Existing intercom system

Thread Starter

miketa

Joined Feb 23, 2020
4
I am an electrician, I have a client who has an existing intercom system that currently controls two doors (door strikes, 24vac) at the same time. An outer door and an inner door.
I would like to build a circuit that with one push of the door open button on the existing intercom station, the outer door will buzz,
and with two consecutive pushes of same door open button the inner door will buzz for a preset amount of time.
In other words I need a circuit that will recognize two consecutive pushes and then it will close a relay for a short set of time (controlling the second door).
 

djsfantasi

Joined Apr 11, 2010
6,532
I can’t help with a circuit. But programmatically I’d do it as such.
  • Detect a push button
  • Set a signal or counter to indicate one press
  • Detect the button release
  • Start a timer
  • If a second press is detected, set a signal to indicate a second press
  • Increment the counter or clear the single press signal
  • When the timer expires, indicate that the data is ready...
I’ve described it specifically avoiding programming terms. In a hard-wired circuit, with the addition of a couple of transistor outputs and 555 timers, it can be made.
 

MisterBill2

Joined Jan 23, 2018
6,382
To operate both doors, here is an option. The first signal operates a timer that latches on, and one contact releases the first door. After the timer is latched, before it times out, a second pulse feeds through another contact and briefly operates the second latch. But I am thinking that DC would need to be used. But this would leave both doors unlatched for a brief time.
 

Thread Starter

miketa

Joined Feb 23, 2020
4
To operate both doors, here is an option. The first signal operates a timer that latches on, and one contact releases the first door. After the timer is latched, before it times out, a second pulse feeds through another contact and briefly operates the second latch. But I am thinking that DC would need to be used. But this would leave both doors unlatched for a brief time.
Thank you for your response. I like your idea. To build on that please note the following:
Control of the first door is already achieved by the existing intercom system. Whenever the existing door release button is pressed it will buzz the first door, I will leave that untouched. I don't mind if that first door keeps buzzing open when button is pressed.
I'm looking for a new way to control the second door. The circuit I hope to build will recognize two consecutive presses of the existing button, and then will control a relay to release the second door for an adjustable set of time. So the second door will open only with two consecutive presses while the first door will function normally.
I hope that with help from this website I can build that circuit.
 

Thread Starter

miketa

Joined Feb 23, 2020
4
I can’t help with a circuit. But programmatically I’d do it as such.
  • Detect a push button
  • Set a signal or counter to indicate one press
  • Detect the button release
  • Start a timer
  • If a second press is detected, set a signal to indicate a second press
  • Increment the counter or clear the single press signal
  • When the timer expires, indicate that the data is ready...
I’ve described it specifically avoiding programming terms. In a hard-wired circuit, with the addition of a couple of transistor outputs and 555 timers, it can be made.
Thank you for your reply. I'm looking for help to build that circuit. But please note the following:
Thank you for your response. I like your idea. To build on that please note the following:
Control of the first door is already achieved by the existing intercom system. Whenever the existing door release button is pressed it will buzz the first door, I will leave that untouched. I don't mind if that first door keeps buzzing open when button is pressed.
I'm looking for a new way to control the second door. The circuit I hope to build will recognize two consecutive presses of the existing button, and then will control a relay to release the second door for an adjustable set of time. So the second door will open only with two consecutive presses while the first door will function normally.
I hope that with help from this website I can build that circuit.
 
Double presses are wierd because you have to time-out to reset the timer.
Switches bounce. Meaning when they are pressed, circuits can think they are pushed a variable number of times.
You do have to do a little reverse-engineering to tap into the existing button.
Your only building one of these?

I don;t like the hardware method, but you will need some "glue logic" to interface to the intercom.

take a look at the Idec smart relay: http://us.idec.com/Catalog/ProductFamily.aspx?FamilyName=Programmable_Relays
and
the Siemens LOGO https://new.siemens.com/global/en/products/automation/systems/industrial/plc/logo.html

the nice part is that you can simulate without buying the software or hardware.

Also take a look at www.picaxe.com

What is the current strategy if there is no power?

maybe it is do-able with hardware only.

let's say you have a de-bounced contact which means a clean edge. This probably means 10-100 mS. then you have a time-out of say 3s. Let's say the button generates a rising edge when pushed.

A push then starts timer A for 3s and is non-retriggerable and another, timer B, that will generate a pulse of x ms which is re-trigerable. That x ms pulse counts by 1. When timer B times out, you examine the counter.

if 0 then nopulses
if 1, pulse to the one push door
if 2, then a pulse to the two pulse door
if 3, reset counter

two flip flops could count 0-3.

On the falling edge of any door, reset the counter.

Analog devices Timerblox might be easier to work with, but it requires a 5V power supply. 555 timers are flakey.

You also need a power on reset for the counter.

So, in essence the pulse to open any door occurs after say 3s. Maybe less.

A Long and short press might be better and maybe even easier.
 

MisterBill2

Joined Jan 23, 2018
6,382
One of my moost popular products used a "Tri-Flop", where the first pulse triggered the first output, and the second pulse, within 100 milliseconds, triggered the second output, and then after about 300 milliseconds it would always reset both outputs to zero. And one pulse, that triggered just the first output, would also reset to zero, after about 400 milliseconds.
The time delay would need to be adjusted for manual operation, but the circuit could be the same. That circuit uses a CD4013 FF with resistors and an RC time constant from the "Q" outputs to drive the Reset inputs of the two sections. It ALWAYS defaults to both outputs off at first power on. And it has been in use for almost 20 years. Simple, reliable, and cheap.
 

Thread Starter

miketa

Joined Feb 23, 2020
4
Double presses are wierd because you have to time-out to reset the timer.
Switches bounce. Meaning when they are pressed, circuits can think they are pushed a variable number of times.
You do have to do a little reverse-engineering to tap into the existing button.
Your only building one of these?

I don;t like the hardware method, but you will need some "glue logic" to interface to the intercom.

take a look at the Idec smart relay: http://us.idec.com/Catalog/ProductFamily.aspx?FamilyName=Programmable_Relays
and
the Siemens LOGO https://new.siemens.com/global/en/products/automation/systems/industrial/plc/logo.html

the nice part is that you can simulate without buying the software or hardware.

Also take a look at www.picaxe.com

What is the current strategy if there is no power?

maybe it is do-able with hardware only.

let's say you have a de-bounced contact which means a clean edge. This probably means 10-100 mS. then you have a time-out of say 3s. Let's say the button generates a rising edge when pushed.

A push then starts timer A for 3s and is non-retriggerable and another, timer B, that will generate a pulse of x ms which is re-trigerable. That x ms pulse counts by 1. When timer B times out, you examine the counter.

if 0 then nopulses
if 1, pulse to the one push door
if 2, then a pulse to the two pulse door
if 3, reset counter

two flip flops could count 0-3.

On the falling edge of any door, reset the counter.

Analog devices Timerblox might be easier to work with, but it requires a 5V power supply. 555 timers are flakey.

You also need a power on reset for the counter.

So, in essence the pulse to open any door occurs after say 3s. Maybe less.

A Long and short press might be better and maybe even easier.
Thanks for your reply, it's going to take me some time to digest the info you sent, I'm an electrician, I don't have the electronics background.
I think there is real potential to sell this circuit as an add on to existing intercom systems (mainly to apartment buildings with older intercom systems).
I think using the output signal from the existing intercom to the existing door strike (24vac), as the signal to monitor for the two pushes to control the second door. I think most electronic bounces are short in duration, so we should only consider pushes of significant duration, and that will eliminate the phantom pushes.
 
I/O modules are used to interface to PLC's. e.g. http://www.grayhill.com/assets/1/7/IO-Intro.pdf

Info on contact bouncing: https://www.allaboutcircuits.com/textbook/digital/chpt-4/contact-bounce/

I think most electronic bounces are short in duration, so we should only consider pushes of significant duration, and that will eliminate the phantom pushes.
Those short pulses are picked up and counted by electronics. Certain circuits need edges to work. See Schmidt trigger: http://www.ti.com/lit/an/scea046/scea046.pdf
 

MisterBill2

Joined Jan 23, 2018
6,382
I will consider how to slow a "tri-flop" circuit so that it can work with a pushbutton instead of a computer. That should be possible. I know that it can be done with two time delay relay modules, but that may be expensive. And also, I know that the door release devices get an AC signal, because a DC signal should not buzz like that. And the IC version must have DC for the IC.
 

djsfantasi

Joined Apr 11, 2010
6,532
Thanks for your reply, it's going to take me some time to digest the info you sent, I'm an electrician, I don't have the electronics background.
I think there is real potential to sell this circuit as an add on to existing intercom systems (mainly to apartment buildings with older intercom systems).
I think using the output signal from the existing intercom to the existing door strike (24vac), as the signal to monitor for the two pushes to control the second door. I think most electronic bounces are short in duration, so we should only consider pushes of significant duration, and that will eliminate the phantom pushes.
Have you considered something that instead of requiring a double press, determines the output in length of press? Holding the button down for 100ms enables option 1, 250ms enables option 2 and anything over 400 ms resets the system...
 

MisterBill2

Joined Jan 23, 2018
6,382
Have you considered something that instead of requiring a double press, determines the output in length of press? Holding the button down for 100ms enables option 1, 250ms enables option 2 and anything over 400 ms resets the system...
An automatic timer reset is the only thing that makes sense. Keeping a door release buzzer activated can burn it out.
 

djsfantasi

Joined Apr 11, 2010
6,532
An automatic timer reset is the only thing that makes sense. Keeping a door release buzzer activated can burn it out.
Good point. However, in this scheme no action is taken until the button is released. Then, one of several outputs is set based on the length of the press. Can be done in hardware with a slow counter (4Hz) triggered by a button press and latched by a button release.
 

MisterBill2

Joined Jan 23, 2018
6,382
The concept of pressing the button twice is intuitive, while pressing it for different lengths of time is not. In addition, it would be far more complex to implement, sice it would need both a pulse generator and a counter. Those would need to be designed and built, while time delay relays are quite available in a number of different sizes and ratings, from at least a dozen different manufacturers. AND their functioning is well understood by most electricians.
 
Have a Samsung remote control.

"UP" - Volume UP
"Toward remote" - short press - mute
"toward remote" long press" - menu
"DOWN" - volume down

Car radio - Push and hold until settings menu appears

Computer
Click and double-click

I don't think the push and hold would be too bad IF, you held until the strike clicked. It would be bad if you had to wait until a timeout.
 

MisterBill2

Joined Jan 23, 2018
6,382
The first push would immediately release the first door and immediately latch the first timer relay Until that one times out, the next push releases the second door. Once the first timer times out it all reverts back to ready. And that time out can be as few seconds as desired.
 

djsfantasi

Joined Apr 11, 2010
6,532
The concept of pressing the button twice is intuitive, while pressing it for different lengths of time is not. In addition, it would be far more complex to implement, sice it would need both a pulse generator and a counter. Those would need to be designed and built, while time delay relays are quite available in a number of different sizes and ratings, from at least a dozen different manufacturers. AND their functioning is well understood by most electricians.
Ok, I can’t disagree with you.

However, implementing different functions based on the time pressed is not unknown. I’ve built several successful devices that are controlled that way.

Tomat-oh, Tom-ah-to... None of the users of my device found it difficult to press once versus double pressing. So what you think is intuitive may not be intuitive to someone else.

I did not implement it the way I described. I used a microprocessor and the technique is SIMPLER to implement with a μP.
 

MisterBill2

Joined Jan 23, 2018
6,382
After purchasing the arduino, the power supply for it, the programming cable, and a pair of interface relays to handle the 24 volt AC signal to the door latches, and the interface between the 24 volt signal and the digital input, the whole package still needs a suitable enclosure and a mains connection for the wiring. Building a package to last 20 years unattended in a building is a lot different from assembling a hobby project on a desktop.
 

djsfantasi

Joined Apr 11, 2010
6,532
Me thinks thou doth protest too much. A little exaggeration perhaps?

Arduino’s, power supplies and programming cables are often bundled. Calling out the individual components is misleading.

Besides, once you have made more than one Arduino project, you’ll likely have extra programming cables. There is nothing special about an Arduino programming cable; it is a standard USB-B to microUSB cable.

You’ll need a power supply no matter what. So calling out the need for an “Arduino” PS is disingenuous.
 
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