16 (12) khz payphone controller. (Another prototype)

[dsk]

As the big spender I am,  I have invested in a frequency module, and redesigned my controller for the postpay/Spanish payphone.

It works, its, simple and easy to make. and affordable 

More details about the basic design are available here: http://tinyurl.com/ldbvv2t


dsk

[dsk]

  It died, I had not made good enough, incomming ringing killed the 16 khz module.
Have to make it better

dsk

[dsk]

While  I'm waiting for my new 16 kHz module, I have prepared to use this setup, Ill hope it works.
The reason for a common power negative and line wire is the typical 3 prong telephone jacks used here.

Please tell me if you have any ideas to make it better.

dsk

[unbeldi]

Have you tried one of these 16 kHz modules with one of those German time unit counters (Gebührenzähler), say by Siemens?  They were either built into an enlarged W48, or came in a separate box about 2" x 2" x 4" in size and had a reset key on the side. The central office supplied a 16 kHz pulse for each billing unit and the device simply counted them.

[dsk]

I have one grey plastic box with counter for 16 kHz, it is not 100% OK, It needs external power, but yes it works on this pulse. It is the same system.

dsk

one like this:

http://media35f.dimu.no/media/decoimage/TELE/TELE.Ch-105/35571?size=800

[dsk]

  Still testing, and it is not stable, sometimes OK sometimes not. And the line relay are not handling the current.
Back to the design department (desk).  I guess I'll go for a solid state relay to sense on the line. Constant power on the tone generator, and just switching the 16 kHz in and out.  Maybe an external box are better than putting it inside the phone, and maybe a (ADSL)filter to not feed the 16 kHz back to the exchange or ATA.

All more or less good ideas are welcome!

dsk

[Kimball321]

Why not use an ata that already sends meter pulses for pay phones such as

http://www.teldat.fr/fr/elmeg-T240-399.html

Taiwan Vector ATA, VT488 (not a link simply product I read about here) http://www.voip-info.org/wiki/view/Analog+Telephone+Adapters

[dsk]

Thank you! seems interesting. Do you know if the rate plan are programable in the ATA, or has to be signals from the exchange?

dsk

[unbeldi]

Why not use an ata that already sends meter pulses for pay phones such as

http://www.teldat.fr/fr/elmeg-T240-399.html

Taiwan Vector ATA, VT488 (not a link simply product I read about here) http://www.voip-info.org/wiki/view/Analog+Telephone+Adapters

I had to download the actual manual for the T240 to confirm that the charge pulse was actually 12 or 16 kHz, not just Hz as the web site claims. In any case, the unit however does not seem to support dial pulse telephones, so they appear rather expensive for just providing a 16kHz pulse.


Didn't Elmeg at first simply resell Snom SIP and H323 phones?

[unbeldi]

Some posts in the German antique telephone forum at wasser.de discuss generating 16 kHz pulses and they suggest to use a model 55 (T) unit counter in reverse to feed the 16 kHz signal into the local loop for the telephone or pay phone to digest. I think they are disconnecting the mechanical counter internally and feed the signal in reverse into the unit at those points.  I presume this takes care of filtering any ringing voltage through the internal network, consisting of signal transformers, inductors, and capacitors.

In any case, if you're using your own signal generator for the 16 kHz tone you need some protection indeed for your circuit. Central will never send ringing and a timing signal at the same time, so there is no problem, and they don't send ringing while a phone is making a call.

The ideal position to place the signal generator is as close as possible to the exchange, such as an Asterisk system. With that it is conceivable to activate the signal generator directly in software with a relay AFTER a call has been set up.

[dsk]

Not easy  I killed my first signal generator on an incoming ring  and the relay are a little quick so it acts on ringer current.
I guess that's solved, now the stable 16 kHz are the problem.

http://imgs.inkfrog.com/pix/smoothdealer/27361-B2.jpg

dsk

[dsk]

After months of testing, I have not touched the tuning knobs since December, and it works, but it needs up to 48 hours to be stable after a power out or disconnection from the mains.  I guess it is possible to find a more stable 16 kHz source for a few more $$, but this are just for fun, and it has not been a big problem.

dsk