CIRCUIT IDEAS 94 APRIL 2013 | ELECTRONICS FOR YOU WWW.EFYMAG.COM D. MOHAN KUMAR Sensitive LPG Leakage Alarm a few discrete components. GS1 is a six-pin gas sensor that can detect very small traces of LPG in the air and has a swift response time. However, it has very less sensitivity to alcohol and smoke. The sensor’s out- put is in the form of resistance. As indicated in Fig. 1, the pins of GSI are H, A and B, two each on either side. H pins are for the heater with no H ere is an ultra-sensitive LPG sensor that generates loud beeps when it senses any gas leakage. It detects vapours of lique- fied petroleum gas anywhere between 200 and 10,000 ppm and drives a pi- ezobuzzer to catch attention for imme- diate action. The buzzer beeps until the concentration of gas in the air decreases to a safe level. The circuit uses an MQ6 gas sensor, which is designed to sense LPG, propane and isobutane gases. Circuit and working Fig. 1 shows the circuit of the LPG sensor. The circuit is built around 5V voltage regulator 7805 (IC1), gas sensor MQ6 (GS1), counter IC 4060 (IC2) and polarity. Input pins A or B and output pins A or B can be connected either way round. The coil heater inside the sensor can be easily heated with 5V DC. If pin A is connected to 5V DC through variable resistor VR1, use pin B as the output or vice versa. Both A and B pins can be shorted. In short, H pins are connected to positive and negative rails, A or B pin to 5V DC, and B or A for output. The resistance value of GSI is dif- ferent for various kinds and concen- tration of gases. So when using this sensor, sensitivity arrangement is very important. For accurate detection, it is necessary to calibrate the sensor for 1000 ppm of LPG concentration in the air with load resistance of about 20 kilo-ohms. (In the datasheet, the load resistance range of MQ6 is mentioned as 10 kilo-ohms to 47 kilo-ohms.) Preset VR1 is used to adjust the sensitivity of the sensor to a par- ticular gas concentration. Output from the sensor is connected to the base of transistor T1, which acts as a switch to trigger the alarm gen- erator built around IC2. IC2 is a binary counter IC that oscillates using capacitor C2 and resistor R5. Transistor T1 controls the reset pin (pin 12) of IC2. When SANI THEO Test Points Test point Details TP0 0V, GND TP1 12V TP2 5V TP3 0V when sensor is exposed to LPG and LED1 blinks TP4 5V square pulse LED1 BATT.1 12V C2 0.22u R5 100K R4 1K R7 1K R1 100E R2 1K R6 1M R3 10K GND TP1 TP3 TP0 T1 BC547 T2 BC547 PZ1 PIEZO 16 VDD 12 MR 11 RS 9 CEXT 10 REXT 8 GND 6 Q6 14 Q7 13 Q8 15 Q9 1 Q11 2 Q12 4 Q5 5 Q4 7 Q3 3 Q13 IC2 4060 BUZZER GS1 MQ6 SENSOR VR1 4.7K 1 2 3 IC1 7805 C1 100u,25V A A H BHB TP2 TP4 R8 20K Fig. 1: Circuit of the sensitive LPG sensor Log on to www.electronicsb2b.com and be in touch with the Electronics B2B Fraternity 24x7 ELECTRONICS INDUSTRY IS AT A www.electronicsb2b.com Read more stories on LED at www.electronicsb2b.com • LED commercial lighting: Look for new technology and innovative products • Prices of LED lights to fall by 10-12% • Industrial LED lights: Let your choice be based on technology, rather than price • Mirc Electronics ventures into LED lighting with Onida and Igo • How LED players can participate in govt projects • LEDMA to develop LED standards soon • Unhealthy practices galore in Indian LED market • Immense business potential brewing in Indian LED lighting market TOP LED STORIES