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Freestanding Smoke Detector MCU
  • Written by manager
  • Written date 2022-10-05 00:00:00
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Freestanding Smoke Detector MCU


There are various types of Fire alarm systems. Among them, a smoke detector is a device that typically detects smoke as an indicator of fire and informs the outbreak of a fire in the form of sound or light.


In large commercial and industrial buildings, a network-type connecting to the central fire alarm system is mainly used, and a single-type is mainly used in general houses.


The single-type smoke detector uses batteries as a power source, and the amount of current consumed by the MCU is critical for its operation. In such systems, the batteries are aimed at being used for 10 years once installed.


ABOV’s A96L416 MCU features a 2ch Op-amp, a 10bit ADC, and a constant current source for the application of a single-type smoke detector. Most important thing is that A96L416 is designed to consume up to 4uA of current when entering Stop mode with a built-in 32kHz IRC on.


A96L416 is suitable for low power products, with a wake-up time less than 16uS in Stop mode.

The figure below shows an evaluation board block diagram of a single-type smoke detector.


               [Figure 1] Freestanding Smoke Detector Evaluation B/D


As shown in the block diagram, users can check the amount of smoke in the air, using the MCU and smoke detector circuits on the evaluation board. The amount of smoke in the air is digitized by the ADC built in the A96L416 MCU, and when the digitized ADC value exceeds the threshold, a fire alarm is generated. In the development environment, fire alarms are not generated by sound but are displayed by LED indicators.


Developers can use external components to communicate with your PC via OCD or USART to debug and store the raw data values.





 

[Figure 2] Digitizing the amount of smoke using ADC


The example code provided by the evaluation board uses the ADC to digitize the amount of smoke, following the sequence shown in the figure above:

1.      Op-amp is enabled, and has at least 300uS of stabilization time.

2.      ADC module is enabled.

3.      IR LED is turned on.

When the IR LED is turned on, light is reflected by smoke in the air (dust particles), sent to the photo diode, amplified by the Op-amp, and transmitted to the input of the ADC. The ADC starts at approximately 8uS before the peak point, to detect the moment when the signal is peak.

As shown in the figure above, assuming that the peak point of the ADC’s input signal is at 93uS after the IR LED is turned on, the ADC starts at 8uS before the peak point, which means the ADC starts after a delay of 85uS.

You can determine if a fire has occurred by reading the ADC data after the ADC conversion is completed.

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