How do I separate AC and DC signals from phone line to go to 2 circuits

[moffy]

Should also consider hall effect clamp on meter, as it will detect DC magnetic fields. But the sensitivity is not great so you would probably need several turns of telephone wire (just 1 not both) to get milliamp accuracy. Saturable TX would be the same, the hall effect idea is simpler.

 

[Bobby Cooper]

Hello Again KeepItSimpleStupid and moffy,

I did some research on the Saturable Core Transformer can could not find one locally or even on line that was smaller than the size of a car battery. And, I also checked Google Patents and someone has the patend on this techology. So with frustration comes options to open new doors.

I think I can use the -48vdc (contact) to delatch the relay. i can use a "Self-Delatching" circuit confined to a separte relay board but, not connected to my Ring Detection Board. Here is the process I think will work:

A. Phone is ON-HOOK with -48VDC, relay is open isolating phone line from my home.

B. A phone call comes in:

On a Separate Relay Board that is connected to the phonline wires:

90VAC by induction excites the sense Transistor attacted to the inductor L1

1. The relay is tripped close and phones begin to ring.
   
2. Phone is answered - line voltage drops from -48VDC to -20VDC (OFF-HOOK Voltage)
3. The relay is latched only by a transistor that will desaturate (opto-isolated) when the -48VDC returns to the phone line.
   
4. Phone is hung up - line voltage increases back to -48VDC
5. Relay is de-energized (Return to A. Above.)

Do you guys think this would work ?

Using a DTDP relay rated at 120VAC has to be connected to the phone line to provide isolation and must have at least 800 Ohms of resistance per FCC Regs.

So I need a self-contained automatic Latching / De-latching relay circuit connected to the phoneline wires to handle isolation / pass-through / reset of relay.

My Spark Core Micro-controller Isolation / Detection board will only use the 90VAC Only by induction for automation / monitoring / logging call info.

 

[moffy]

So if I understand this:
1. The relay is latched if there is 90vAC or line voltage falls to 20v.
2. Relay is delatched if neither of the above.

Also found this:

could do the current sensing.

 

[Bobby Cooper]

I did some research on the Saturable Core Transformer can could not find one locally or even on line that was smaller than the size of a car battery. And, I also checked Google Patents and someone has the patend on this techology. So with frustration comes options to open new doors.

I think I can use the -48vdc (contact) to delatch the relay. i can use a "Self-Delatching" circuit confined to a separte relay board but, not connected to my Ring Detection Board. Here is the process I think will
work:

A. Phone is ON-HOOK with -48VDC, relay is open isolating phone line from my home.

B. A phone call comes in:

On a Separate Relay Board that is connected to the phonline wires:

90VAC by induction excites the sense Transistor attacted to the inductor L1The relay is tripped close and phones begin to ring.

Phone is answered - line voltage drops from -48VDC to -20VDC (OFF-HOOK Voltage)The relay is latched only by a transistor that will desaturate (opto-isolated) when the -48VDC returns to the phone line.

Phone is hung up - line voltage increases back to -48VDC te relay is de-energized and phone line is isolated from GRID and waiting for another call.

Do you guys think this would work ?

Using a DTDP relay rated at 120VAC has to be connected to the phone line to provide isolation and must have at least 800 Ohms of resistance per FCC Regs.

So I need a self-contained automatic Latching / De-latching relay circuit connected to the phoneline wires to handle isolation / pass-through / reset of relay.

The Spark Core Micro-controller Isolation / Detection board will only use the 90VAC Only by induction for automation / monitoring / logging call info

1. The phoneline could be locked out by Smartphone from anywhere in the world.
2. The core could notify a user by Smartphone that the status of their phoneline.

This will work for both Landline and VOIP phone systems.

Should I go this way ?

A small separate Relay Board that is isolated form the Spark Core that will automatically close the relay on a Ring of 90VAC from phoneline. then Delatch automatically when the Line voltage returns to -48VDC ?

 

[Bobby Cooper]

So if I understand this:
1. The relay is latched if there is 90vAC or line voltage falls to 20v.
2. Relay is delatched if neither of the above......

moffy, actually -

1. The relay will latch and stay latched when a phone call comes in.
2. The phones ring. (If not picked up the system will auto reset).
3. If phone is picked up - Relay will stay latched until phone hung up.
4. Phone hung up goes to "ON HOOK" State of -48VDC
5. Relay is now opened again / phone line isolated / waiting for call to ring and repeat cycle.

 

[moffy]

I have put together a small simulation for the telephone line. To run it:
1. Download LTSpiceIV from: https://www.linear.com/designtools/software/#LTspice
2. Download this simulation file to your computer.
3. Open the simulation with LTSpiceIV.
4. Run it. Press the little running man on the icon bar.
5. Probe the outputs. Just move the mouse to a wire until it changes into a probe then click it.

This is just a starting point but is very useful as you can test ideas very easily.

 

[KeepItSimpleStupid]

This will work for both Landline and VOIP phone systems.

Bobby:

Look up the term REN, for Ring Equlivelency Number. It USED to be the number of phone the line could ring. e.g. Standard 500 sets. I BELIEVE It's aroud 5-6 for POTS and maybe 2-3 for some VOIP systems.

Since ring is detected with an optocoupler, the 1 telephone of yesteryear might be 10 of today. The Network interface device itself typically has a 1/2 ringer in it.
It presents a load to the POTS line for circuit testing.

Generally, you add all of the numbers up on the devices that ring to see if your within the limit.

The REN for a particular VOIP provider was hard to obtain and the telco one is from memory.[/quote]

 

[Bobby Cooper]

I have a question ?

Can't I use a 20V diac ? (To allow a phone call to be isolated from the phone Company as On Hook volage is 48V (blocking Call) When Answered phone line voltage dropps to arounr 6-10vdc and will remain until hung up; returning to 48VDC diconnecting the Diac.

Phone Rings 90VAC (routed by my inductive detection + relay) + 48VDC ---> Phone is answered --> 10VDC !

S1 will be SSR.

The DIAC would be parallel to a Relay

 

[moffy]

I have revised my circuit to provide both ring and off hook detection separately:

I cannot see the purpose of the DIAC. When the phone is HUNG UP the switch inside is OPEN/Isolated.

 

[Bobby Cooper]

I have revised my circuit to provide both ring and off hook detection separately:

I cannot see the purpose of the DIAC. When the phone is HUNG UP the switch inside is OPEN/Isolated.

moffy, your absolutely correct - I got the DIAC function reversed and it won't work and Thanks for updating your schematic to include what I was beating my head on the wall about today. Off Hook State !!

I will incorporate your circuit in to my updated schematic below tomororw after I look at it very carefully tomorrow and see if I did it correctly.

Also, Feel free to tell me if I have it wrong on my 555 Monostable Design below. (I will be testing it this weekend).

After great thought and some testing the Hall Sensor for 20ma is not going to work on a phone line.

So, I extended my Phone Isolation Circuitfrom just Ring sensor to include a 555 Timer, Solid State Relay, Telco line signal indicator but, I am stuck and need your help (when you have time).

1. Should I include at "A" (on schematic below) a Bridge Rectifier Circuit to remove any AC from "Telco Line Signal Transistor ---> 555 Timer ciruit.
   
   
2. Should I provide at "B" (on schematic) isolation between Telco Line signal & 555 (Spark Core MCU) using the 4n28 PhotoTransistor OptoCoupler here @ "B"?
   
   
3. Your circuit as updated will allow me to detect Off Hook and let my Spark Core MCU see the state of the line.

?? I wonder if I will need to put a "Bleed" - current draw resistor across the SSR contacts so when no phones are being used the line can return to 48VDC - true state. So a dial tone will be present and SSR can be closed by my Spark Core MCU to allow a call from my house ?

 

[Bobby Cooper]

moffy, That update or your design is awesome and I need to think about it a lot tomorrow.

Then come back with an idea to run by you on how to get your Off Hook Detection circuit in to my current Schematic for testing.

Then 2nd run testing using your Ring Detector (replacing my design).

There is a caveat that I need to keep on my circuit design. Both Ring & Off Hook Detection Circuits need to be separate so I can run the Ring Detection purely by 3.3v from my MCU And, Run the 4N28, 555, SSR, with external 5VDC but, use a common Ground.

Also, another reason to have them separate is so I can change from one type circuit to another very easily. I can switch out your On Hook Dection to a LM339 Comparator so I can test for Current use been all circuits. Also, AC is okay for the Ring Circuit and Not so okay for the Off Hook Circuit. Also, If I need to have separate boards for the two dection circuits it will be easier to do that as well. Then there is my lack of knowledge to build what you have built.

I am considering using a Bridge Rectifier or a single 1N4007 Diode before "A" on my schematic and "B" the 4N28 to remove AC from the circuit.

? And, there is no way to assure proper polaraity on a phone line from the phone company. Wires get switch by technicians all the time in the field boxes.

Most circuits I see for Teleco connections use Isolation & Zener Diodes to correct the Polarity issue in a circuit. (I think) I will research this unless you already know the fix ?

Thanks. I am very impressed with your circuit. Very Nice.

Let me know if my ciruit does not make sense and what should I be working toward to make it better. Thanks, Bobby

 

[KeepItSimpleStupid]

I think you can be reasonably assured that at the NID, the polarity is correct. One standard touch tone phone would not tone if it was installed backwards.

Yea, your circuit should either work, or at least not get destroyed by the wrong polarity.

It's what the uneducated do inside the house. They connect wires until it works.

 

[Bobby Cooper]

I think you can be reasonably assured that at the NID, the polarity is correct. One standard touch tone phone would not tone if it was installed backwards.

Yea, your circuit should either work, or at least not get destroyed by the wrong polarity.

It's what the uneducated do inside the house. They connect wires until it works.

I worked in Iowa & Oklahoma where "Contrators" are allowed to service phone lines and repair them. It does not happen much but, connections in vaults and field cans do get crossed. Sure, they are suppose to make sure but, it does not always happen. 300+ group cable being put back together because of a back-hoe operator can lead to mis-matched polarization.

I could put a Green/Red LED in my circuit to take the guess work out of it for non-techie's as my board will be plugged in to the 1st junction outlet and not the Dmark Box.

 

[Bobby Cooper]

This Schematic is the pre-development of the proto-type. It will be scaled back as functions are replaced by the Spark Core MCU via Software Control.

Its a work in progress and all comments are welcome. What else needs to be detected beyound Ring & Off Hook state ?

 

[KeepItSimpleStupid]

I was searching for other stuff and came across this: https://www.ti.com/product/DRV411 But, anytime you put toroids into the mix, stuff gets expensive,.

It's like saying, it's possibe https://en-us.fluke.com/products/all-accessories/fluke-i30.html#techspecs but not cheap at least for calibrated sensors. And 0-100 mA by the clamp method. https://en-us.fluke.com/products/ma...e-772-process-calibration-tool.html#techspecs

So, I guess what I;m saying is that you could use a non-evasive hall effect technique to get on hook, off hook and ring. How and how many $, I don;t know.

PS: Did you include the possibility of someone not hanging up. You get the yucky tone and then your essentially hung up by the CO?

 

[Bobby Cooper]

[QUOTE="......PS: Did you include the possibility of someone not hanging up. You get the yucky tone and then your essentially hung up by the CO?[/QUOTE]

Thanks for the comments - I am not saying that the finish product will not use a hall effect sensor or such to detect Ring, Off Hook, On Hook but; it still may.

And, the C.O. does not disconnect from phones left off the hook anymore. They simple just pass them to the NSA for recording for profit.

 

[moffy]

Updated ring detector. Should be more discriminating in only responding to a ring.

 

[Bobby Cooper]

Updated ring detector. Should be more discriminating in only responding to a ring.

Thanks for the update. It will be Sat Afternoon before I can start looking at the values & numbers in your circuit. I have some other pressing work tomorrom; sleep too.

I was wondering. Could this be made to detect above 15vdc and below 11vdc ? Here is why I ask as this would be good numbers for the phone line too.

Say, I use this circuit in my car to monitor the car battery & charging system. It would also would dectect any current change after no curent change in, say, 5 mins. It current changes without the AC from the alternator (ring circuit) an alert can be sent to my smart phone via wifi. This would only work in my garage of if I was close and my Spark Core MCU was connecting via my hotspot on my phone.

Now, here is why I think this would be really cool - multipurose use. If a device is designed to be used in an automobile, NO FCC Certification required.

What else could it monitor on a car, RPM of the Engine ? (perhaps) Headlights left on with ignition off --> buzzer

Let me know what you think ? What would it take to make this circuit do both ? Using External Sensor Boards where need is a good option.

 

[moffy]

Horses for courses. Different applications require different solutions. Check that it works first on a phone line.

 

[Bobby Cooper]

Will do ! This coming weekend. Thanks