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E&M Telephony
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rickman
Jan 19, 2017, 2:08:37 AM1/19/17
to
It has been a long time since I designed any telephony equipment. I
know the E&M circuits are simple conceptually, but there are any number
of real world issues that impact the design, which I can't remember much
of.
The battery voltage is approximately 48 volts and the circuits are
current limited. Control is done with relay contacts in the old days
and sensing was done with a relay coil. Now I'm sure that has all been
replaced with a few transistors. I tried looking for ICs that would
handle this, but came up empty handed. Is there anything out there that
is designed for this? I know there are chips for the SLIC and such, but
I don't see anything for E&M.
This is not for a circuit to a CO, so there won't be exposure to
lightning or AC wire crosses. This will be between a PBX and networking
equipment (circuit to packet). I'm not sure it even needs 48 volts
since the interface is really current driven. Anyone know if E&M
typically uses a lower voltage these days like 12 volts?
--
Rick C
know the E&M circuits are simple conceptually, but there are any number
of real world issues that impact the design, which I can't remember much
of.
The battery voltage is approximately 48 volts and the circuits are
current limited. Control is done with relay contacts in the old days
and sensing was done with a relay coil. Now I'm sure that has all been
replaced with a few transistors. I tried looking for ICs that would
handle this, but came up empty handed. Is there anything out there that
is designed for this? I know there are chips for the SLIC and such, but
I don't see anything for E&M.
This is not for a circuit to a CO, so there won't be exposure to
lightning or AC wire crosses. This will be between a PBX and networking
equipment (circuit to packet). I'm not sure it even needs 48 volts
since the interface is really current driven. Anyone know if E&M
typically uses a lower voltage these days like 12 volts?
--
Rick C
Tim Wescott
Jan 19, 2017, 11:32:40 AM1/19/17
to
applications. Weigh my responses accordingly.
Is the audio channel on E&M wet? Or are you talking about the signaling
wires?
I'm surprised there's modern telco systems out there that would prefer to
run a bunch of E&M trunks someplace rather than just a fiber -- I have
this vision of fiber run to a little beige box just outside the building,
then 20 feet of trunk lines into a PBX that has no excuse not to have a
fiber connection.
I suspect that most people use solid-state relays, or perhaps they roll
their own SSR circuits. I'd like to say just use a MOSFET, but that
assumes that every telco gets the polarity right: it's probably a good
idea not to count on that.
--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com
Tim Wescott
Jan 19, 2017, 11:57:41 AM1/19/17
to
there's one thing I remember about working with telephony, it's that
almost nothing you can do will break those expensive wires stretched from
hither to yon, but getting good consistent operation out of the thing
depends on sticking to the BelCor standards (or whatever is used today).
tabb...@gmail.com
Jan 19, 2017, 2:07:30 PM1/19/17
to
NT
rickman
Jan 19, 2017, 3:15:39 PM1/19/17
to
On 1/19/2017 11:57 AM, Tim Wescott wrote:
> On Thu, 19 Jan 2017 10:32:30 -0600, Tim Wescott wrote:
>
>> On Thu, 19 Jan 2017 02:08:33 -0500, rickman wrote:
>>
>>> It has been a long time since I designed any telephony equipment. I
>>> know the E&M circuits are simple conceptually, but there are any number
>>> of real world issues that impact the design, which I can't remember
>>> much of.
>>>
>>> The battery voltage is approximately 48 volts and the circuits are
>>> current limited. Control is done with relay contacts in the old days
>>> and sensing was done with a relay coil. Now I'm sure that has all been
>>> replaced with a few transistors. I tried looking for ICs that would
>>> handle this, but came up empty handed. Is there anything out there
>>> that is designed for this? I know there are chips for the SLIC and
>>> such, but I don't see anything for E&M.
>>>
>>> This is not for a circuit to a CO, so there won't be exposure to
>>> lightning or AC wire crosses. This will be between a PBX and
>>> networking equipment (circuit to packet). I'm not sure it even needs
>>> 48 volts since the interface is really current driven. Anyone know if
>>> E&M typically uses a lower voltage these days like 12 volts?
>>
>> It's been 30 years since I've done any circuit design for telephony
>> applications. Weigh my responses accordingly.
>>
>> Is the audio channel on E&M wet? Or are you talking about the signaling
>> wires?
Signalling.
> On Thu, 19 Jan 2017 10:32:30 -0600, Tim Wescott wrote:
>
>> On Thu, 19 Jan 2017 02:08:33 -0500, rickman wrote:
>>
>>> It has been a long time since I designed any telephony equipment. I
>>> know the E&M circuits are simple conceptually, but there are any number
>>> of real world issues that impact the design, which I can't remember
>>> much of.
>>>
>>> The battery voltage is approximately 48 volts and the circuits are
>>> current limited. Control is done with relay contacts in the old days
>>> and sensing was done with a relay coil. Now I'm sure that has all been
>>> replaced with a few transistors. I tried looking for ICs that would
>>> handle this, but came up empty handed. Is there anything out there
>>> that is designed for this? I know there are chips for the SLIC and
>>> such, but I don't see anything for E&M.
>>>
>>> This is not for a circuit to a CO, so there won't be exposure to
>>> lightning or AC wire crosses. This will be between a PBX and
>>> networking equipment (circuit to packet). I'm not sure it even needs
>>> 48 volts since the interface is really current driven. Anyone know if
>>> E&M typically uses a lower voltage these days like 12 volts?
>>
>> It's been 30 years since I've done any circuit design for telephony
>> applications. Weigh my responses accordingly.
>>
>> Is the audio channel on E&M wet? Or are you talking about the signaling
>> wires?
>> I'm surprised there's modern telco systems out there that would prefer
>> to run a bunch of E&M trunks someplace rather than just a fiber -- I
>> have this vision of fiber run to a little beige box just outside the
>> building,
>> then 20 feet of trunk lines into a PBX that has no excuse not to have a
>> fiber connection.
carry the calls over Ethernet by whatever physical medium you have.
My boards go in the existing products this company offers, but they are
changing their business model from a hardware/software company to just a
software company. They are handing the hardware business (for this
product line) to another company and will only sell the software.
Strange but true! So my boards will no longer be used.
My contact with the company suggested I might be able to get a little
consulting business with the hardware company since they know nothing
about telephony. Unfortunately I don't remember much myself.
>> I suspect that most people use solid-state relays, or perhaps they roll
>> their own SSR circuits. I'd like to say just use a MOSFET, but that
>> assumes that every telco gets the polarity right: it's probably a good
>> idea not to count on that.
bridge to connect the current sensor. In some configurations power
comes from the PBX only, in others both ends source power. They don't
mix up the polarity, but it will change depending on the configuration,
type 1, 2, 3, etc.
> Oh -- and I'd design for at least 48V, just to be on the safe side. If
> there's one thing I remember about working with telephony, it's that
> almost nothing you can do will break those expensive wires stretched from
> hither to yon, but getting good consistent operation out of the thing
> depends on sticking to the BelCor standards (or whatever is used today).
--
Rick C
rickman
Jan 19, 2017, 3:16:11 PM1/19/17
to
--
Rick C
Hul Tytus
Jan 19, 2017, 6:02:07 PM1/19/17
to
There were numerous telephone projects in Popular Electronics and Radio
Electronics. Some were impressive phone systems. One was a doall board
that had all governmentally required features to serve as an interface for
whatever project the reader had in mind.
You may be able to find these on the internet and, if so, use them as a
model and a reminder.
Hul
Electronics. Some were impressive phone systems. One was a doall board
that had all governmentally required features to serve as an interface for
whatever project the reader had in mind.
You may be able to find these on the internet and, if so, use them as a
model and a reminder.
Hul
Bill Beaty
Jan 24, 2017, 12:32:22 AM1/24/17
to
On Wednesday, January 18, 2017 at 11:08:37 PM UTC-8, rickman wrote:
> replaced with a few transistors. I tried looking for ICs that would
> handle this, but came up empty handed.
Pull out the databooks, already must know keyword jargon. Search on: "LCA" line-card access, basically the solid state relays. Also the audio chip, "DAA" direct phone-line connection. I immediately hit these via digikey:
> replaced with a few transistors. I tried looking for ICs that would
> handle this, but came up empty handed.
http://www.ixysic.com/Products/LITELINK.htm
http://www.ixysic.com/Products/LCAS.htm
I recall that back in the 1990s (industrial sensors job) we were buying scads of CP Clare "Optomos" ssrs in dip-6 and dip-4 packages, which were cheap because of mass phone company buys.
CPC1000? Doesn't exist now, try CPC1002. If it's 4-pin surface mount, opto-isolated relay 60VDC half-amp mos output with LED input, it was probably developed as solid state version of a phone company mechanical relay.
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