Holtek Decoder

[mackrackit]

This might help
http://www.holtek.com.tw/english/tec...df/ha0040e.pdf

Or this
http://www.picbasic.co.uk/forum/showthread.php?t=6436

With the help I received from the above thread, PIC to PIC and no wires!! Also has more capability as it is not limited to 8 or 10 signals.

If you want, I can post the good code when I get back to the shop(can not do it from memory)

[George]

I've done pic to pic with no wires - I'm wanting holtek to pic with no wires - the remote I've bought has a holtek chip in it so need to decode that - do you have code for a holtek? If so I'd love to see it

Cheers

[dhouston]

There are far, far too many variables.

There are several different Holtek chips and the chip frequency (and thus the pulse/space duration) depends on the value of the resistor used for the oscillator. Some use a two state code, others use a three state code. You need to study the Holtek datasheets for the specific encoder and decoder chips you are using.

Does wireless mean IR or RF? If RF, ASK or FSK?

[mackrackit]

I've done pic to pic with no wires - I'm wanting holtek to pic with no wires - the remote I've bought has a holtek chip in it so need to decode that - do you have code for a holtek? If so I'd love to see it

Cheers

Sorry, no code for the holteks.

In your case just buy the correct decoder.

[dhouston]

I've attached a GIF showing the output waveform from the HT640 sending all ONES, all ZEROS, all ELSE, and repeating those three in ONE, ZERO, ELSE order.

First, you have to pick the start sequence out of the air (usually signals are sent 3-5 times with the first few setting the receiver AGC) and then capture and decipher the following bitstream. You might do this using the CCP hardware in Capture mode, resetting the polarity after each interrupt but it's not a simple task.

As you can see there are two different pulse widths and two different space widths. The actual widths will depend on the transmitter oscillator frequency.

The best advice is to use the Holtek decoder chip with the same oscillator frequency as used by the transmitter.

[Bruce]

The attached code example will decode the Holtek HT640.

Download the Linx .PDF below for details of the 640 data
structure.

http://www.linxtechnologies.com/Docu...datastruct.pdf

[George]

Hey thanks Bruce exactly what I was looking for

[Bruce]

Hey George,

You're most welcome. It's pretty old, but it's simple & it works.

You can improve the synch bit check part by replacing it with this;

IF PBIT[0] <= PBIT[1] THEN Begin
IF PBIT[1] >= PBIT[2] THEN Begin
IF PBIT[2] <= PBIT[3] THEN Begin

And you can remove this part; IF Loops > 2 THEN Begin

I stripped a lot of code out before posting it, but missed that line. It's bits &
peices of a much larger program that was a first go at decoding the Linx
hand-held.

[tekart]

Bruce,
Just wanted to thank you for posting that Holtek Decoder code. Really nice job and extremely well documented. I had a job up and running using the Linx CMD-KEY keyfob transmitter in minutes thanks to you. Much appreciated.
Guy

The attached code example will decode the Holtek HT640.

Download the Linx .PDF below for details of the 640 data
structure.

http://www.linxtechnologies.com/Docu...datastruct.pdf

[Bruce]

Hi Guy,

You're very welcome, and thank you too. I'm glad you found a good use for it.

Edit: If you ever need to create your own PIC chip to emulate the Holtek 8-bit encoder too, I posted a pretty cool project for the Crownhill Amicus board here http://www.myamicus.co.uk/content.ph...Remote-Control with code for one.

And PC software to control the PIC, so you have a PC-based encoder to control your PIC-based decoder. Pretty fun stuff...