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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Fire alarm in the fireplace. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Home, household, hobby When burning a fireplace or a sauna stove in a country house with wood raw materials, the combustion process must be controlled from time to time: throwing firewood, increasing traction, etc. The proposed electronic device can be replaced and reminded of this, signaling a decrease in the flame in the furnace (furnace ). I experimented a little and found that infrared alarms, it turns out, even react to a burning match with very little infrared (IR) radiation. But it was this knowledge that served as an impetus for the development of a combustion control device. With a bright flame at a distance of up to 1,5 m from the hearth, the signaling device is "silent". As soon as the fire in the stove or fireplace begins to die out, a signal sounds. But, for example, there is no reaction of the device to a flash using an IFC-120 flash lamp (and miniature flashes built into modern cameras). It is not difficult to assemble such a device even for a radio amateur without much experience and enjoy the work, well-deserved pride in creating a useful device with your own hands and gratitude from the household. The most expensive part of the device - an infrared detector (IR) - costs about 80 rubles. But it can also be used from an old remote control (RC) receiver installed on the TV. Color television receivers began to be equipped with such detectors back in the late 80s of the last century; a detector taken from there is also suitable (the remote control receiver board itself is not needed). Similar IR detectors are also installed in modern TV models - and they will fit for this design.
The supply voltage of the device is in the range of 5-7 V, it is related to the technical characteristics of the IR sensor. The supply voltage can be increased, for example, to 12 V, by adding a simple limiter-stabilizer to the circuit, consisting of a KS156A zener diode (or similar, for example, BZX55C) and a 0,82-1 kOhm limiting resistor connected in series with it. The anode of the zener diode is connected to a common wire, and the junction point of the zener diode (cathode) and the resistor is connected to terminal 2 of the IF1 sensor. In this case, the supply voltage is applied to the limiting resistor. The current consumption of the device does not exceed 25 mA, 20 mA, from which the sound capsule "takes". Principle of operation Oxide capacitor C1 smoothes power supply noise. The normal state of a sensitive IR detector is a small high output level (pin 3 of IF1). If there is an IR signal in the "responsibility" zone of the detector, there are negative pulses at the output 3 of the detector. Polar capacitor C2 serves to reduce the influence of random and extraneous interference. It is especially necessary when there is radio equipment with remote controls in the same room (as a rule, they use the IR spectrum to transmit a signal over a distance, for example, an alarm device is installed in the living room and controls the operation of the fireplace). If the device is used in a bath (and where such interference is unlikely), it is advisable to exclude C2 from the circuit. Negative pulses of small amplitude are insufficient to control an audible (and even light) signaling device or relay. Therefore, passing the peak detector on the elements R1, VD1, they enter the gate of the field-effect transistor VT1, which acts as a current amplifier. The transistor controls a sound capsule with a built-in audio frequency generator (AF) - HA1. At the end of the fireplace insert, the signaling device can be turned off by the switch SВ1. The device does not need adjustment. The oxide capacitor C3 in this circuit is an element that provides a delay in turning off the sound. This is necessary so that the signaling device does not react to the flickering of the flame or a short-term decrease in combustion. So it was possible to ensure that the "alarm" will sound only when the flame is actually extinguished. The larger the capacitance of the capacitor C3, the greater the inertia of turning on the alarm can be achieved. Within very small limits, the sensitivity of the device can be adjusted by changing the resistance of the constant resistor R1. About details The PRM6936 IR detector can be replaced with a TSO1736CB1 or equivalent. The conclusions are considered in order, turning the detector with the convex side towards you. For the TSOP1736CB1 device, 1 and 2 leads are located side by side, then after 2 mm from the second, the third one goes. Polarity reversal of the detector is not allowed. Oxide capacitors - type K50-29 or similar. The BST70 field effect transistor can be replaced with a BS170 or similar. Both resistors are of the MF-25 type. Diode VD1 can be replaced with KD522, D220, KD503 with any letter index or foreign analogue 1N4148. Sound capsule HA1 with a built-in AF generator for any voltage of 3 - 6 V, for example, TR-1203Y. The capsule must be included in the polarity indicated on the diagram. Instead of it or in parallel with it, you can even turn on a low-current electromagnetic relay with a supply voltage of 5 V, for example TRU-5VDC-SB-SL. Such a solution may be useful in the future (see text below). There are so few elements in the circuit that I did not develop a printed circuit board, I used a standard perforated "blank" with metallized holes for the leads, and I made interconnections using MGTF-0,6 wire. The photo shows a ready-made signaling device in the case (on the right - a signaling capsule HA1).
Features and perspective of application The device responds well to an open flame; at a distance of up to 0,5 m, the signaling device works even on a lit match. From this we can draw a simple conclusion that on the basis of the proposed device it is possible to manufacture a fire alarm. The principle of operation is the same - from an open flame, and during the day the efficiency of the signaling device is the same as at night: after all, the device does not react to light, not to heat, not to the flicker of flames, but to the infrared component in the spectrum of fire, and it from time to time day does not depend Such a signaling device may become especially necessary outdoors, in open spaces, in forests, in villages, on the street. In these places, a conventional fire detector that reacts to smoke is practically useless. In cases where it is required to control a powerful load (with a current of up to 6 A in a 220 V network), the load should be connected through a relay. For example, a submersible water pump. The device can also be useful for controlling the operation of any remote control ("catches" both direct and reflected from the walls of the room infrared beam "invisible" to a person); for troubleshooting and monitoring the operation of computer peripherals and cell phones with an infrared port; for "monitoring" of the premises, storage, in which alarm means invisible to a person can be installed, triggered by crossing the infrared beam (as in films about agent 007) and in many other cases. The device is easy to assemble. Author: A.Kashkarov
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