Electronics

George · Guest

Hi,

I've considered building my father a dedicated remote switch which
could mimic the "mute" code for his TV remote. The TV is a Mitsubishi
VS-5017S (one of those older, giant ones).

I've read through a bunch of the remote related posts here and have
gone through some web info, which was mostly for repeat/extenders and
some relay trigger circuits, etc.

For the command code itself, I've seen some sites on how to obtain a
remote's signals, and they looked fairly straightforward, but I'd
obviously rather find the info online to save some time, if it's
already been recorded by someone else.

Assuming I can find out what to send for "mute", does this transmitter
endeavor sound overly difficult or impossible for someone on the
novice level? If not, could anyone possibly point me to a decent DIY
example or some info somewhere on how to go about it?

It would probably only be worthwhile if the device were relatively
compact and could be supplied by a small internal battery. I've got
some PCB layout/etching capability here, and If there might be a
microprocessor involved, I've done some simple PIC programming, which
required a few tedious clock cycle/timing adjustments for proper
serial rate output, so that would probably be the better "brain of
choice" for me. Don't know how complicated a circuit or application I
would be able to handle though.

Much Thanks!
(and please reply within the group)
George

Ken Taylor · Guest

"George" <george@nomail.com> wrote in message
news:qjedp1t1hb3cbuh7qjdjj20nulack91quc@4ax.com...

Guest

I've done a fair bit with IR using PICs. I've used a 12F683 to drive a
transistor which in turn turns on and off an IR LED.

The 12F683 has a HPWM module, this means you can turn on and off the
modulated signal very easily. All you need to do is program a few
registers with values that result in the correct modulation and duty
cycle for the signal you're sending. This PIC also has an internal
clock so there is no need to worry about external crystals etc.

The software then needs to turn the HPWM output on and off with the
data signal its trying to send, and you have a modulated signal going
straight to the IR circuit.

The HPWM output pin needs to be connected to the base of the
transistor. The IR LED, resistor and transistor (collector/emitter)
connected in series to complete the signal circuit. The reason for
driving it from a transistor is that the IRLEDs draw more than the 25mA
that PICs allow. I've used a BC549, but there are probably better
parts around as the BC549 has a maximum of 100mA while the TSAL6400 (IR
LED) can easily draw 100mA. The resistor values needs to be calculated
based on the supply voltage and the rating of the IR LED you use.

I've run this type of circuit off a tiny battery for many many presses
and it works fine. My design caused the power circuit to complete when
a button was pressed so there was no need for standby/sleep modes on
the PIC. It took the form of a 3 button car remote style device, each
sent a different signal series. Combined with a TSOP4837 (I think)
receiver for learning new signals this proved a handy device for a lot
of people.

There are loads of articles on the net around IR signals, RC5 codes
etc, so you need to find out what signal type this TV uses. Also
remember that a lot signals are toggles, the only exception being power
which often has an on, off and toggle signal.. allowing more
flexibility in the way its used.

Components:

PIC 12F683 £1.30
TSAL6400 £0.25
BC549 £0.10

Glenn Gundlach · Guest

George wrote:

Spehro Pefhany · Guest

On Wed, 07 Dec 2005 03:02:05 -0800, the renowned George
<george@nomail.com> wrote:

Martin Riddle · Guest

The philips RC5 protocol has been hacked a long time ago. I have a 8051 based reciever, that worked well at the time. It is a
learning experiance, very little hardware.

Cheers

"George" <george@nomail.com> wrote in message news:58vep159l6o96csh7muv3nrpalbi56pt64@4ax.com...

George · Guest

Thanks guys!

I see a list on the LIRC site of nine 8bit Mitsubishi files-

http://lirc.sourceforge.net/remotes/mitsubishi/

I'm not sure if one of those models might accept the same series of
crap that this set wants, but I do notice the same hex value for mute
in a couple of the files. I also don't know if that info is
specifically formatted for the LIRC software, or if it contains all
the details I would need to create the mute signal with anything else.
I'll keep fishing and look back at those decoding sites/circuits to
see if it looks too hard, but maybe someone else can tell from
glancing at one of those text files if that's what I need. I've got a
regular 40MHz scope here, but no fancy "freeze frame" type, so I guess
I can only see timing info etc. (also have a separate freq. counter).

On 7 Dec 2005 "Glenn Gundlach" wrote:

Guest

The PIC that I used I selected because it has the builtin hardware PWM.
This allows you to generate many different output frequencies no
matter what speed you clock it at. It also has a reliable built-in
clock source so no need for external crystals or resonators.

The circuit is tiny (when on a PCB). For the project I used the
following case available from http://rswww.com - search for 451-0674 or
just the word Keyfob and you'll find it!

I didn't have any problems with power-up delays because the PIC has its
own power-on delay to ensure its stable so that wasn't a worry.
Powerdown was instant, just as on a remote. My circuit went something
like this:

+---------------+
| |
| PIC 12F683 |
| |
+---------------+
[ ] [ ] [ ]
| | |
| | ---
| | -
| |
| |
___ | ___ IR LED RED LED
+v ----o o----+---/ \----->|------->|----+
|
---
-

Sorry - first try at ASCII circuit diagrams! The red LED was used as a
confidence thing, and depending on the LEDs used depends on if you need
a resistor or not. The whole circuit works off a 3v cell (lithium).
The cases I've mentioned take a 12v cell unfortunately, so in that case
I used a very low powered 7805 to take it down to 5v which works well.
I did try and find a 3 to 5v cell in the same size, but couldn't find
one.

I typically clock my projects at 4Mhz unless I have a reason to need
the other frequencies. You use various registers to calculate out the
PWM frequency you need for the clock speed you're running at. So for
example, so you need a 38Khz modulation you'd take 4Mhz = 4000000,
divide by 4 = 1000000. Divide this number by the frequency you need,
38000, this gives you 26 (when rounded). Load this in to the PR1
register (I think). Obviously because of the rounding you'll be
generating a slight offset, you'll generate 38461Hz. Thats close
enough not to make any noticable difference to the range or sensitivty.
If you play around with the pre/post scalers on the time you might be
able to get something more accurate.

You'll also need to configure a duty cycle, I think most remotes are
about 20%. You need to work out the number of bits available for your
clock and duty cycle. Its in the datasheet... so work it out and from
there you look at the: I've got 6bit resolution (for example), the
lower two bits sit in one of the PWM register, the remaining upper 4
bits sit in their own register. Be sure to clear the upper bits of the
that register when you configure it, otherwise it can do odd things.
If we're looking at a 20% duty cycle at 6 bits you need to store the
decimal value 12. Zeros in the lower two bits, and the number 3 in the
upper byte. I hope all that makes sense, but unless I know the exact
frequencies I can't give you precise values.

Then only timing you need to work out is the one for the real signal,
which can be done in most high-level languages rather than worry about
asm. If you needed to do the whole modulation in software you'd need
to asm only otherwise the high level language will screw up your
timing.

Comm port serials i'd be careful of.... they don't typically use basic
IR they're normally Irda or something else....

If you want to work out what the IR signal is, the way I did it was to
buy a Vishay TSOPxxxx part. That has a logic output that you can
connect on to a PIC. Then all I did was have a timer routine, it
starts a timer, waits for a state-change on the pin, stores the timer
value at that point, clears it and restarts the timer, then sends the
result via the serial port (in ASCII). Run a terminal program at the
other end, this will dump a load of numbers out giving you the timings
for the signal received. Its how I reverse engineered a proprietry
system that didn't use standard codes. Obviously you have to repeat
the codes a few times to get reliable results but it should give you a
good idea of what to generate. As a test I just too the timer figures,
put them in a table, then altered the code to turn on and off the IR
output in line with the table and the timer - resulting in the signal I
needed.

I hope that makes sense! For the record I use Proton+ to write PIC
apps in... its a bit faster than using asm (which I have used for
things like the 68HC705C8 - old process now!)

Mike

George wrote:

Ian Stirling · Guest

George <george@nomail.com> wrote:

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