Resettbale alarm

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kwame

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Hi ia m from africa. I want to install an alarm for my thermostat when the temperature goes too high and siren sounds,i want to use a resettable button to silence the alarm. when the the alar, is in this mode,i want the siren to be still able to sound,when temperature goes beyond minimum/maximum limit or when there is power outgage.
In otherwords,when the siren sounds and it is resett, i do not want the alarm to go off and continue to work.How do i go about this?

kwame
 
Is this right:

1. The temperature monitor circuit that provides an output if minimum or maximum limits are exceeded?
2. The alarm circuit that when silenced, will automatically be ready to alarm "after" the temp returns to the normal range?
3. The alarm circuit that when silenced or not, will automatically be ready to alarm after a power outage, when power is restored?
4. No alarm during a power outage?

Ken
 
The African guy wants to turn off the warning siren which is deadly. Here in civilization we use smoke detectors that alarm when a fire is starting. We investigate if there is a fire or not then we push the "silence" button when the fire is not burning anymore.

Behind my home is a rented house. The idiot woman there poured gasoline in a garbage can inside the garage then lighted it on fire to kill maggots inside the garbage can. I saw the black smoke and ran around the block to watch her garage and house on fire, the car in the driveway on fire then the house next door catch on fire. The fire trucks could not drive up the street because too many cars were parked on the street.
 
Has the stupid women ever heard or insect killer spray?

Here in the UK, the bins are made of plastic and people have set fire to other people's bins in order to bun their house down.
 
wants to turn off the warning siren which is deadly
Click to expand...
I agree that generally this is not a good idea. But we don't have enough detail to know if this is in a life safety situation...or just a personal convenience thing. I modified the blood bank refrigerator alarms in our hematology labs to make them automatically re-alarm after 5 minutes. This, because someone silenced a high temp alarm, got distracted, and we lost a whole cabinet of autologous blood donations.

Ken
 
I think the stupid people should be eliminated when they are born.
They didn't notice me and I am still around. (smiley)
 
Ressetable alarm

Hi ken
1.i have installed a thermostat to help regulate temperature .
2.I want to install a siren so the When temperature goes too high to 39 degree celsius,it will sound to draw my attention.
3.Similarly ,when temperature falls to 36 degree the siren should sound to draw my attention.
4.When there is power cut (which is frequent here)it want the siren to sound so that i can start the generator.
5.When siren sounds due to any of the above reasons, i want it to be silent when i move the toggle switch up/down.
6.When i silence the siren with the toggle switch, i want the siren to be able to sound anytime the above conditions(2,3,4) occurs.In otherwords, i do not want the alarm to go off.


 

2, 3 & 4 can be done using comparators.

Voltage can be measured using a zener reference and a potential divider.

Temperature can be measured using a thermistor.

5 & 6 can be done with a bistable multivibrator or an SCR.

What size is the battery?

How long does it need to be on standby for?

How much current does the siren need?
 
siren

Hi hero controlling the temperature is not a problem.I have a relay and miniature relays ready to install the thermostat.The thermostat already has a thermistor inside.
Main bother is how to make alarm resettable.
 
siren

Hi hero controlling the temperature is not a problem.I have a relay board and miniature relays ready to install the thermostat.The thermostat already has a thermistor inside.
Main bother is how to make alarm resettable.
 
correction

1.i have installed a thermostat to help regulate temperature .
2.I want to install a siren so the When temperature goes too high to 39 degree celsius,it will sound to draw my attention.
3.Similarly ,when temperature falls to 36 degree the siren should sound to draw my attention.
4.When there is power cut (which is frequent here)i want the siren to sound so that i can start the generator.
5.When siren sounds due to any of the above reasons, i want it to be silent when i move the toggle switch up/down.
6.When i silence the siren with the toggle switch, i want the siren to be able to sound anytime the above conditions(2,3,4) occurs.In otherwords, i do not want the alarm to go off.










 
I've told you before, you need another temperature sensor to monitor the temperature.

Why do you keep repeating yourself? We understood what you wanted to do the the first time, giving more information such as a schematic or telling us what temperature the thermostat is operated at, would be better.
 
OK, I'm going to give this a shot. Probably should have just done a block diagram...but go ahead and tear it apart.

I couldn't find a circuit for a window comparator with hysteresis on both levels. No Values on most things because I don't know.

U1 sets an offset and gain to get a good output from the thermistor half bridge. U2 forms a comparator with hysteresis, so Q1 is turned on and holds the relay on as long temp is within range. The alarm/silence circuit (thanks mvs sarma), is switched by the relay and powered by a Ni-cad battery that is charged by the constant current LM317. SW1 silences the alarm, but the LED D1 stays on to indicate that the system is still in alarm. Everything is powered by a wall wart. If power is lost the relay drops out and triggers the alarm.

Ken
 

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Just a few comments:

I'd probably go with a voltage comparator instead of a relay.

There shouldn't be any need for hysteresis, if it triggers an SCR or a flip-flop.

I'd probably include a bypass resistor across the buzzer in case the current through it drops below the SCR's holding current as it oscillates.

We haven't been given enough information anyway, like at what voltage should the alarm sound at?

Is it operating off the mains or a battery?

I'll have a go anyway, just because I've never done this before.
 
The battery is goinng to be powered from the 12v battery.What do you mean by "what voltage should the alarm sound at?''

 
When the battery voltage drops below a certain voltage, you want the alarm to sound?

At what voltage do you want the alarm to sound at?
 
When the temperature drops below a certain threshold, i want the alarm to sound.I am not referring to voltage.Thanks.
Hero999 said:
When the battery voltage drops below a certain voltage, you want the alarm to sound?

At what voltage do you want the alarm to sound at?
Click to expand...
 
Hero,

I think kwame wants the alarm to sound when he looses "mains" power, not battery power....or when the temperature exceeds the high and low limits of 36C or 39C. My guess is that the loss of mains power is all or nothing.

Ken
 
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