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Power failure alarm

EdgarAndre

May 14, 2024
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Hi, I am in search for help as i am a beginner in electronics. The circuit i want to build is an alarm for power failure with a two hour timer. . The diagram i include was generated by Chat GPT but it is not clear enough for me to place the components on a circuit board. That circuit is powered by a 9 volt wall plug power supply. A 9 volt battery is included to power the alarm. The timer alarm could also be adjustable. If you know of any kit available or references it would be appreciated.
 

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Delta Prime

Jul 29, 2020
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AnalogKid

Jun 10, 2015
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Your question is missing a *lot* of detail. What is the relationship between the timer and the alarm? Do you expect the battery to power the alarm for 2 hours? 2 hours is a loooong time for a 555 timer circuit; even the CMOS version would be iffy..

Rather than have us waste time trying to guess what a chat circuit might be trying to do, please describe what it is you are trying to achieve.

ak
 

AnalogKid

Jun 10, 2015
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That circuit has several problems. Why is there a 10 K resistor in series with the beeper. That will make for a very quiet "alarm", if the beeper sounds at all.

Without connections dots, it is impossible to say if the circuit will even work.

It shows the 555 powered by only the battery. The bipolar 555 as indicated can draw up to 15 mA with the output in the low state. This is an unnecessary drain on the battery.

Why is the 555 configured as an oscillator?

Assuming certain pins are in fact connected, D3 will prevent the oscillator from running when AC power is available. But that is not what is required.

ak
 
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AnalogKid

Jun 10, 2015
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High impedance input it beeps at 85 decibels after you hear it be you won't hear anything at all.,. If you're up close

Nope.

With the components shown, the 555 is pulsing power to a self-contained piezo beeper, the kind with a 1-transistor oscillator built-in. In very round numbers, the 555 oscillator is driving it at 1 second on and 1 second off, not at the 2 kHz to 4 kHz needed for direct drive to a bare piezo element.

ak
 

EdgarAndre

May 14, 2024
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Your question is missing a *lot* of detail. What is the relationship between the timer and the alarm? Do you expect the battery to power the alarm for 2 hours? 2 hours is a loooong time for a 555 timer circuit; even the CMOS version would be iffy..

Rather than have us waste time trying to guess what a chat circuit might be trying to do, please describe what it is you are trying to achieve.

ak
Sorry if I wasn't specific enough in my description. I want an alarm for electrical failures. It would be powered by a 9 volt DC 500mA wall transformer and a 9 volt battery would be used to operate the buzzer after the loss of the main power supply. I would like the alarm to sound ( 1 minute would be enough) after the power has been out for two hours. Another option would be that the duration of the timer could also be adjustable from two to four hours. A switch would turn off the alarm.
 

AnalogKid

Jun 10, 2015
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That is a significant change from

an alarm for power failure with a two hour timer.

So now the beeper beeps for only one minute, but after a 2 hour delay? That would be a 2 x 555 circuit, one for the 2-hour delay and one for the 1-minute beeper time. But there is another approach.

2 hours is a loooooong time for a simple R-C timer circuit, even one with a CMOS 555. An alternative is a CD4060, which is an oscillator plus a 14-stage binary divider. This effectively reduces the size of the timing capacitor by a factor of over 8000, so you can use a much more stable cap.

What is your skill set for wiring up a small circuit?

ak
 

AnalogKid

Jun 10, 2015
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Here is a first pass at a dual-555 solution. Of note is the very large timing capacitor for the 2-hour delay. Cleaned-up version to come.

ak
!!Power-Fail-Alarm-1-c.gif
 

Bluejets

Oct 5, 2014
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It is quite feasible to do with a contact free arrangement so therefore no mains intrusion, and an Arduino.
Advantage of the Arduino is it can be put to sleep and draw very little current until it is woken up, obviously by a change of state of the detector.
The detector will naturally draw some small amount of current also but would be minimal in the off state one would imagine.

Ralph Bacon video here which would need possibly some modification to the code to have the Arduino do what you want but it's pretty much all there.
.............and safe given the non-contact sense.

 
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