Holtek Decoder

[George]

I'm wondering if anyone has a subroutine to decode a Holtek chip - I've spent a couple of hours on it and am more confused now than when I started!!! I've done a search on here and found several people saying that a pic can easily take place of a holtek decoder chip - but in my brain - not so easy.

I have a LINX ready made transmitter with 8 buttons and a 10 bit address, from what I can figure out it does this:

sync bits: 01010
address bits (if set to 1111100000):11111111110101010101
data bits (button 6 pressed): 0101010101000101

a zero is represented as 00
a one is represented as 11
and open circuit (button not pressed or address switch open) as 01

where a 0 is a 380uS pulse and a 1 is a 760uS pulse, i was trying to do it with pulsin to determine pulsewidth and convert it, I was going to try and bring it in as serial data and play with it then - but it figured out to me to be 770bps - given that I'd get 20 data pulses (for the address) in 26ms and PBP doesn't allow that as a valid speed.

The encoding chip is a holtek HT640 (apparently it's the same protocol as motorola use)

Any help would be greatly appreciated - cheers

[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