How to Correctly Design a DIY Smoke Sensor System

By Kaushik Hazarika. He is an embedded project consultant and inventor of a low-cost LED inverter.

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The ATtiny can reach about 1uA in low-power sleep. Because we only need to periodically check for smoke a rate of pulse can be selected every4seconds after that put the ATtiny into sleep and wake it up every once and awhile.

For this watchdog timer is good, usage as follows:

A watchdog can reset the processor when it gets locked into an endless loop – also known as going off into the weeds. This is a good way to protect a project needs to run all the time without user intervention.

A watchdog can wake the processor from deep sleep. When we put a microcontroller into deep sleep, we can use the watchdog timer as an interrupt, causing the processor to return to normal 8MHz (without a full reset).

The watchdog is just a counter. When that counter gets to the size the user specifies, the processor will either reset or an interrupt will be triggered. Reset can be useful (as explained above), but an interrupt is what we need.

Sample code is very easy to understand.

setup_watchdog(6); //Setup watchdog to go off after 1sec
sleep_mode(); //Go to sleep! Wake up 1sec later and check smoke

A detailed code can be found in sparkfun site URL

The sensing accuracy can be test verified, a distance of 2 meters is a good reference to test.

The alarm should be loud enough to hear must reach 3 rooms so that the protected people can escape on time. Also, to accommodate this loud beeping device piezo buzzers are best choice.

The cases to be used are recommended fire-retardant cases.

Place the smoke sensors in a metal shell separated by air, very simple, kept on tape the circuit and battery. Use a dry 9v to be safe any lithium will explode in case of fire.

CO2 Detection

The method employed by CO2 resonance type fire detectors, because it detects the resonant radiation of the carbon dioxide gas generated in a flame, has a high level of detection accuracy. The spectrum of resonant radiation of the carbon dioxide gas generated when materials burn extends across the range from infrared to ultraviolet, but it is characterized by having a large peak at a wavelength of 4.4µm in the mid infrared range. The spectrum of a typical flame is shown [with other spectra] in Figure 1. Infrared rays are generated by low-temperature bodies, such as human, and by high-temperature bodies, but since they do not have the sharp peak of carbon dioxide gas resonance, the distinction of that peak can be used to detect that the radiation source is a flame.

Configuration of a fire detector is shown in Figure 2. For the infrared light sensor, a pyroelectric type sensor, a thermopile, or other sensor is used. A pyro-electric type sensor utilizes the phenomenon that an electric charge is generated on the surface of a dielectric crystal when heat is applied to it. A thermopile is a row of thermocouples—specifically, a number of thermocouples are connected in a straight row in order to increase the sensitivity and has essentially flat wavelength characteristics. A first band-pass filter for [the wavelengths of] carbon dioxide gas resonance is placed in front of one sensor and a second different band-pass filter is placed in front of another sensor, and the strength of the infrared light reaching each sensor is detected. In the processing circuit, the ratio of the two strengths is measured and by the fluctuation it is determined whether the flame is being disturbed.

In addition, optimizing these parameters according to the use conditions, very precise fire detection can be done. Figure 3 shows an external view of the evaluation device. In both the left and right light receiving portholes, several sensors are mounted, and the device is configured so that the outputs and internal processing status can be monitored.

Combination to Networks

When a fire occurs inside a home, the important factors that help to minimize damages are: quick detection and notification. So essentially well-connected sensors will be a better design.

The sensors can be RF based or Wi-Fi network enabled. Provided Wi-Fi hot-spot must be on ground where fire can’t reach.

This kind of combination sensor, in addition to a fire detection function based on conventional infrared detection, has a relatively high degree of usefulness. Making a suitable DIY design can lead to a line of economical products and safety for all people. Hope this paper caters to designers who need system planning and make DIY deployable sensors.


 

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