[sci.electronics] I need a telephone ring detector chip

mzabeti@phoenix.UUCP (04/15/87)

If you have seen this posting before, pardon me, I didn't think it made it out
of the local area.

Is there a chip out there that would detect a telephone ring by outputing a
signal?  Like have an output pin that goes high for the duration of each ring
and then goes back to low.  I am sure there must be such a thing since modems
count how many rings they get before answering.

I would be using that chip to hook it up to my phone line, and have a room
light be turned on after the phone has rung 11 times(if nobody answers the
phone).

Thank you for your help.

                        Mahboud
--
Mahboud Zabetian                allegra! --\    zabetia@tiger.princeton.edu
232 Pyne Hall                   mhuxi! -----\           (609) 452-2285
Princeton University            seismo! -----\          (609) 734-0246
Princeton, NJ 08544             attunix! ------ princeton!zabetia

fish@ihlpa.ATT.COM (Bob Fishell) (04/17/87)

> Is there a chip out there that would detect a telephone ring by outputing a
> signal?  Like have an output pin that goes high for the duration of each ring
> and then goes back to low.

The best thing to use for this application is an  opto-isolator, so that
your circuit has no direct electrical connection to the phone line.
Any non-FCC approved device connected to your phone line is illegal, by
the way, so the following is offered in theory only.

The ringing voltage is about 90vac, and is applied at 20Hz, 2 seconds
on, and 4 seconds off.  You will want a DC-blocking diode and a
suitably large resistor in series with the isolator's input, so as to
bring the current down to within the specifications for the device. If
you want  a pulse for each ring, connect a large capacitor accross the
output of the opto  isolator through a suitably large resistor. Choose a
combination  with a time  constant greater than ~50ms and less than ~1 s.  
You can drive CMOS with this  directly  (OK, you've got lousy rise
and fall times -- CMOS is forgiving). If you want to use TTL (though I
can't imagine why), you'll have to  shmitt-trigger the output to clean
it up.
-- 
 __
/  \				Bob Fishell
\__/				ihnp4!ihlpa!fish

jpexg@mit-hermes.UUCP (04/18/87)

In article <228@phoenix.PRINCETON.EDU>, mzabeti@phoenix.PRINCETON.EDU 
(Mahboud Zabetian) writes:

> Is there a chip out there that would detect a telephone ring by outputing a
> signal?  Like have an output pin that goes high for the duration of each ring
> and then goes back to low.  

A quick and safe way to do this is to use an optoisolator (MCT-2 or IL-5 are
cheap and easy to find) across the line in reverse-parallel with a diode and
with the combination in series with a capacitor (try .01 mufd or so, and use 
bigger ones till it works). This is a good setup because telephone ring
voltage is ~90 volts--not what your logic wants to see, and you also don't
want anything you might do to zap the phone line. You'd need a 1-shot on 
the output (or a suitable filter) to make the transient blips from the 
isolator into a steady signal. Make sure the capacitor can handle >90 volts!

henry@utzoo.UUCP (Henry Spencer) (04/20/87)

The following circuit is from an HP app note; I have tested it and found
it to work well.  Sorry for the inability to just display the diagram, but
I lack the patience to try to approximate it with ASCII characters...

You have two wires coming in from the phone line.  First, each goes through
a 100k resistor.  Then there is a 10M resistor between them.  Then one of
them goes through a 0.02 uF capacitor, which should be rated for something
like 200V.  Then there are two diodes in parallel between the lines, with
opposite polarities (one with anode to top line, the other with cathode
to top line):  one a 1N4148 and one the input LED of a 6N139 opto-isolator.

The 6N139 has a Darlington output with four pins available.  The one going
to the photodiode and the collector of the inner transistor goes to +5.
The one going to the emitter of the outer transistor goes to ground.  The
one going to the collector of the outer transistor is the output.  The one
going to the internal transistor-transistor connection is connected to the
output through a 0.1 uF capacitor.

The output line then goes through a 10k resistor.  Then there is a 56k
resistor from it to +5.  Then it goes into the base of a 2N3906 transistor.
The emitter of this transistor is connected to +5.  The collector is the
final output, with a 1k pulldown resistor between it and ground.

Explanation:

The 100k resistors supply plenty of impedance between the whole 
circuit and the lines no matter what fouls up inside the circuit.  The
10M resistor bleeds off static charges that might show up when the thing
is not connected (HP actually made it 22M, but that's hard to find and
10M works fine).  The 0.02 capacitor blocks DC completely and also gives
quite a bit of AC impedance; it needs to be rated for a nice high voltage
because the ringing AC is close to 100V and you want a good safety margin.
The 1N4148 conducts when the AC voltage is the wrong polarity for the LED
to conduct; leave this out and the opto will try to block the full ringing
voltage at those times, which will fry it.

The 0.1 capacitor between the internal node and the output acts as an
integrator, so that the AC ringing shows up as one pulse rather than a
sequence of short ones.  It also gets rid of smaller and less frequent
activity like dialing pulses.  The 10k resistor limits current through
the opto and transistor when the opto is on.  The 56k resistor pulls
the transistor's input up high when the opto is off.  And the 2N3906, in
conjunction with the pulldown resistor, amplifies the output signal.

This circuit isn't particularly fussy about power voltage, although you
might want to increase some of the resistor values on the output side
for higher voltages.  The output is certainly CMOS compatible and is
probably TTL compatible, although I haven't done the numbers to be really
sure about the latter.  The 6N139 is a premium opto and will cost a few
bucks, but overall it's not what you'd call an expensive circuit, given
the logic-level output and the high degree of isolation from the phone
line.
-- 
"If you want PL/I, you know       Henry Spencer @ U of Toronto Zoology
where to find it." -- DMR         {allegra,ihnp4,decvax,pyramid}!utzoo!henry

rbl@nitrex.UUCP ( Dr. Robin Lake ) (04/20/87)

In article <228@phoenix.PRINCETON.EDU> mzabeti@phoenix (Mahboud Zabetian) writes:
>
>
>Is there a chip out there that would detect a telephone ring by outputing a
>signal?  Like have an output pin that goes high for the duration of each ring
>and then goes back to low.  ...
>

Texas Instruments' latest broadside, called "Circuit Innovations"(?) perhaps,
announced a line of about 6 ring detector ciruits, some with overvoltage
protection and some with sound generators of various frequencies.  Their
local distributor or 800-number would produce spec sheets.

Rob Lake
decvax!cwruecmp!nitrex!rbl

wolfgang@haddock.UUCP (04/22/87)

>You have two wires coming in from the phone line.  First, each goes through
>a 100k resistor.  Then there is a 10M resistor between them.  Then one of
>them goes through a 0.02 uF capacitor, which should be rated for something
>like 200V.  Then there are two diodes in parallel between the lines, with
>opposite polarities (one with anode to top line, the other with cathode
>to top line):  one a 1N4148 and one the input LED of a 6N139 opto-isolator.

One minor point: The 10 meg 'bleeder' resistor could cause problems.
Some telephone line integrity tests involve measuring minute leakage
currants. Leakages in that range (<100 meg) are usually indicative of
brittle insulation on the line pairs. This could cause some repair
folks to investigate the source. (I'm not sure why the apps note
engineer felt he needed a bleeder. The capacitor has 200k in series
with it, and is only charged to 50 volts max. Not what you'd ever call
a shock hazard.)

Back (long before divestiture) when MaBelle still cracked down hard on
extra ringers on the line, I built an opto isolator out of an ne-2
(neon) bulb, series capacitor and resistor. I used a photo-darlington
for the detector. Talk about low load on the phone line.
-- 
Wolfgang Rupprecht 			haddock.ISC.COM!wolfgang

rmrin@inuxh.UUCP (04/23/87)

> >You have two wires coming in from the phone line.  First, each goes through
> >a 100k resistor.  Then there is a 10M resistor between them.  Then one of
> >them goes through a 0.02 uF capacitor, which should be rated for something
> >like 200V.  Then there are two diodes in parallel between the lines, with
> >opposite polarities (one with anode to top line, the other with cathode
> >to top line):  one a 1N4148 and one the input LED of a 6N139 opto-isolator.
> 
> One minor point: The 10 meg 'bleeder' resistor could cause problems.
> Some telephone line integrity tests involve measuring minute leakage
> currants. Leakages in that range (<100 meg) are usually indicative of
> brittle insulation on the line pairs. This could cause some repair
> folks to investigate the source. (I'm not sure why the apps note
> engineer felt he needed a bleeder. The capacitor has 200k in series
> with it, and is only charged to 50 volts max. Not what you'd ever call
> a shock hazard.)
> 
Ten megs will not cause any problems.  I would suggest builiding a circuit
such as this in a metal box to guard against component overheating in the
event funny voltages get on the phone lines.

richard@islenet.UUCP (Richard Foulk) (04/25/87)

The March '87 issue of Modern Electronics has a construction article
on page 48 for a "solid-state telephone bell replacement and stand-
alone incoming-call annunciator".

It seems to go into all the necessary details.

-- 
Richard Foulk		...{dual,vortex,ihnp4}!islenet!richard
Honolulu, Hawaii	or ...!islenet!bigtuna!richard

larry@kitty.UUCP (Larry Lippman) (04/27/87)

In article <565@inuxh.UUCP>, rmrin@inuxh.UUCP (D Rickert) writes:
> > >You have two wires coming in from the phone line.  First, each goes through
> > >a 100k resistor.  Then there is a 10M resistor between them.
> > ...
> > One minor point: The 10 meg 'bleeder' resistor could cause problems.
> > Some telephone line integrity tests involve measuring minute leakage
> > currants. Leakages in that range (<100 meg) are usually indicative of
> > brittle insulation on the line pairs. This could cause some repair
> > folks to investigate the source.
> 
> Ten megs will not cause any problems.

	A few facts:

1.	# 22 AWG telephone cable insulated with polyethylene (PIC), with
	"perfect splices", has a conductance of about 0.05 mho/per mile. 
	A 2 mile loop would have a "theoretical" leakage resistance of
	about 10 megohms.

2.	# 22 AWG telephone cable insulated with pulp (i.e., paper), with
	"perfect splices", has a conductance of about 0.1 mho/per mile. 
	A 2 mile loop would have a "theoretical" leakage resistance of
	about 5 megohms.

	In reality, outside cable plant will never achieve such high leakage
resistance due to moisture present in cable splices and outside cable
terminals.  While pulp-insulated cable is almost always pressurized with
dry air or nitrogen, there is still enough moisture present to halve the
above value.  The same concept holds true for polyethylene cable.  A
gel-filled cable (usually called "icky-pic") does somewhat better, but
we are still in the same ballpark.
	Just _opening_ a pulp-insulated cable slice on a warm, humid day,
with consequent loss of pressurization can reduce leakage resistance to
well under 1 megohm.
	An actual cable fault, caused by presence of gross amounts of
water which wets a splice, can drive insulation resistance to << 100,000
ohms.
	So, the point it: most telephone companies set Automatic Line
Insulation Test (ALIT) apparatus to alarm at well under 100,000 ohms
leakage resistance, since: (1) there is such a large leakage variation
in subscriber loops; (2) no serious problem develops until leakage
resistance becomes << 100,000 ohms; and (3) to minimize false alarms.
Threshhold values used by one operating telephone company are 67,000
ohms leakage for "minor" alarm, and 43,000 ohms leakage for "major"
alarm.
	A "truly" wet splice may measure < 10,000 ohms leakage resistance,
so these ALIT threshholds are set to minimize false alarms.
	There are basically two types of ALIT tests: (1) leakage from
TIP to RING, and (2) leakage from either conductor-to-ground.  Most ALIT
apparatus can perform both types of tests.  Since there are many weird
telephones on the market which draw a small amount of current in an on-hook
state to power dialer memory, clocks, etc., most ALIT testing is done
from conductor-to-ground only to mimimize false alarms.
	
	So, to get back to the original issue, 200,000 ohms across TIP and
RING has always been considered a "safe" subscriber instrument leakage
value (historical reference: "old" HZM voice-connecting arrangement).
The two 100,000 ohm resistors suggested by the TI app note is an ideal
arrangement.
	While ALIT apparatus may use a higher threshhold for ground leakage,
we are not talking about ground leakage in a ring detector circuit (except
in some key telephone units, but that's another story...).

> I would suggest builiding a circuit
> such as this in a metal box to guard against component overheating in the
> event funny voltages get on the phone lines.

	I wouldn't worry about overheating.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
<>  UUCP:  {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry
<>  VOICE: 716/688-1231        {hplabs|ihnp4|mtune|seismo|utzoo}!/
<>  FAX:   716/741-9635 {G1,G2,G3 modes}    "Have you hugged your cat today?" 

greg@utcsri.UUCP (04/28/87)

In article <565@inuxh.UUCP> rmrin@inuxh.UUCP (D Rickert) writes:
>Ten megs will not cause any problems.  I would suggest builiding a circuit
>such as this in a metal box to guard against component overheating in the
>event funny voltages get on the phone lines.

In order to dissipate 1/4 W in a 10M resistor, you have to apply 1,581 V
across it. And the 10M resistor will dissipate 98% of the power in the circuit.

The capacitor will fry long before the resistors get warm.


-- 
----------------------------------------------------------------------
Greg Smith     University of Toronto      UUCP: ..utzoo!utcsri!greg
Have vAX, will hack...

wtm@neoucom.UUCP (04/30/87)

A few years back I took an EE course on machinery.  A safety
indoctrination was imposed on us in the lab so that  we would
respect the equipment.

The instructor claimed that the lowest known substantiated voltage
to have caused death by electrocution was 56 vdc.  He didn't offer
any documentation, but it seems believable that you could get
enough current to stop your heart under prine circumstances such as
stnading in salt water and grabbing wires very tightly.

I seriously doubt that a poor little .22 uF capactior charged up to
50 volts would have much chance at being lethal, as long as it was
disconnected from the original voltage source.

  --Bill

Bill Mayhew
Division of Basic Medical Sciences
Northeastern Ohio Universities' College of Medicine
Rootstown, OH 44272  USA    phone:  216-325-2511
(wtm@neoucom.UUCP   ...!cbatt!neoucom!wtm)