(Solved) Reading a smoke detector

I've been reading up on a starters electronics book. For kicks and giggles I decided my first experiment regarding circuit understanding should be a fire alarm. I found the total resistance when the alarm is not active is around 595 ohms. The volt input is 9V, and I believe the current should be around .015 when the alarm is not active.

I thought I could read this with the arduino as an analog so I hooked the positive of the battery to the alarm, and the negative side I attached to A1..

For some reason it isn't working though. When I unattached the 9V battery, and hook the positive to the 5V from the Arduino and the negative to A1 it beeps, and if I do the same using the positive and negative of the battery it beeps. Why won't it beep when I use the positive of the battery, and the ground from the arduino?

How do I get a reading the arduino can register directly from the alarm, without using a microphone speaker based system to detect the noise?

I don't like the sound of this. Are you sure you didn't connect 9V to the arduino ? Please post a link for the alarm and a photo of a hand drawn schematic of your circuit. Do you know how to draw a schematic ? Have you used an arduino analog input before ? Why are you using the analog input ? Are you sure the alarm output isn't simply a high or a low signal ? What makes you think it is a varying analog signal ? On what are you basing that assumption ? Do you have any documentation ? I don't see anything in your post that suggests you have taken any measurements with a Digital Multimeter. Have you ? When you say "fire alarm" do you by any chance mean "smoke detector" ? (that is not a fire alarm. It is a smoke detector. A "fire alarm" uses a totally different kind of sensor.)

Do you have any electronics experience ?

I've been reading up on a starters electronics book

This comment would be a "NO", correct ? Does that mean you don't know Ohm's Law ?

I don't like the sound of this. Are you sure you didn't connect 9V to the arduino ?

Yes, on the 9V battery, I attached the smaller rounder battery side to the alarm. The other part of the alarm I first attached to A1, then when that didn't work I tried to attach it to the ground of the arduino.

Please post a link for the alarm and a photo of a hand drawn schematic of your circuit.

This thing is ancient. It came with the house, which is very old. It is made by black and decker but I can't seem to find any links that reference this model. This is probably because they quit making it before the internet became popular. - How do you post pictures on this site? It has this radioactive black ball looking thing in it.

Do you know how to draw a schematic ?

I have seen the first three videos on circuits from khanacademy.org But.... that's about the limits of my experience regarding schematics.

Have you used an arduino analog input before ?

Yes, a few times.

Why are you using the analog input ?

If I used digital it would only read on or off. There is current passing through the alarm even when the alarm isn't active. Fast forward to mark 5:40 into this youtube video

Are you sure the alarm output isn't simply a high or a low signal ? What makes you think it is a varying analog signal ? On what are you basing that assumption ? Do you have any documentation ?

I am not sure of anything regarding this experiment.

I don't see anything in your post that suggests you have taken any measurements with a Digital Multimeter. Have you ?

I have. I have a GREENLEE DM-40 multimeter.

When you say "fire alarm" do you by any chance mean "smoke detector" ? (that is not a fire alarm. It is a smoke detector. A "fire alarm" uses a totally different kind of sensor.)

It isn't a M2Q shield if that's what you are asking. It has the radioactive smoke detector thing. It doesn't detect methane and other gases like the arduino based smoke sensor shields do.

Do you have any electronics experience ?

Very little. I bought the book Getting Started in Electronics and am now on page 32. I wanted to do some hands on experiments to make sure I was comprehending everything accurately before continuing on.

Does that mean you don't know Ohm's Law ?

Voltage = Current times Resistance

That pretty much sums up what I know about Mr. Ohm at the moment. But I'm eager to learn more!

Ok. Here is what I think.

1- With your limited experience you shouldn't connect ANYTHING from the smoke alarm to your arduino unless you want to destroy it. 2.- When attempting to interface unknown (meaning no schematic) electronics to a uC, it is SOP to: A- Draw a schematic. (since that seems to be out of the question , PLAN B B- Make a wiring list.

Label the columns like this: UUT (Unit Under Test , ie fire alarm) Arduino BATT-9V OUTPUTS GND---DMM BLK LEAD ---NOT CONNECTED)-----NEG POS BATT TERM--------------------------------------POS OUTPUT (Dig/Anal/?)----- DMM RED LEAD

3- Do you have the resistor connected ? 4- Have you measure the RESISTANCE across the alarm terminals ? (YES, 595 ohms) 5- Have measured the Voltage across the alarm terminals ? (no info) 6- Have you measure the current across the alarm terminals ? (you said it is 0.015 (what A ?)if so it's i5 mA.)

(DO NOT DO THIS UNTIL YOU DO #4 &

5 AND REPORT BACK YOUR OBSERVATIONS !)

7- IS THIS AN ALARM (a black box that does nothing more than detect the handle pull) OR is a DETECTOR ?

DO NOT UNDER ANY CIRCUMSTANCE CONNECT YOUR ARDUINO ANY MORE TO THIS THING ! You are not ready for that yet.

Report back with your SITREP (Milspeak for SITUATION REPORT ) after performing the above. Good luck Mr. Phelps....

FYI, THIS:

GND---DMM BLK LEAD ---NOT CONNECTED)-----NEG

means the battery neg term connected to alarm neg term . Arduino out of the circuit.

It just occurred to me you haven't told us how many connections the alarm has to the 'outside world' ie : OUTPUTS.

3- Do you have the resistor connected ?

Besides all the resistors that are in the alarm already, No I didn’t do that.

4- Have you measure the RESISTANCE across the alarm terminals ?

I took out the 9V battery and switched the volt meter to measure resistance and put the prongs to the place where the battery is suppose to go. The reading I got was 595 so I think the total resistance (when alarm is not activated) is 595 ohms.

6- Have you measure the current across the alarm terminals ? (DO NOT DO THIS UNTIL YOU DO #4 &
#5 AND REPORT BACK YOUR OBSERVATIONS !)

Strangely enough, that never came across my mind. As you suggest, I will wait until farther instructions before attempting this.

7- IS THIS AN ALARM (a black box that does nothing more than detect the handle pull) OR is a DETECTOR ?

I downloaded four pictures that show whatever this device is. (Fire alarm, or smoke detector) as well as setup I have going. - In the picture, the ground to Arduino is connected to Arduino Ground, but originally it was connected to A1 in hopes of reading the current and to be able to detect if alarm was active or not.

UUT ( fire alarm) (in picture attachment)
Arduino BATT-9V
INPUTS to Alarm
Power - Connect to 9V battery

OUTPUT (Ground connected to Arduino Ground (eventually would like to go back to A1 for readings) (Analog)

BackOfAlarm.jpg

FrontOfAlarm.jpg

The video shows an alarm panel with wires (two) going to the other hardware. Where are those terminals ? That's what we need to know first. Your calculations for the alarm operating current are correct , but that's not what we are interested in. We need to know : Where is the resistor mentioned in the video ? Are there any terminals such as the ones mentioned in the video ? What is the resistance across THOSE terminals ? It would appear from the video , the alarm has TWO input terminals and SOME unknown number of terminals that signal the fire dept. Your mission is to : 1- identify the INPUT terminals (not the battery terminals) 2- identify the OUTPUT terminals (how does it signal the fire dept ?) 3- Verify that the audio alarm siren/horn/bell is built into the device and not external. 4- If possible, ascertain if this alarm is even remotely similar to the one in the video. 5- Identify any indicator LEDS/LIGHTS 6- Locate the smoke sensor. 7- Post a photo of the case (box) , if you have it.

The video shows an alarm panel with wires (two) going to the other hardware. Where are those terminals ?

The video was just a reference that I watched before hand that shows current is always going through the alarm even when not active. Therefore a digital reading wouldn't work if I wanted to figure out if the alarm was in active state, or alarm state.

Where is the resistor mentioned in the video ?

I found several resistors in the alarm, but I don't know how to identify what they do. Some may be used if the alarm detects a threat, some may be used if the user manually test the alarm, I just don't know which resistor is "the resistor" you are asking for.

Are there any terminals such as the ones mentioned in the video ?

No, This is all I have. This alarm wasn't designed to work with terminals anyway.

1- identify the INPUT terminals (not the battery terminals)

I thought about taking it apart farther, but the radio active warning made me think twice about it. I didn't want my first experiment to potentially cause me to not be able to have kids one day.

2- identify the OUTPUT terminals (how does it signal the fire dept ?)

It doesn't notify emergency service providers. It will broadcast a very loud audio warning when it detects a threat. That's all it does.

3- Verify that the audio alarm siren/horn/bell is built into the device and not external.

The speaker is attached by wires. You can kind of see it in the previous pictures, but I stuffed cotton balls in it and taped it up using medical tape to damping the sound it made when the batteries were taken out/put in.

5- Identify any indicator LEDS/LIGHTS

I don't know if Led's were even out yet when this alarm was designed. There are no lights or LEDS in it.

6- Locate the smoke sensor.

It's the black thing in the middle with the Radio-active symbol.

7- Post a photo of the case (box) , if you have it.

I posted the four pictures in the previous post that showed this.

MISSION ABORT ! There is nothing you can do with alarm short of using the speaker wires to drive an opto isolator that sends a digital signal to the arduino. This device has no output other than the speaker. Did you identify the smoke detector ? What is the point of sending a signal to the arduino if the alarm speaker is blaring ? Give it up and find another project. Just out of curiosity, have you tested it by blowing cigarette smoke into the sensor ? (or holding it above a burning piece of paper ?)

Did you identify the smoke
detector ?

Yes, I posted this two post ago along with 3 other pictures, but will post it again. See attachment. The black circular thing with the radio-active symbol. To my understanding, there is a high likely hood that that thing is what detects the smoke.

What is the point of sending a signal to the arduino if the alarm speaker is blaring ?

The only point is to experiment and to make sure I understand the concepts I am reading about regarding circuits. Most electronics today are extremely small and aren’t ideal for beginners like myself to start experimenting with. This alarm was made at least 30 years ago, and you can actually see all the pieces inside without a magnifying glass.

Regardless of what Mr. Moore’s Law says, for beginners trying to learn, simplifier is better.

(or holding it above a burning piece of paper ?)

The test button works, I have not tried burning a piece of paper, but I can do that tomorrow. (Room mates would kill me if I did that tonight, it’s midnight here)

MISSION ABORT !

I would like to continue this experiment and get the arduino to comprehend the alarm is going off. I believe understanding simple circuit concepts like this will help me in the long run. If it makes you feel better, I could get the arduino to comprehend there is a potential environmental threat, and to turn the Christmas tree lights off if the alarm goes off. It is Christmas time, and people do insist on hanging paper coffee filter decorations and other extremely flammable decorations on trees with electrical lights, and they leave the lights on all night while they sleep unsupervised. If you want a worse case scenario, they could be awaken to a fire alarm going off, and in panic they attempt to throw a bucket of water on the fire. Without the arduino, this could result in electrocution on Christmas because the arduino didn’t turn off the Christmas tree lights when the fire started.

In reality, a fire extinguisher would likely be used instead of a bucket of water. fire extinguisher aren’t likely to result in electrocution, but if you need a scenario on why it would be useful, there you have it.

FrontOfAlarm.jpg

As interesting as this project seems, I'd be more interested to see pix of the coffee filter paper decorations, which I've never had the privilege to see before. Sounds vile. (Are they unused, used but emptied, or used but full of coffee grounds?)

As interesting as this project seems, I'd be more interested to see pix of the coffee filter paper decorations, which I've never had the privilege to see before. Sounds vile. (Are they unused, used but emptied, or used but full of coffee grounds?)

This is unusual. I take it you are not from America? Maybe it's a local thing. People take unused coffee filters and fold them up to make a triangle. (fold the coffee filter in half, then fold it in half again, then maybe half one more time) then cut pieces out and unfold it. It makes a snow flake looking decoration. Kids love to make them, parents love to put things their kids make on trees.

Google "opto coupler " or "opto isolator" with the word arduino in front of it and the word "circuit" after it. Have fun. All you need is one resistor on the input side . I" ll let you see if you can figure out what to do with the output side.

Henceforth ALL (or at least 99.99%) of your Google searches will contain the following KEYWORDS:

ARDUINO [blank] CIRCUIT CODE EXAMPLE

Where | [blank] is replaced with the device or subject of interest

In this case , your search is for opto isolators (AKA OPTOCOUPLERS),

thus , the search KEY PHRASE is:

"ARDUINO opto isolator CIRCUIT CODE EXAMPLE " (without the "")

Henceforth you will NOT post a new topic on the forum until you have:

1- done a GOOGLE SEARCH 2- done a search for any calculations or formulas that might be relevant to your topic 3- done a search for example code that might be relevant to your topic 4- drawn a schematic of your circuit. 5- If you don't know what it would look like do a Google search for "blank" SCHEMATIC 6- Made a list of relevant questions to ask in your post 7- composed a project SUMMARY/INTRODUCTION 8- compiled a list of LINKS (for the hardware you are interfacing) , copy and pasted into a Notepad file and saved under the topic name To Post a LINK; 1. Click on the "chain" symbol between the computer monitor symbol and the envelope. 2. Paste the URL (link) into the FIRST box you are promted with, click OK. 3. Type in a label for the link (ie: "these", "here" , or the name of the thing, click OK.

9- compose your post in Notepad and reread it several times to look for omissions/mistakes 10- Learn how to read/use datasheets. Always post link to them when asking questions about the thing/ic/device in question. Google the parameter names if you don't know what they mean. (this is the 0.01% where you DON'T use the prefix "arduino" and the suffix "circuit")

Did I miss anything (ANYBODY .? ...ANYBODY ....?)

And learn how to draw a schematic so you can post a photo of your schematics. Google schematic tutorial or something. That is VERY IMPORTANT. If you do NOT learn how to draw a schematic , you will essentially be an electronics cripple. You will have a handicap that will always slow you down and make it next to impossible to communicate with the forum members who reply to your post. Make that your TOP priority.

FYI, There is a special HELL reserved for people who don't read datasheets. It is a place where nothing works and everything smokes when you turn the power on. I can't count the number of posts we've seen on the forum because people didn't read the datasheets.

Also, you might want to read the specs for the arduino UNO on the home page to familiarize yourself with the voltage limitations etc.

Also, you should do the examples that come with the IDE. When you click Tools, there should be an Examples menu that allows you to select examples.

Good luck

Well it's a relief that they use unused ones, although the greens might advocate re-cycling?

If you get the alarm and the opto interface workiing we can talk about turning the christmas tree lights off.

Thanks for the advice. I love homework, it gives you a solid direction to go in.

2- done a search for any calculations or formulas that might be relevant to your topic

I know Mr. Ohms law. I can’t think of anything other formula that would be relevant to this project to search for.

3- done a search for example code that might be relevant to your topic

This was the best I could find that didn’t use a MQ2 shield that was actually designed to be an accessory of arduino.

int analogPin = 0;
int ledPIN = 13;
int val = 0;
 
void setup()
{
  pinMode( ledPIN, OUTPUT);
  Serial.begin(9600);
}
 
void loop()
{
  val = analogRead(analogPin);
  Serial.println(val);
  if( val > 50 ) digitalWrite( ledPIN, HIGH);
  else digitalWrite( ledPIN, LOW );
  delay(500);
}

To address number 4 I found this link and this 3 minute youtube video that shows the schematics on how the radioactive detector works.

6- Made a list of relevant questions to ask in your post

  1. So I should probably purchase a 4N35 optocoupler to proceed with this project?

  2. The speaker hookup on the fire alarm I have has three wires leading to it. I believe it is a magnet speaker. I posted a schematic layout I drew of the connection setup. In this setup, does the green wire need to go to the arduino at all?

  3. Would it be possible to measure the current by hooking the ground of the alarm (battery port) to the arduino A1 to detect if the alarm was active/not active? This is shown in an attachment in a previous post on this thread, but was never really answered.

Also, you might want to read the specs for the arduino UNO on the home page to familiarize yourself
with the voltage limitations etc.

Arduino to my understanding can handle 5V. I recently purchased This 9V battery power supply but it has not yet arrived. I am curious if hooking this up would be bad because I think it would power the arduino with 9V. ?

I will start right away with the data sheet/ schematic tutorials.

Have you ever seen a speaker with 3 wires ? Think about it. If you put your meter on RESISTANCE and measure across speaker terminals what will it tell you ? Are you telling me you haven't measured the speaker resistance and that's why you don't know which two of the three are the speaker wires ? Is it possible the green wire is the earth ground for the speaker case ? Did you measure across the two non-green wires for resistance (with one lead disconnected from the alarm) and for voltage with the speaker alarm tone ON ? You don't care about current because thanks to Mr. Ohm YOU decide the current when you pick your resistor value for the opto. Thank you Mr. Ohm. May I have another ?

Did you measure across the two non-green wires for resistance (with one lead
disconnected from the alarm)

To get one lead disconnected from the alarm, I would have to cut the wire. I don’t really know how to solder yet. So no, I didn’t do that. I do have some super glue so if you want me to cut the wire to take the reading, I could probably glue it back on.

The red wire is positive and the black is negative. When the speaker is active I get a reading of about .32 volts

I included in the attachment a schematic I drew that represents a basic fire alarm, based on what I was able to find on youTube videos.

Where do I go from here?

Leave the wire connected and measure the speaker resistance. Trace the grn wire to see if you can find out where it goes.

I see your learning to draw schematics. It’s a little rough but it’s a start. What is “this” component ?
(see attached)

I do have some super glue so if you want me to cut the wire to take the reading, I could probably glue it back on.

Is this supposed to be a joke ? Does superglue conduct electricity ?