Looking for some HOLTEK DTMF dialler chips.

[David Chapman]

I need a quantity (up to 100 pieces) of a Holtek DTMF dialler chip but
their UK distributor has just informed me that they have now ceased
production of all dedicated dialler chips.

Before considering approaching any of the various (rather dubious and
mainly Far-Eastern) parts-finder services being offered on-line I
thought I'd ask in this NG just in case anyone has any surplus stock of
either of the following devices:-

HT9305A-18DIP or the rather older HT9315A-18DIP

Alternatively, can anyone recommend a trustworthy parts-finder
company, preferably in the UK, that may be worth contacting.

TIA - Dave.

 

[Jamie]

I need a quantity (up to 100 pieces) of a Holtek DTMF dialler chip but
their UK distributor has just informed me that they have now ceased
production of all dedicated dialler chips.

Before considering approaching any of the various (rather dubious and
mainly Far-Eastern) parts-finder services being offered on-line I
thought I'd ask in this NG just in case anyone has any surplus stock of
either of the following devices:-

HT9305A-18DIP or the rather older HT9315A-18DIP

Alternatively, can anyone recommend a trustworthy parts-finder
company, preferably in the UK, that may be worth contacting.

TIA - Dave.

I can't offer you a source but I can offer you a alternative method
that may work, at least it did for me to replace a chip in a radio for
a automatic keyer.

I found a family of PIC chip that was pin for pin compatible with the
original chip as far as the rail legs and IO were concerned. Who knows,
maybe that is what it was in the first place? But I was able to program
that chip to produce the exact results of the original with a little
enhancement to it..

You may want to look that way if your search for replacements come to
a dead end.

Jamie

 

[hamilton]

I found a family of PIC chip that was pin for pin compatible with the
original chip as far as the rail legs and IO were concerned.

Which PIC has the VSS/VDD on pins 9/10 of an 18-pin dip ??

 

[Nico Coesel]

That chip probably has some analog to it -- but an 18-pin DIP-sized PC
board might give you enough room for a PIC and an op-amp circuit.

That won't be necessary. IIRC I once quoted a circuit like that based
on a cheap & small MSP430 device. PWM and an RC filter should do the
trick.

 

[miso]

I'm not familiar with that chip, but generally there is more to a dialer
than just producing DTMF. You need to do call progress detection. It
varies from country to country, but basically you need to determine if
there is a dial tone first. Once you have a dial tone, you blurt out the
digits then listen to the line. There still may be a dial tone (i.e.
fubar), or you have ring detect or a busy signal.

You could still do it with a PIC, but it is slightly more complicated
than you think. But probably not much more complicated. In the dark ages
of split band modems, you would take one of the band separation SCFs and
change the clock so it overlapped the dial tone frequencies. Using an
energy detection circuit, you would decide if a dial tone is present.

I've designed the circuitry in the dark ages for modem CPD, but there
are still chips that do just that function. [I can't claim first hand
use of these chip. This is just the first valid good hit.]