Hello - I am new to your forum and I did do some searchin before asking. Not sure exactly how to search this question though.

I would like to "De-latch" a "Self-Latched" DTDP realy being held closed by a latch cicuit going through one side of the Relay contacts.

When the phone is hung up and the telephone line returns to -48VDC "ON-HOOK" state I need for the relay to de-latch, de-energize and open both contacts.

The Off-Hook voltage is -20VDC but, goest up to -48VDC in ON-HOOK state (Phone is hung up).

Let me know if I need to post additional information.

 

You could use a voltage sensing relay or circuit, to open a contact in the latch circuit, when voltage changes.
But then that's what you're asking.

What latches the relay?

 

You could use a voltage sensing relay or circuit, to open a contact in the latch circuit, when voltage changes.
But then that's what you're asking.

What latches the relay?

Hi inwo - glad to see your reply to my question.

The relay is closed by a non-contact inductive pickup that detects the 90VAC (USA) Ring voltage in my phone line.

See Board Below that I have build and it does detect and provides ground for via a transistor circuit.

The line is disconnected from the grid by the open relay prior to getting a call.

<<<< Easy to build this circuit >>>
Once the Relay is closed by the 90VAC ring pulse for 60 seconds and it is timed by a 555 timer cirucuit. The Relay is a DTDP 120VAC.

<<< This is where I need assistance >>
if a phone is answered within that 60 seconds the line voltage will go from -48VDC "ON-HOOK" to -20VDC "OFF-HOOK" and the Relay remains latched close.

As soon as the phone is hung up the -48VDC causes the relay to open. (Zener Diode Cicuit & Transistor controlling ?)

This Circuit is the Below PCB Board:
(It is based on the next Non-Contact Ring Detector Circuit)

My non-contact ring detection board that does work (adjust wire wraps - good to go)

 

If you can build that much, unlatching the relay seems trivial.

Or must this be non-contact voltage sensing?
If voltage sensing is down stream from relay, it will not load the telco line while in standby.

Can you post a drawing of the relay and latching circuit?

This circuit is all powered from 9V rather than telco?

 

Not really knowing your circuit!
Ignoring telco impedance and ring voltage "off hook".
Latch signal must remain until off-hook voltage goes below Z.

 

If you can build that much, unlatching the relay seems trivial.

Or must this be non-contact voltage sensing?
If voltage sensing is down stream from relay, it will not load the telco line while in standby.

Can you post a drawing of the relay and latching circuit?

This circuit is all powered from 9V rather than telco?

moffy, I'll work up a drawing this evening of the circuit for latching.

I can use contact telco voltage to power a de-latch circuit for the relay. However, it has to be a non-polarized circuit. Will spend many hours on this today and tomorrow to get closer to a workable solution.

Thanks.

 

Nice little modem module!

Where is that from?

 

Nice little modem module!

Where is that from?

The White board is a Cortex M3 Powered Mico-Controller with builtin 802g Wifi for $39 and its called the Spark Core. The darker board is mine and I call it a Phone Isolation Shield "PIS".

Right the only thing the PIS does is to sense telephone line power and lights an LED. Its a work in progress.

 

Did you look at the diagram?

There may be better ways to do it. Need to know if that's the function that you want.

Your relay/555 diagram would be helpful.

 

inwo, Yes - you are correct about better ways and with my limited skills I am seeking suggestions. Current Sensing VDC is going to be difficult at 20 - 50mA. I have come the conclusion I need to get 3 different voltages directly from the phone wire and it shouldn't be a problem as I am going to design this for VOIP Application (Different Rules) and have 3 POTS that can be adjusted for backward compatability with Land Line Phone System (North America).

What would you suggest for a circut to convert the 3 voltages to Analog signals for my Sprak Core MCU ?

0 - 90VAC (RING)--- Bridge Rectifier ---> Opto Isolation, say a 4N25 or 4N28 --> ?? --> Analog Signal 0-3VDC. MCU Analog Pin 1

6VDC - 48VDC --> 4N28 --> ? --> Analog Signal 0 - 3VDC . MCU Analog Pin 2

Thanks for your help. Bobby