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how to connect a smoke detector with PIC16F877A

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maxster03

New Member
Hi there,

i want to ask you how can i connect a smoke detector who is giving me an output voltage of 2.20V to 2.50V (which is not constant) when it detect smoke and 0V when it doesn't detect smoke.

for the PIC16F877A, i need a constant voltage of either 0V or 5V

Can anyone help me with this problem, PLEASE !
 

Pommie

Well-Known Member
Most Helpful Member
If the output from the smoke detector normally drives the sounder then it is probably a square wave of amplitude 5V that your meter is showing as 2.5 as it's only on half the time.

If it isn't a square wave and is a constant 2.5V then a transistor will do the job.
**broken link removed**
The signal to the pic will be inverted but that can be fixed in software.

Mike.
 

maxster03

New Member
yeah i am taking the output voltage of the buzzer, the thing i don't want the buzzer to go off when it detects the smoke, only to give input the PIC

the problem is i can't test the sensor inside the laboratory because of the smoke detectors in the lab. so i checked tht outside the laboratory with a digital voltmeter so i am not sure if its a square wave or not, but the voltage was not constant,

plus the buzzer have three wires, one is black, the second one is red and the third one is white, so i believe the black is for ground, red for positive and the white is for the signal, where should i measure the voltage across ground and positive supply or the signal ???
 

alexyee

New Member
hi there, i doing a home security system project . Require modify the Smoke alarm model ss-168 but dont know how could i modify it . Could any expert give me a guide on how to modify the smoke alarm circuit to connect with pic16F877a
 

Reloadron

Well-Known Member
Most Helpful Member
The smoke detector you mention does have an RF option allowing it to send a signal to other like detectors and trigger them. Any units with that option could likely be hacked. The small circuit that Pommie posted could also be used taking the signal from the sounder. However, if this is a square wave you would add maybe a flip flop to get a steady state on or off signal of 5 volts to feed the PIC digital input. The trick is knowing what you have for a signal. Personally I would look for a smoke detector that has the outputs you need. This because you don't want to hack a detector which your life may depend on.

Ron
 

alexyee

New Member
I plan to modify the circuit as part of my home security project . Instead of the smoke detector (ionization chamber) detected the smoke and sound the buzzer/alarm . I would want the smoke detector send signal of 5v on/off to pic and pic will activate the buzzer. So if i would like to use the readily build sensor how could i modify it to suit my usage or is there any where to construct a circuit by detecting the smoke with the ionization chamber sensor .
 
Last edited:

Reloadron

Well-Known Member
Most Helpful Member
You need to see what signal goes to the sounder, I am guessing a square wave as was mentioned. That signal would be connected to a transistor circuit like Pommie posted and the if a square wave it could be connected to a D flip flop to give a state change. Additionally another method might be to open the smoke detector and using a voltmeter probe for a voltage change (the signal that triggers a square wave out) and then it can be worked from there. The trick is finding a voltage that changes a steady logic state when smoke is detected. So yes, there are ways to do it, problem is I don't have your smoke detector sitting here with the circuit in front of me so the best I can come up with is generic suggestions.

Ron
 

alexyee

New Member
I check the voltage of the buzzer and the ionization chamber . It is not constant which fall below 2.5v.
This is the smoke alarm interrior,
https://i281.photobucket.com/albums/kk239/alexyee90/DSC01246.jpg
https://i281.photobucket.com/albums/kk239/alexyee90/DSC01264.jpg

And there are some small resistor with label code :
R7 = 228
R6 = 104
R1 = 104
R3 = 102

R2 = 755

R13 = 5R1

R5 = 155
R4 = 683

R0 = 0
R12 = 102
R8 = 472
R16 = 472
R14 = 102

R11474

Doen't know wht all the about .
Hope these info able to help out in modify the circuit .
 

colin55

Well-Known Member
Talking Electronics detector circuit takes current taken by the smoke detector to trigger the alarm.
 

alexyee

New Member
Colin55 , yup the problem is i dont know want where to connect solder/ connect the jumper wire so that it can send signal to my pic . thx
 

colin55

Well-Known Member
Yup, my circuit is cleverer than that. It monitors the supply current and triggers after a short period of time. This neglects the effect of self-testing and beeping that occurs every minute.
 

alexyee

New Member
Can you post ur circuit here so i can be use it as my smoke detector in case my smoke detector problem dont solve, thx .
 
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