Constructing a circuit that would trigger my cordless house phone intercom circuit?

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Buk

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I missed a delievery today because I was in the garden. I had one of the cordless handsets outside at the time, and it struck me that if my doorbell triggered the intercom function, I would have known they were there.

What's the likelyhood of working out what signal would be required; and building a circuit to send it?
 
A basic ring video doorbell is about $60. It will alert your mobile when anyone is present.
I assume your budget is less than $60?
 
I have plans of doing the following with a cordless phone.

I want to detect the last LED on the discreet bar graph sound indicator on a baby monitor. What I am doing right now, is I put the baby portion of a baby monitor next to a cordless phone sitting in a handset, It then amplifies the ring. I can determone if the ring is intercom (nurse call) or phone. I can take either adult unit outside. The parental unit is battery powered. The baby unit is not.

One parental unit is in my bedroom and the other is in the Laundry room. I get supplimental visual indication.
I should move that unit so it's visible from the bed. It's behind me.

"The plan" is put a detector on one of the parent units with a magnetic connector which gets connected to "a home made device"
I want to "detect" if the baby monitor has been triggered.

I also want to be able to differentiate the nurse call (intercom) and telephone. I'll do that differentiation with a DAA (Data Access Arrangement). I actually want to do more:
I need signals for:

#1. Nurse call
#2. land line ringing
#3 land line "off hook"
#4 land line "Off hook and no one talking for 10-15 minutes"

What I have right now, is a purchased device that connects to the telephone line and has a relay output. The relay is connected to an LED. The LED has a specific pattern when the phone rings. It's solid when it's off hook. It has some other pattern if there is voice mail which is a feature we don't have.

I really wanted "ringing" and "off hook for 15 minutes and not talking"

The plan is to turn these into lighted indicators and to automatically mute the TV.

You could interface to a lesser used cordless phone with the magnetic connector with a FET optocoupler to the intercom button.
If I used my cordless phone it would require pushing 3 buttons on the phone.
INTERCOM - SELECT Global Page - OK

it would be considerably harder to do a voice announcement.

There are systems that do use the phone and have an intercom to lock/unlock the door.
Here https://vikingelectronics.com/products/c-3000/ is just an example.

There's one that the doorbell causes the phone to ring with a distinctive ring. You then answer it and talk using a phone. You can then use touch-tones to unlock the door. No video.

I usually take the baby monitor outside rather than my cell. It's louder.
 
Last edited:
Buk said:
What's the likelyhood of working out what signal would be required; and building a circuit to send it?
Click to expand...
The circuit part is relatively simple. Domestic doorbells run on low voltage AC. An optocoupler, 2 resistors, and one capacitor will give you an isolated two-state signal indicating a button press. That can drive any kind of interface circuit needed.

The problem is the cordless phone handset. Based on ***zero*** information, it probably has a microcontroller inside that runs all signalling and function selection. Mine have an LCD screen with three text lines. Getting it into Intercom mode takes a total of 6 button presses on two buttons to get through the menu selections to the Intercom mode. That is a difficult thing for an external circuit to activate.

ak
 

And at the other extreme, some DECT phones have a "locate" button on the base unit that makes all handsets ring until cancelled - a relay contact or optocoupler could easily pulse that to trigger ringing.

It very much depends on the phone system.


Do you have a home automation system? You can get such as a Fibaro "Universal sensor" or "Smart implant" that can take a voltage or contact input and convert that to a Z-Wave switch activation, as well as repeating it to a floating opto output.

They are intended to be connected inline with such as security sensors, or as general inputs from switches etc.
 
gophert said:
A basic ring video doorbell is about $60. It will alert your mobile when anyone is present.
I assume your budget is less than $60?
Click to expand...

Yeah, I looked at a few of those. Seemed a possibility until I read the reviews.

£30: " Rechargeable batteries & charger cost almost as much as the doorbell. App makes this product worthless, it is not available for one of the phones in the house, when someone presses the bell the phone does not ring but sends an alert. You have to open the app before you can then respond. Alerts for motion detection arrive 5-10 minutes after the event. Removed and thrown in the junk drawer. "​
​
£180: "Doorbell installed easily with nearly full signal on existing home base 2. Homebase connected to the router via ethernet. Using with my Oneplus 6T and Fire HD 10 connected to the same router via 2.4 and 5ghz respectively. Delay of at least 5 seconds to receive motion alert or even doorbell activation after that. It's been such a big headache and caused more than a few missed deliveries, cards left etc... I have a Eufy 2C cam set up in the same location, same Homebase etc... That alerts me much sooner. I thought the cam might somehow be interfering with (or delaying) the doorbell alerting me. So I removed it from the system for a couple of days. No change with the Doorbell. Given up and gone back to using a normal wireless doorbell."​
​
​
 
rjenkinsgb said:
nd at the other extreme, some DECT phones have a "locate" button on the base unit that makes all handsets ring until cancelled
Click to expand...

Mine has a dedicated "int"(ercome) button on each handset that causes all the others to ring until cancelled or answered. It also has a "find" button on the base station that causes them all to ring.

The notion was to some how capture and replicate one of those signals.
 
AnalogKid said:
The problem is the cordless phone handset. Based on ***zero*** information, it probably has a microcontroller inside that runs all signalling and function selection.
Click to expand...

I can pick up another handset second-hand for £5 on ebay. I'm wondering about removing the circuitboard and putting it into a wall-mount box, and wire the dedicated "int"(ercome) button switch to a push botton on the front. At its simplest, it would ring the other handsets until someone kills it.

With a little more effort, hooking the mic and speaker up should be doable.

Replace the series pair of AA NiMH 850mAh batteries with something with more capacity and lower self -discharge...
 
My 20 YO vtech 2600 phone is smarter. I have the ability to global page (all handsets). After 10 rings they stop or i can page a handset separely. That page won't stop automatically.

There is encryption and everything else involved. I'm using the max of 4 handsets. I do need to replace or replace the keypad one of them
The clear all handsets method is not in the manual, but i did find it and it works.

One annoying "feature" is that the handsets are labeled "HANDSET #", where # is 1 to 4. Definatey would have liked a user defined name lie like "Base", "Dn Kit", "Liv Rm" or "Name".

The phone directory is local to the phone, not "global" and some local or just global. Entering always starts with lower letter. e.g. abcdABCD" The other way ABCDabcd" would make more sense.

All in all, it's a nicely designed phone. vtech as a company not liked so much. They replaced the charger base which was DOA initailly. Once the phone goes out of support, you can't even talk to them. I bought a phone off of ebay that doesn;t work. I replaced a charger base. The charger's have been reverse engineered and I've repaired them all.

I'm going to put one of these:


magnetic connectors on the baby monitor (glue to outside). With one button to activate, you could too.

An opto FET or OPTOMOS relay. The OPTOMOS (tiny) relay only needs 1 mA for the LED.

If you can add a handset and make it unused, then that's even better.

I think I need a photo-transistor and a resistor as well.

generally, you don;t need a short to operate the button. Sometimes even 1K will work. The isolation makes it hard to damage the handset.


nearly any of these https://bellman.com/en/product/ transmitters will work. They have an external trigger.

They use the Holtek 12e and 12E chips. **broken link removed**

It should be easy to create a receiver. This

Indestructables: https://www.instructables.com/Make-a-RF-Transmitter-and-Receiver-With-T12E-HT12/

Transmitter/Receiver modules: https://www.componentsinfo.com/fs10...-xy-mk-5v-receiver-module-explanation-pinout/

FS1000A 433MHZ RF transmitter & XY-MK-5V RF receiver module pair
Transmitter Voltage 3-5V. Receiver: 5V

design should work. It;s missing a few bits.

the Bellman transmitters are battery only,

I'd like to make a few receivers.

For me, it would be easier to put one near the bell. I even have 120VAC power nearby or can get it easily, Bellman has a doorbel transmitter that could sense the magnetics of the doorbell.

Detecting the doorbell can get tricky. ELK has a doorbell interface. You have real coil bells, chime bells and lighted doorbels at the door, so each has it;s own complication.

then there are wireless modules on Aliexpress.

I hope to be using some Linear DXS transmitters for some projects at home. They have low battery and supervision.
They are used in alarm systems.
 

Plenty there for me to read up on. Thanks.

KeepItSimpleStupid said:
Watch the number of handsets your system supports.
Click to expand...

It supports 5 handsets and we're only using 2.

Just struck me that with 2 £5 s/h handsets I can put one in a box by the front door, and attach the second to some kind of bell or horn for when I cutting grass in the garden or using power tools in the shed.
 
What's the likelyhood a circuit that uses 2x1.2V batteries would be happy with 3.2V?
 
gophert said:
Most handsets we've had use 3x 1.2v batteries.
Click to expand...
This one definitely only has 2



It's just that I can get a 6Ah LiFePO4 battery for £2.05, which is a lot cheaper than the equivalent capacity of NiMH, and ought to give several weeks of use per charge.
 
Like i said, These https://www.mouser.com/Search/Refine?Ntk=P_MarCom&Ntt=158267896 to interface with your button(s).

I do have the Belman and Symphon Home visit system.
Part #1: is the home visit alarm clock. It has a bed shaker. More like vibrating pillow. Strobes - more like flashing LEDs.
The alarm and time is easy to set and it has battery backup. Of course, it has sound. But not just a buzzer.
What I don't like is you can't set the brightness arbitrarily. It even has a "night light". A ring of LED light around the face..

Part #2. Is supposed to be part of an emergency "nurse call". A transmitter with a button would be able to activate the visist alarm and activate the pillow shaker. There is no supervision and no low battery detect. It's not a chargeable device.

Later, I plan to use a linear technology pendant transmitter that will activate this thing. The pendant transmitter has been turned into a wireless doorbell too for the back door. The other use will be water re-circulation.

I would be interested in building a Holtek receiver, so I could receive visit notifications. If anyone has time, I would chip in. I saw lots of kits in India, but not in the US.

The Visit alarm is very limited in functionality. fire/smoke, bed/baby, door/doorbell, telephone/cell phone

I'd like to mute the TV in response to the telephone, doorbell. I'd like to know which door and what phone.

Wow! The ring doorbell is that bad. Have you looked at the August lock and doorbell?

I'd like to do a more complex access control system, a video doorbell, and vertical blind controller.

Separate projects like a 6000 lumen dimmable corn-cob lamp and maybe even bed control could be on the table.

Currently, I want to get a radio (AM/FM tuner) to work.

I just finished the mounting of a nice hospital grade outlet strip on the bed which I need to write up. It will eventually include a surge supressor and a magnetic cordless phone charger base holder. The holder is aplace to put the charger base, while mom is in the wheelchair.
 
gophert said:
They are typically rated in amps, not watts.
Click to expand...
AnalogKid said:
Determine the peak current through the diode, and use one rated for at least twice that.
Click to expand...

Hm. Not sure why a seemingly simple question begets such sarcasm?

I have a circuit known to work at 2.4v and probably between 2.0v & 2.5v (min/max charge states). I'd like to replace the 2xNiMH with single 3.2v (nominal) LiFePO4 cell; and it was suggested that I use a diode to drop the voltage.

But, I do not know the current drawn by the circuit; nor do I see an simple way to measure it; given that it is likely that this battery powered DECT phone has many operating states. Ie. maximum draw may be when its ringing. Or when the speaker phone is turned on. Or it could be when it looses connection to the base station and is searching for a signal to reconnect.

Perhaps more important is the minimum power draw. If the current draw across the diode falls below some minimum value, then the 0.6v voltage drop can fall away markedly; so if the handset has a standby mode; then when it wakes up it could momentarially be presented with close to the full voltage of the LiFePO4 battery at something like 3.6v.

I guess if I had a suitable storage scope, I could try to measure that current draw across the entire range of operating modes, including waiting to see if it drops into a standby mode at some point, and then size the diode appropriately; but I don't have such a device. Nor do I have any easy way to determine the sensitivity of the components on the board to over voltage. I haven't turned up any schematics for these handsets.

In the end, i guess the safest thing to do would be to use an LDO regulator; but I'd still need some expert help in picking an appropriate device. As I've previously identified: "I know just enough about electronics to be dangerous". Ie. I have an idea of some of the things that are possible; but not the knowledge or tools to do them without assistance.
 
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