Need Help

[maxster03]

Hi Everyone !

I am working on a project in which i have to connect a Smoke detector with a PIC16F877, i don't want the smoke detector buzzer to sound but i want it to send the input signal to the PIC when it detects smoke, i have tested the smoke detector and it is giving a 5V to -5V square wave, the sound buzzer has 3 wires red, black and white. i calculated the volatge across red and black wires.

Can someone tell me how I connect the smoke detector (which wire) with the PIC.

Thank you so much to everyone who replies in Advance

Murtaza

[BobK]

Hi Maxster,

Measure the voltage between the Black and white wires in the normal state, then measure the voltage across those same wires in an alarm state. If there is more than 2 volts IN ALARM then you could connect the LED side of an optoisolator to these points then disable the buzzer. Then connect the phototransistor side of the optoisolator to your external circuitry to do whatever it is you need to activate.

PLEASE REMEMBER THIS SHOULD NOT BE USED IN ANYWAY SHAPE OR FORM AS A LIFESAFETY DEVICE. THIS IS ONLY FOR EDUCATIONAL PURPOSES.

Now if you can get your hands on a "systems oriented" type of 4 wire smoke detector then you can supply 12 or 24 volts DC to the detector and you have a built-in set of Normally Open relay contacts that you can use to trigger whatever it is you are trying to activate.

I have not included and diagrams only because I do not know your level of knowledge. Let me know.

Hope this helps you out.

BobK

[maxster03]

Thank you so much for your reply
well i am a student and i am doing my final year project on home alarm system.
i haven't used Smoke detectors before, so i am not quite sure what to do

when you say i should measure the voltage when in its OFF and ON state, do you mean i should take it with a voltmeter or oscilloscope, i think they should be same but they are giving me different values, and please can you include the diagrams which your saying, that would be help me out.

thanks again for your help
really appreciate it

[Archangel]

Hi maxster03,
You could use the buzzers 10v square wave signal through a diode bridge and send that power through a 78L05 regulator directly to an input on the PIC.

[BobK]

Hi Maxster03,

I have made an assumption that you are using a battery operated smoke alarm. We in the alarm profession call a 110vac or battery operated detector a smoke alarm. One that is made for alarm systems integration (wired in) is called a smoke detector.

Anyhow, I am currently out of town and do not have drawing capabilities. As soon as I get back to my computer I will make a drawing for you. It really is quite simple though. Do you know what an optoisolator is? Do you have access to a store like Radio Shack? They sell a few different types of them. I don't know where you are located.

Take the voltage readings with a voltmeter. A scope is overkill but if you have that and no voltmeter then that will do.

Do you know who the manufacturer is?

I'll check back with you this evening. I'm in Ohio on the Eastern time zone.

BobK

[maxster03]

Hi Maxster03,

I have made an assumption that you are using a battery operated smoke alarm. We in the alarm profession call a 110vac or battery operated detector a smoke alarm. One that is made for alarm systems integration (wired in) is called a smoke detector.

Anyhow, I am currently out of town and do not have drawing capabilities. As soon as I get back to my computer I will make a drawing for you. It really is quite simple though. Do you know what an optoisolator is? Do you have access to a store like Radio Shack? They sell a few different types of them. I don't know where you are located.

Take the voltage readings with a voltmeter. A scope is overkill but if you have that and no voltmeter then that will do.

Do you know who the manufacturer is?

I'll check back with you this evening. I'm in Ohio on the Eastern time zone.

BobK

yeah i am using a Battery Operated Smoke Detector, Its a 9V Battery. Well i am Currently located in Bradford, England. but i think i can get a Opto isolator from here. Well the smoke detector is quite a cheap one, the company is Ei Electronics, basically i am doing a project on home alarm system in the university, well i have measured the voltages with both voltmeter and the scope, i have already mentioned the scope readings, it gives me the following readings with the digital voltmeter but they are changing all the time

red/black = 0.70V to 0.80V (not constant)
red/ white = 2.20V to 2.50V (not constant)

Well i have heard about the Opto isolator but i am familiar how it works and its functions.

Thank you so much for your help, i would be looking forward for the drawings

[BobK]

Hi Maxster03,

Sorry for the delay. My work schedule got changed around at the last minute Sunday afternoon. I have attached the file for your review. It should be self-explanatory.

HTH,

BobK

[maxster03]

Yeah tht was really help ful of you.

i just wanted to ask, can i use a bridge rectifier to convert a square wave signal into a DC signal, is it possible ??


Thank you for your help