Telephone line emulation

[pikstart]

Hi friends.

I am looking for a circuit to recreate a telephone line. It will be used to connect an Alarm system to a GSM module.

When PSTN line is cut, then a relay will change the connection of the Alarm telephone line to the GSM. For the Alarm to work, it needs to see a telephone line and the GSM needs seperate Mic and Ear signals.

I found a chip that could do that, but others ideas are welcome. The chip is the STLC3055 from ST. It is small size and needs over 5.5Volts to work.

I'd prefer to work on 5Volts only with PDIP devices or even better discrete.

Thanks,
Ioannis

 

[alec_t]

According to Yahoo the PSTN line voltages are:

on hook = -48VDC, off hook = ~12VDC, ringing voltage = 90VAC on top of the on hook 48VDC.

Perhaps you could just use a boost DC-DC switcher to derive both DC voltages from 5V and so simulate line presence if needed. And just monitor line DC voltage to detect a cut line.

 

[pikstart]

Thanks for bothering to reply. It is not so easy, obviously. I have to make an interface from 2 line current loop (the PSTN emulation) to 2 seperate signals for Mic input to GSM audio in and Ear. for GSM audio out. And also mix these with what you said about 48 and 12 volts. Fortunatelly, I do not need ring signal as it is not needed. The Alarm system will only call when there is a trigger and PSTN line is cut.

If the user want to call the Alarm, he/she will do it from PSTN line directly.

Ioannis

 

[WTP Pepper]

Why not use a bridge rectifier across the line via some high(ish) value resistors and put these into a differential amp. Detect the line voltage falling once a line is cut.
Be careful as if you load the line significantly, then you may have a Telco on your back as they use small currents pumped around the system to detect imminent line failure. It also will need lightning arrestors on the front end. I can dig out a cct if you require I used at my old house for just this.

Anything connected to a telephone line needs to have balanced inputs. You just cannot ground one side.

 

[pikstart]

Thanks for the post. But what I need is to re-create the Telephone line when it is cut. A relay will move the device (Alarm system) from the normal PSTN line to the local created line that will then be connected to a GSM module.

So, at the end, the Alarm will think it has a PSTN line, but in reality it will be connected through the GSM network.

The chip STLC3055 from ST is doing exactly that, but is hard to handle.

Ioannis

 

[alec_t]

Have you seen this?
https://www.google.co.uk/url?sa=t&r...ezsCVoV2g&sig2=yFgso6lXXlUJRUQYwu8okw&cad=rja

 

[Mike odom]

Have you seen this?
https://www.google.co.uk/url?sa=t&r...ezsCVoV2g&sig2=yFgso6lXXlUJRUQYwu8okw&cad=rja

sweet!

 

[pikstart]

Yes I have seen that. Thanks.

Ioannis

 

[KeepItSimpleStupid]

I did a really quicky telco line simulator when I was trying to fix a stupid phone. I just grabbed a 600 to 600 ohm transformer and did a 30 mA regulator with about 40 V or so. Worked.

There are IC's that monitor the telephone line and there are devices called a DAA or Data Access Arrangement with is a pre-certified module that will interface with the phone line.

Here is a very old device: https://www.electro-tech-online.com/custompdfs/2012/12/tca3388rev0.pdf

Here is a newer one: https://www.electro-tech-online.com/custompdfs/2012/12/CH1847_607-0021.pdf

Here is a bunch:https://www.cermetek.com/Catalog/Telephone-Line-Interface/

 

[Smartie]

I'm working on project at work that involves emulating the phone line, we've gone with using a ag1171 which is a Subscriber Line Interface Circuit or a SLIC. It has a built in DC to DC boost converter, and handles all the voltages and such. Should be what you're after

 

[pikstart]

Thanks K.I.S.S.

The TCA3388 is the one I think I want. But is not produced anymore.

Thanks anyway,
Ioannis

 

[pikstart]

Thanks Smartie. Where can I find this?

 

[Smartie]

Thanks Smartie. Where can I find this?

I'm not sure where my work gets them from, but a quick look online shows:
http://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=13904
http://www.aliexpress.com/store/pro...F-same-as-AG1171-AG1170/203008_535930990.html

There also appears to be similar variants with a different packaging, but have the same functionality.

 

[pikstart]

Great, thanks a lot.

Ioannis