Simple EOL. DOEL alarm zone input detector?

[asrock70]

I am looking for some simple solution to evaluate the status of the alarm line
A typical alarm line connection is Double End Of Line
possible states
No Alarm R=R1+RL
Alarm R=R1+R2+RL
Sabotage R=High resistance (may be over 7k Ohm)
Sabotage R= short circuit (may be under 100 Ohm)
I'm looking for some funny solution that can be connected to a Raspberry, for example.
Then I thought of using a module with AD1115 I2C 4 input 16 bit ADC for $2. The main thing that bothers me here is the 4 inputs, I need 6 of them
The second option was some STM32 MCU and its ADC. Unfortunately, I have no experience with the reliability of I2C programmed as a Slave
Thank you.

 

[KlausST]

Hi,

I don´t understand the expression "Double End Of Line"
All Rs are defined, except RL. What is it? What value (range) does it have.

What does "funny" mean in this regard?

Why using external ADC? Doesn´t the Raspberry provide analog inputs?

AD1115 provides 4 selectable addresses ... so you may use 4 x AD1115 on one I2C bus.
You talk about a module --> provide a link to it´s datasheet.

What does "reliability" mean here?

Klaus

added:
This application surely does not need a 16 bit ADC. 8 bits will do.

 

[betwixt]

All you need to do is look for a change in resistance in the chain of sensors. Easiest way to do that is to ground one end of the loop, add a resistor to a stable power source (for example the 5V feeding the Pi) at the other end of the loop and measure the voltage at that point. Any change in resistance will result in a change in voltage and you can measure that with no other components at all, just use the Pi analog input. With some care in selecting resistances at the sensors, you can even tell which alarm was operated.

Brian.

 

[asrock70]

Hi,

I don´t understand the expression "Double End Of Line"
All Rs are defined, except RL. What is it? What value (range) does it have.

What does "funny" mean in this regard?

Why using external ADC? Doesn´t the Raspberry provide analog inputs?

AD1115 provides 4 selectable addresses ... so you may use 4 x AD1115 on one I2C bus.
You talk about a module --> provide a link to it´s datasheet.

What does "reliability" mean here?

Klaus

added:
This application surely does not need a 16 bit ADC. 8 bits will do.

DOEL is an established term used in the field of alarm control panels
NO, NC (Normal Open, Normal Close)
It distinguishes only two states, it is possible to overcome them by shorting or disconnecting the line and therefore it must not be used for a safety control panel
EOL (End Of Line) A resistor R1 is added to the line, three states of the line can be distinguished.
DEOL (Double End Of Line) As EOL, but added resistance R2 at each sensor (shorted in normal state by relay NC) and thus 4 states can be distinguished
RL is the resistance of wires and contacts and NC relay contacts on the line, usually up to 10 ohms.

Raspberry has some ADC inputs, but not enough of them and most importantly, I'm not sure it's reasonable to entrust it directly to something with such a complicated SW.I have had the Alard DSC 2550 at home for about 30 years and it works without a single malfunction or jam. Even simple modems with Linux, which is simpler than the one in raspberry, have already stuck at least once.I am aiming for a solution that will be basically as reliable as the DSC2550, but will allow me more options, where my basic requirement is communication and the Telegram application.
The first option is to simply connect the DSC2550 with a raspberry or replace the DCS with something.
Yes I know I can use 4x AD1115, but it means 4x IRQ output, but an is it a solution, I don't know how to say it.
I just remember the time when a 16-bit ADC cost as much as a car and something makes me want to use 4 pcs for some stupidity

--- Updated Jun 13, 2024 ---

I thought a bit about using a processor, perhaps STM32G0, and programming it as a Slave on I2C, but from what we've read, it's not exactly easy for an MCU on I2C to work as reliably as HW I2C. Does anyone have practical experience with this?

 

[KlausST]

DOEL is an established term used in the field of alarm control panels

Using application specific terminology reduces the response. This may be a good idea if you just want "alarm designers" to respond.
Your application is a rather basic "resistor divider problem".

Raspberry has some ADC inputs, but not enough of them

Just use a simple MUX to switch between channels.

I'm not sure it's reasonable to entrust it directly to something with such a complicated SW

Objectively .. there is nothing complicated at all. Neither complex, nor timing related.
The processing power of an RPi should be sufficent to easily handle 10,000 of such alarm channels.

If they "stuck", then there is something done not correctly. A correct design starts with specifying the requirements according accuracy, timing, signal flow ...
If designed properly it will run reliably.
If not designed properly .. it does not matter whether it´s HW, SW or a mixture ... it is always prone for failure.

I know I can use 4x AD1115, but it means 4x IRQ output,

I see no problem with 4 IRQs. But you don´t need to use them. Again: it´s a question of proper requirements and design.

it's not exactly easy for an MCU on I2C to work as reliably as HW I2C.

The same as above. The I2C periferal on any microcontroller (even the tinyest ones) work reliably. But a poorly designed software will make the system unreliable.
You are the designer .. it´s in your hands.

Klaus