Searching \ for '[EE]: 1:1 transformer' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/power.htm?key=transformer
Search entire site for: '1:1 transformer'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: 1:1 transformer'
2001\02\11@024943 by pang khong lin

picon face
hi everyone,

good evening. I am designing a circuit that allows the user to
call in from anywhere and control appliances remotely using the phone.
There are several questions which i hope you will be able to enlighten me.

Most telephone/modem circuit uses a 1:1 dry transformer for impedance
matching purposes. These are also call 600:600 ohm transformer. Does that
means that as long as this transformer is plug-in, then it will provide a
600 ohms impedance to the telephone line? If this is not true then that
means external components is needed and basically the transformer can then
be 700:700, 800:800, etc ?

I am using ETAL P3191 and the datasheet provides the matching
recommendations
                                          _____________
   -----600 ohm-----o------- 6.8 uF -----|             |-------|-----
  |                                      |             |       |
  |                                      | Transformer |       |
Line Source                               |             |    430 ohm
  |                                      |             |       |
  |                                      |             |       |
   ----------------o---------------------|_____________|-------|-----


Must the cap value be follow completely? 6.8uF at 250V is very expensive. I
saw some design and found that every one is using
different values. Are there any calculations involve? if i plan to use a
0.68uF,is it ok?

In addition, to generate the off hook condition, i have to put a resistor
across the phone line ( before the cap ) of around 500 ohm. I have tested
and  found that any value in between 0 ohm and 1.5 Kohm can do the job. Does
this method of generating off hook condition affect the impedance?

I connected a DTMF decoder encoder ( MC145740 ) at the transformer
secondary and presently, i am not able to detect any valid DTMF from the
IC.In your opinion what would be the error over here? ( I uses a relay to do
the switching to on hook and off hook circuitry )

Thanks a lot.


_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2001\02\11@050700 by Chris Carr

flavicon
face
Have a look at the following

http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html

Chris


{Quote hidden}

Does
> this method of generating off hook condition affect the impedance?
>
> I connected a DTMF decoder encoder ( MC145740 ) at the transformer
> secondary and presently, i am not able to detect any valid DTMF from the
> IC.In your opinion what would be the error over here? ( I uses a relay to
do
{Quote hidden}

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2001\02\11@195323 by Jane Ifurung

picon face
hi! i did some interfacing to telephone line and phone
units before, just a year ago. i used the Mitel
Semiconductor's SLIC(Subscriber Line Interface
Circuit). I think the part no. is MH88617. It can
detect the ringing, on/off hook condition, the
dialing, the line interfacing with just some external
components. The 600:600 ohms for the transformer
(called the isolation transformer) is recommended
since the common phone line impedance used by the
industry is 600 ohms (depends with line length,
though). You can try seeing transformers at Midcom.
They gave me samples before. Hey! I'm from the
Philippines and Midcom is from United States! Trust
me, they're very kind.

Jane P.Ifurung

--- Chris Carr <spam_OUTnyedTakeThisOuTspamBTINTERNET.COM> wrote:
> Have a look at the following
>
>
www.hut.fi/Misc/Electronics/circuits/teleinterface.html
{Quote hidden}

----------------o---------------------|_____________|-------|-----
{Quote hidden}

_________________________________________________________________________
{Quote hidden}

__________________________________________________
Do You Yahoo!?
Get personalized email addresses from Yahoo! Mail - only $35
a year!  http://personal.mail.yahoo.com/

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2001\02\11@201857 by David VanHorn

flavicon
face
At 04:52 PM 2/11/01 -0800, Jane Ifurung wrote:
>hi! i did some interfacing to telephone line and phone
>units before, just a year ago. i used the Mitel
>Semiconductor's SLIC(Subscriber Line Interface
>Circuit).

I'd be interested to know how you did this.

SLICs are designed to go on the other end of the line.
IOW, they are supposed to BE the phone company.

--
Dave's Engineering Page: http://www.dvanhorn.org
Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2001\02\12@032740 by Chris Carr

flavicon
face
> I am using ETAL P3191 and the datasheet provides the matching
> recommendations

If you have a look at the Etal Website http://www.etal.ltd.uk/

you will find most of the information you require including an Application
Note on  Gyrators.

Chris

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


More... (looser matching)
- Last day of these posts
- In 2001 , 2002 only
- Today
- New search...