Device, scheme of which is given below, is used to gas leak detection.

The sensor detects methane, ethanol, hydrogen, isobutane. You can change this list by simply applying another sensor in scheme. Comrades from the office Figaro produce a bunch of different of sensors for detecting various gases.

Diagram of the device such (to get the bigger scheme, it is necessary to press on a little):

A power source for LDS

(click to enlarge)

Will go quickly in terms of functional groups scheme.

Thus, the sensor SE1 is a plate with some oxide, which is heated by an embedded heater.

In pure the air sensor resistance is approximately 10 ohms. When the appearance in the air of particles in the gas, the resistance of the sensor begins to fall - the stronger, the greater the gas concentration. When a certain threshold comparator on the chip DA2 changes its state, and starts working generator DD1.1. In this connection, blinking led HL2 and terrible beeping beeping buzzer SP.

Node DD1.3 provides a delay time of approximately 2 minutes. This is due to the fact that the sensor heater needs time for it to warm up and recover. Indicator HL3 just lights up after 2 minutes, and signaling of the sensor to work.

Eats the whole thing from a regulated source voltage 5 volts on the chip DA1.

Details

The symbol on the schematic

The value

Note

R1

1K

AC, multiturn

R2

220

R3, R13, R14

470

R4, R9, R11, R12

10K

R5, R7

3.3 kOhm

R8, R15

Am

R10

1m

R6

10K

AC, multiturn

C1

Thu

C2, C7

0.1 μf

C3, C6

Thu

C5

Mcfjw

VD1

KTS405

VD2

CD

Bourgeois analogue 1N4148

HL1

Green led

HL2

Red led

HL3

Yellow led

VT1

CTB

DA1

CREA

Bourgeois analogue LM317

DA2

CRUD

Bourgeois analogue LM358

DD1

CTL

Bourgeois analogue HCF4093

SE1

TGS2611

Depends on the type of gas.

T1

Any voltage on the secondary winding 7-9 volts and a current of 300-400mA

SP

Any with built-in generator

About configuring

First of all, break the positive power supply pin diagram (somewhere in the region of the first led) and a configurable voltage regulator resistor R1. Set of 5 volts as accurately as possible. Then restore the schema and connected to the network. After about 2 minutes should light up led HL3. Again measure the voltage at the output stabilizer, and if necessary, adjust it. Measure the voltage at pin 2 of the chip of DA2 and the resistor R6 installed on a couple of tens of millivolts less measured at the output 3 of the same chip. Next, take the lighter (gas of course) and begin to put gas in the face of the sensor. Must light up the led HL2 and squeaked buzzer. The sensitivity is adjustable by the resistor R6.

This can be considered finished setting.

In conclusion I would like to note that to install the sensor in wet areas is not recommended because of its resistance depends on humidity. Therefore, do not install it directly over or near home a gas stove.

Publication: www.radiokot.ru, www.cxem.net

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