[time-nuts] IRIG-B audio decoder circuits and ICs sought

[Esa Heikkinen]

Joseph Gwinn kirjoitti:

>> I prefer the DC level shifted variant of IRIG-B.
> I like and use IRIG-B00x too, but it only reaches a few meters, versus 
> the required tens of meters.

It's differential RS485-alike bus (with TS2100 at least) using 5V 
signalling level. It works easily more than few meters with twisted pair 
cable. For RS485 they claim more than kilometer if the speed is less 
than 100 kbit/s and here it's only 100 bit/s. So only tens of meters 
there's no problem.

I think the AM was originally intended for transmitting IRIG-B 
wirelessly or analog tape/film soundtrack recoring...

> Yes, but I must have IRIG-B12x (Amplitude modulated 1 KHz sine wave), 
> and the analog processing complicates things.  I think that one best 
> implements the IRIG decoder in a DSP chip.

Yes and there will be delays. As long decoding delay remains constant, 
it's easy to compensate. In my implementation the decoding delay is 48 
cycles (9,6 usec) and remains constant. Actually this is delay from 
rising edge verification to timer setting point.

When decoding IRIG-B it's one second behind. Timekeeping functions are 
needed anyway. Data verification system comes as a side product. It's 
only needed to compare last received IRIG-B frame with timestamp of 
passed second. If times differ then there's bit errors OR timekeeping is 
out of sync. Code has to decide when it should just ignore the received 
data and when it should syncronize the internal timekeeping.

> TS2100s are generating a lot of replacement business for GPS vendors.

Yes, planning to buy at least one spare unit when their prices will drop 
on Ebay... :)

> To be modern, one must code in C?  Isn't that true?

I use assembler only with these 8-bit PIC's. It's little bit special 
case, there's no point to use assembler with any larger processors. This 
little baby has only 35 assembly commands. Because most of them run in 
single cycle it's quite easy to write time critical code like this 
IRIG-B decoder.

-- 
73s!
Esa
OH4KJU