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generate telephone ring

I have been given a task of creating an automated test for a Telephone Line Manager. Can LabVIEW be used to simulate a telephone ring to test the board. Is there a special toolkit for this or can it be done with just the developer suite? Any help is greatly appreciated.

 

Chirs

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You can certainly simulate a ring voltage with LabVIEW but since an actual telephone ring is somewhere between 50 and 90 volts (if my memory is correct), you would need some actual hardware to generate a real (not simulated) ring. Do a search for line simulators (i.e. Teltone) or build your own circuit.
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I think I was a little too generic in my question. Let's see if I can reword it. What I have been asked to do is convert an old "Frankenstein" automated tester over to National Instruments using LabVIEW. I guess the best thing I can ask is Does anyone know if there are any books on LabVIEW that go into Telephony testing. Meaning measuring Loop Current, DTMF Tones, Signal Paths, Ring Signal/Generation. The test now is very involved and I need to start somewhere. Any help is greatly appreciated.

 

Thanks

Chirs73

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That is a much better explanation of your project.

 

I think you need to separate your request into two parts: (1) What information is available on phone testing? and (2) What books about LabVIEW are available?

 

The answer to (2) can be found by searching the Forums.

 

Until you have specifications on your testing, it is premature to ask about how to do it in LabVIEW.

 

I have heard or read somewhere that at least one of the big cell phone manufacturers uses LV in its testing.

 

Do you have any documentation on your existing tester?  Particularly functional test specifications more than how it works.

 

Lynn 

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Thanks for the quick repsonse. As for documentation for the existing tester there really isn't much. I have the error code list and know a few things about this tester. The tester was here way before I was and is starting to show symptoms of failing. Which is why I need to create a test using LabVIEW if possible. The only measurement needed that concerns me is the ring voltage wich is somewhere between 50-90V AC. The other measurements can be done with what we already have (PCI-6221 and SCC-68)

 

Chirs73

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I don't know of any resources that discuss LabVIEW and telephony. I did this sort of thing for about 9 years until about a year and a half ago.

 

If you have a basic understanding of the technology, then the next step is to select test equipment that is capable of measuring or sourcing the signals. There is specialized equipment or you can start with some basic DAQ cards and add custom circuits to provide the correct loads and impedance matching. For example, any of the DAQ cards card be used to generate a DTMF tone. You just use two different sine functions, add the result, and pass it to a DAQ write. I don't know of any NI card that could generate a ring tone but it's certainly possible if you add some external circuitry. Measuring Loop Current is possible with any number of instruments, including a DAQ card if you don't have an instrument designed specifically for that. I used cards from GL Communication to generate T1 signals and analyze those and the cards also had some analog test capability. They have LabVIEW VIs available and an ActiveX interface. Once upon a time, we used an old PCM test instrument from HP but it was obsolete and expensive. We initially used two DAQ cards and a custom load board for all analog testing. This was capable of testing 24 channels simultaneously. Eventually, we designed our own card that had a USB interface.

 

As I said, I think I would approach it from a hardware viewpoint. There is very little hardware that LabVIEW cannot control.

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Hi Chris, this measurement can be pretty easily taken using your PCI - 6221.  The only hurdle will be to drop the voltage down to a level that wont destroy the card.  You can do this using a high resistance (10k - 100k) voltage divider circuit.  Use resistors with no more than 1% variance in reported resistance value.  Drop that 50-90 volts to 5-9 volts and you will have no problems.  (if these values are RMS voltage and not peak, you will have to drop the voltage down further until peak voltage is within -10 to 10 volts).

 

Once you do that, aquire a waveform of your ring tone at about 10x the maximum frequency in the ringtone (or the 6221 max sample rate, whichever is lower).  Take readings for as long as you need them.  Then just use a power spectrum or RMS voltage VI to analyze the waveform.  This can accctually be done entirely with express VI's.  When you get a voltage reading, just multiple by the inverse of the voltage reduction factor from the voltage divider.

Chris Bakker
SET Americas
CEO

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