Mark Zenier wrote in message
...
In article , N_Cook wrote:
Like breaking a combination lock you need a "tell " to work on.
Assuming a piece of kit, impossible to get a remote control for and
"universal " remotes do not register any change to the otherwise dead
kit.
If you broke into a ground or supply line to the microcontroller and
monitored the supply current , would there be staged changes of current
when
exercised by various , but vast majority wrong, IR signals?
ie simple swept 30 to 50 KHz oscillator source would you pick up on say
38KHz as the basic required "carrier" frequency ?
Varying mark/space of gated pulses at that "carrier" f, would you pick up
on
the correct mark/space
?
On the receiver side, the IR detector module (or optical IC) contains the
AM tuned receiver and outputs the demodulated baseband digital signal.
All the microcontroller will see is the coding, not the carrier.
With about a 1 kHz bandwidth. It's ttl or open collector digital output.
The modules come fixed tuned for a large number of frequencies, from about
20 kHz to 100 kHz. Sharp made a lot of the modules. I think Infineon
made the IC versions. You could point a modulated LED at the reciever
module and find the carrier frequency by sweeping the LED drive frequency
and looking at the module output.
Then would there be a recognisable respone to various random "nibbles"
that
are parts of the required coding ?
Each message usually has all sorts of error detecting or correcting bits.
Often in the form of repeating the data, inverted. Or checksums or
crcs, stuff designed to prevent false operations. With about 10 to 30
bits per message, finding it by random would be too much to hope for.
In the old days with dedicated chipsets, you could read the datasheet,
but now the transmitter could be a cheap micro.
Different manufacturers had standard multifunction message protocols.
Elektor published a number of the different message formats, (Philips
and Sony, I think). But for odd gear, only the software guys who wrote
the firmware would know.
Back in the first few issues, back in the late 1980's, Circuit Cellar
Ink magazine had a project for a universal recording remote control.
But you would need a working remote for that.
Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)
There is one design aspect in out favour. To have many buttons/functions on
a zapper and not destroy ease/speed of use, the designer cannot add
repeats/checks & long code/decode sequences willy-nilly, as no one will put
up with a button-press response time of seconds for consumer use
Another thing I may get around to trying with this "universal"
http://www.amazon.co.uk/
7dayshop-Universal-Control-Learning-Function/dp/B0043VTRAQ
is it uses a simple 6MHz ceramic resonator. Replace with sig gen and vary
the timings in search mose. I've done this before with another remote.
I have another one-time target machine a PVR that I could not crack the
coding of but managed
to get a replacement zapper for. If I can find a way of cracking that one
withoutout recourse to hindsight knowledge from reading the bought one, I
may (unlikely I know) be getting nearer a true universal system