Gas analyzer circuit


Posted on Jul 13, 2012

The circuit shows a simple yes/no gas detector. Three 1.5-V D cells are used as a power supply, with SI acting as an on/off switch. The heater is energized directly from the battery, while the electrodes are in series with a 10 k resistor. The voltage across this resistor is monitored by a pnp transistor. When the sensor is in clean air, the resistance between the electrodes is about 40 k, so that only about 0.9 V is dropped across the 10 k resistor. This is insufficient to turn on the transistor, because of the extra 1.6 V required to forward bias the light emitting diode (LED) in series with the emitter.


Gas analyzer circuit
Click here to download the full size of the above Circuit.

When the sensor comes in contact with contaminated air, the resistance starts to fall, increasing the voltage dropped across the 10 k resistor. When the sensor resistance falls to about 10 k or less, the transistor starts to turn on, current passes through the LED, causing it to emit. The 180 ohm resistor limits the current through the LED to a safe value.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Cash Register circuit
EEPROM DAC with DS interface
Morse Keyer circuit
Hall-Sensor Current Monitor
40M Cw Transmitter Circuit
New latest Simple SWR Meter 2.4 GHz 20 dB Directional Coupler
1.5W Audio Amplifier with IC SSM2211
stk415 090e 2x50 watt stereo
Digital to analog converter using R 2R ladder network and 741 op amp with simulated output waveform
Ensemble RXTX Builders 1
An adjustable bounce lighting circuit



Top