[VoIP] Asterisk and Payphones

[Lee Spenadel]

Mark,

My BSP for the 1D/2D Coin Telephone Set shows:

Operate Current: 41 mA
Non-Operate Current 30 mA
Operate Time of 450  +/- 50 ms

Lee

-----Original Message-----
From: voip-bounces at ckts.info [mailto:voip-bounces at ckts.info] On Behalf Of
Mark Rudholm
Sent: Tuesday, July 31, 2007 1:16 AM
To: Voice Over IP Tandem for Analog Switches
Subject: Re: [VoIP] Asterisk and Payphones

Well, I'm glad to hear there is significant interest in this.

For the moment, I'm working on coin-relay control.  My first
draft of the schematic is available here:
http://rudholm.com/coin-control.pdf (use "File, Rotate" to
fix the orientation in Acrobat Reader).

My idea is just to take two TTL lines from the computer, either
from the parallel port or from a USB to parallel adapter
(like the Elexol USBMOD4), one for return vs. collect and
the other as a strobe to trigger the relay.  If I use the
parallel port, I'll need to add a +5VDC power supply to my
interface box to power a TTL buffer since parallel ports
can't source or sink enough current to safely drive those
solid-state relays.  The Elexol interfaces can source enough
current to operate them however, and also since USB ports
have a nice 500mA +5VDC supply line, I could throw in a
buffer as well.

I'll build the circuit described in that schematic on a
proto board as soon as my Mouser order for the parts arrives.
Once I get it working right and get the relay timing right,
then I'll start thinking about the TTL control lines.

Speaking of which, if someone could look up in their Coin
Crafts or Coin Services Manual Volume I what the coin relay
timing is, I need that information.  I'm guessing it's
about 500ms but would like verification.

Once the hardware is done, it shouldn't be too hard to
do a simple return or collect from Asterisk based on whether
the call supervised or not.

Mark Spencer pointed out to me that DTMF detection is
actually not done in zaptel but in a simple goertzel analysis
in dsp.c, which makes sense for DTMF decoding.  He suggested
I just add a new column and row for 1700 and 2200Hz coin
tone.  I figure I'll start hacking the code once I get the
hardware working.  I would ultimately like to be able to
fully emulate ACTS.

I would eventually like to add the Stuck Coin, Coin
Presence, and initial rate deposit tests to the system.

Support for coin first phones would be nice, but I need
to get my hands on the Coin Services Manual to even start
thinking about how I'd support all these functions.

Three-slot support would be interesting.  I understand the
coin bells are tuned so it shouldn't be too hard to
add the two tones to the goertzel analysis (one for the
nickel/dime bell, and one for the quarter gong).

My ultimate goal would be to publish a patch set for the
relevant files in asterisk and a schematic and Mouser
part number list.  The circuit is too simple to really
justify custom printed circuit board artwork (it someone
wanted to do that, that'd be fine with me, though).

-Mark

Greg Blakely wrote:
> I don't know if you'd be able to include a 3-slot patch in the project,
but
> my payphone is a pre-pay 3-slot Automatic Electric.  It has the "ding"
bell
> for nickels and dimes, but using a "gong" for a quarter. 
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