because I could use a socket and with it, a Lazy ISP Socket
so I didn't have to put the ISP socket on the PCB.
Once the code as what I wanted, I switched to the surface mount version
of the ATTINY2313.
I had thought about switching to an ATTINY13 but
when I realized how the pin change interrupt, which is available on the
ATTIN2313 but not on the ATINY13, I dropped that idea. At 3 cm wide x 5
cm tall, the circuit board is small enough, especially if you consider
the enclosure I wound up with (shown elsewhere on this page).
Here is the structure of the program:
Start with power-on or when coming out of sleep.
registers and I/O, then
If any input pin is
the routine associated
with the first low pin tested.
Go to sleep.
else (if no pin is
Go to sleep.
The routines are as follows:
: Turn on the transmitter
and keep it on until power is removed or the reset pin is pulled low.
: Send the code
sequence once, just as when pressing the button on the key fob.
: Open the gate
so the motorbike can leave, wait a while, then close the gate.
: Open the gate
about one meter so the motorbike can enter, wait a while, then close
: Open the gate
about one meter so a pedestrian can pass through.
: Close the
gate after a pedestrian has passed through.
One feature of the structure above, is that all registers and I/O are
initialized each time the controller comes out of sleep, thus
refreshing the machine's state every time.
make a transmitter
The transmitter does not have to
be made on an etched printed circuit board, using a pattern on copper
clad board for the inductor/antenna results in more stable and
predictable operation than would a loop of wire. so I prefer it. The
inductors in the
earliest transmitters, such as the breadboard shown above, were cut
into a piece of copper clad board using a 1.0 mm drill bit in a
hand-held drill as a router. Crude, but it worked. This particular
setup used an AT90S2313 rather than a Tiny because I had not yet
decided which controller to use, and I still have a pile of AT90S2313's
to use up.
Once it looked like I could freeze the basic PT2264 address stream - I
really able to verify the actual code on the oscilloscope -I hooked it
to the oscillator in the photograph above and adjusted the pot. Imagine
the excitement, when I looked up and saw the gate opening! This was the
best confirmation that the PT2264 data stream was correct.
I tried a couple of different oscillator circuits and finally settled
on this one because it seemed better in both
terms of reliable starting with various components and the ease of
At first, I set out to make a transmitter that would operate from 12
volts, the same as the key fob. Once I got to the micro controller
I found myself making a 3 volt power supply, powered from the 12
supply, that would turn itself off at the end of a transmission. Well,
that seemed to be pretty silly when I realized that I was using a micro
controller that has a pin change
interrupt and can draw mere tens of nano amps when sleeping. That
to a 3 volt transmitter so I could dispense with all that power
The transmitter is shown in the partial schematic above. As mentioned
it is a Hartley oscillator. The inductor was made with a 0.09" trace on
The transistor is a KST10 in an SOT-23 package, from
Fairchild. This transistor was a nice choice because it also comes in a
package as the KSP-10.
Here are the important parameters to keep in mind if making a
Ft > 650 MHz when the collector current is 4
= 0.7 pf
The low 0.7 pf output
capacitance is very nice. The low collector-to-base capacitance means
oscillation frequency will have less dependence on battery voltage than
it would with a transistor with a higher output capacitance.
You might want to experiment with values R1, R3, or R2 to optimize the
bias for the particular type of transistor you end up using.
The 8 uH choke is a small ferrite bead with the wire passing through
the hole four times. I bought a whole bunch of them from what was
basically a walkie-talkie repair shop in Bangkok that had gone out of
the repair business, and I was anxious to find a use for this inductor.
In experiments after this one was made, I found that some chip
inductors I had come across, and measured 5 uH, worked just fine too. I
have some low-cost doorbell transmitters that operate at 315 MHz use a
plastic molded choke, so I am starting to think that the choke itself
is not very critical.
With only C1 connected directly across the inductor, setting of the
oscillator frequency was very critical. Adding a 10 pf capacitor in
series with the C1 reduced the tuning range and made tuning much
easier. I don't know what the specified range of C1 is as I bought it
surplus, but I measured the range to be 2 pf to 27 pf.
Once the transmitter circuit was working well, all that was left was to
add an ATTINY2313, a battery, and some buttons. The Princeton
Technology decoders, such as the PT2272, have an amazing tolerance for
data rates - about plus or minus 50%. The ATTINY213 is clocked by its
internal RC oscillator, and given the wide tolerance of the decoder, I
didn't bother to calibrate the oscillator. The five input pins are
configured as inputs with internal pullup resistors and the pin change
interrupt, set to interrupt when the pin makes a high to low
transition, is enabled for each input.
I'm not sure this is a really good idea, but instead of using a
the micro controller's power and ground pins, the controller shares the
pf decoupling capacitor with the transmitter. Maybe a larger capacitor
in parallel is a good idea.
Circuit Board Design
The entire circuit was laid out using a free program called FreePCB (www.freepcb.com
). As you may guess,
I chose this because its free. And I could layout the board without
using a schematic drawing program. There is a free schematic drawing
program, which is recommended on the FreePCB site, but for now, I still
like the looks of my old fashioned schematics.
The FreePCB design file, including the Gerber files, and a library with
the nonstandard components in available as a zip file, near the top of
I etched a printed circuit board using the laser toner resist method.
The smallest features are lines 0.025 inches wide. All parts were
mounted on the surface of the printed circuit board. Even the
through-hole style trimmer capacitor. I just bent the leads out into an
"L" shape and clipped them short.
U1 is mislabeled on the silk-screen drawing (above) as P2. H1 and H2
are the rows of pads used to connect the in-circuit serial programmer,
the battery, and the buttons. I have to point out that I did not
test this exact PCB layout. In particular, C5 was added to the layout
after I built this board. As with everything you find on the web,
proceed with caution and at your own risk.
In the hardware version shown in the photographs, C5 was added
after the board was etched, so the copper pattern above is not the same
as the one in the pictures. The transmitter I made after this one was
laid out using
the same L1, C1, and C5 pattern used in the artwork above, and it works
The board was laid out with spacing for 1206 components, except for R1,
R3, and C5, which are spaced for 0805.
The png files of the artwork are, according to the documentation for
PCB-Tools (the package that converted the Gerber files to png files)
generated at 200 pixels per inch, as, I think, is the gif image above.
In any case, you will probably need to adjust the scaling of the image
when you print it. Just make sure the pads for the ATTINY2313 have the
right spacing and everything else will take care of itself.
Soldering the #26 insulated wires to the tiny pads was not easy. Prior
to connecting these wires, I had connected wires from an Atmel
in-system programmer with which I programmed the chip. Those wires were
removed, a little more flux added to the pads, and the wires from the
battery and the button were connected.
The enclosure was purchased surplus. It has an integrated battery
holder for four AA cells, but when I tried to use it with just two AA
cells, for 3 volts total, the batteries would not stay in place. I
added a little bit of printed circuit board material hot glued into the
batter compartment solved the problem.
The top of the enclosure with the button labels temporarily held in
place with tape is shown above.
Since battery voltage has some affect on transmit frequency,
start with a fresh set of batteries.
The hard way;
with the transmitter a
distance from the receiver, and repeatedly push the "manual" button
while changing the setting of the tuning capacitor in excruciatingly
small increments. Once the transmitter is tuned, move further away
until the receiver no longer responds to the transmitter and retune.
Repeat until you get so far away that you can't get the receiver to
respond, then go back to where you were standing when the receiver last
worked, and retune. Very painful, and it does not give the best results.
The easy way:
I was overjoyed when I realised that my 60
MHz, 1 Gigasample per
second Tektronix TDS-2002 scope has some response up to the Nyquist
limit of 500 MHz. Good job, Tektronix! I used the scope as an FFT
analyzer, which gave me a spectrum analyzer display, adjusted the
scope's controls to put 330 MHz in the middle of the screen, with 5 MHz
per major division, and just tuned in the oscillator with C1. A
variation would be to use an
RF (no direct contact) UHF frequency meter or receiver with a signal
strength meter as a tuning reference.
Getting the transmitter tuned dead-on is very important,
especially since both the transmitter and receiver will drift a bit,
and the difference between transmit and receive frequencies affect
Contents ©2008 Richard Cappels All Rights Reserved. Find updates
First posted in October, 2008
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