27904 Parallax Inc, 27904 Datasheet - Page 2

• Manufacturer Part Number: 27904
• Description: ALCOHOL BENZINE GAS SENSOR
• Manufacturer: Parallax Inc

Specifications of 27904

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Precautions
Be aware that the gasses detected by these gas sensors can be deadly in high
concentrations.
monoxide (CO). Propane Gas (LPG) can leak from propane grills and furnaces and Methane
(CH4) can be found in animal farming areas. Always be careful to perform gas tests in well-
ventilated areas.
THESE GAS SENSOR MODULES ARE NOT DESIGNED FOR OR APPROVED FOR ANY
APPLICATION INVOLVING HEALTH OR HUMAN SAFETY. THESE GAS SENSOR MODULES ARE
FOR EXPERIMENTAL PURPOSES ONLY. PARALLAX, INC. ABSOLVES ITSELF OF ALL LIABILITY
AND RESPONSIBILITY ASSOCIATED WITH THE CUSTOMER'S USE OF THESE GAS SENSOR
MODULES AND IS NOT RESPONSIBLE FOR ANY BODILY INJURY, DEATH OR PROPERTY
DAMAGE AS A RESULT OF USING THESE GAS SENSOR MODULES.
Connecting and Testing
The gas sensor canister plugs into the socket on the front of the module. The gas sensors are essentially
resistive devices and are not polarized, so there is no need to be concerned about plugging it in
“backwards.” It will work in either orientation.
The 4-pin SIP header on the Gas Sensor Module makes it easy to connect to a breadboard or SIP socket.
The four connections are defined in the table below. Connection to a 5V microcontroller, such as the
BASIC Stamp
the alarm signal and the other an output for controlling the internal heater.
For a 3.3V microcontroller such as the Propeller
required from the ALR output to the Propeller chip input pin. For the Propeller to control the heater
switch input (HSW) you would need an NPN switching transistor, such as a 2N3904 and a 1 kΩ resistor.
The schematic for this connection is shown below.
Copyright © Parallax Inc.
®
Switching circuit for the Propeller
chip. Note: HIGH signal is
required to turn on heater due to
inversion of signal by the
transistor.
module, would be pretty straight forward and require two I/O pins; one input for detecting
Automotive exhaust and charcoal cooking grill exhausts emit carbon
Gas Sensor Modules (#27930, #27931, #27932, #27904) v2.2 8/2/2010 Page 2 of 6
TM
chip, a 3.9 kΩ (10 kΩ could be used) resistor would be