TGS2600 gas sensor module problems - Page 1
Forum section: electronics / projects

author: Silenus
author_rank: Contributor
timestamp: September 19, 2014, 10:26:10 am
content: So I went and bought myself aTGS2600gas sensor from amazon, the sensor is housed in a module done by Sainsmart, similar tothis. From the TGS2600 documentation, the sensor detects a gas and changes its resistance which can be read using an external resistor as a voltage divider. Sainsmart are pretty terrible at documentation, so I haven't been able to find an exact schematic of their module circuit, but by inspection I have a fairly good idea what it is.From what I can see on the board, there are 4 pins, GND, VCC, A0 and DO. There is a variable resistor (P 103 302B on the blue housing), an LM393 dual opamp, a few resistors, a cap and an LED.When I hook up the sensor to 5V Vcc, I see around 4.4V on the D0 pin and a few hundred mV on A0. No matter what I spike the sensor with, these values wont change. I have even put it directly next to a test tube of 98% ethanol. Since this is a module designed for this sensor, wouldn't something as simple as getting it to register any change at all be simple?I am unsure whether the sensor is broken (although it measures ~83 ohm across the electrode as per the TGS2600 datasheet) or whether the module board is broken. Anyone have any advice as to what could be the problem?

author: SeanB
author_rank: Super Contributor
timestamp: September 19, 2014, 03:47:15 pm
content: Try loading the pins with a resistor, and see if things change. Likely the heater is not energised, so the sensor is sitting idle. Photo of the board will help.

author: Silenus
author_rank: Contributor
timestamp: September 20, 2014, 01:43:05 am
content: Quote from: SeanB on September 19, 2014, 03:47:15 pmOne thing I noticed that was different to other sensors similar to it is that the sensor doesn't get hot when its powered on. I will check what the voltage across the heating element is when its powered. Curious, what does loading the pins with resistors do?If you want a picture, it is exactly the same module as the above hyperlink <this> except the TGS2600 in place (which is mostly the same).

author: SeanB
author_rank: Super Contributor
timestamp: September 20, 2014, 04:41:17 am
content: Likely the one pin is to enable the heater, so it needs to be either pulled to Vcc or ground via a resistor to power the heater pellet. Done so that the control unit can do power management and turn off the heater when needed. Likely it will need a resistor in the range of 10R to 100R to get it to work. Check where pins 1 and 4 of the sensor connect to, one will be Vcc or gnd and the other will go to one of the pins. Then connect it to the other supply to turn on the heater, probably via a 10R resistor and supply it with 5V. Load resistor is likely on the board already.

author: Silenus
author_rank: Contributor
timestamp: September 20, 2014, 07:36:12 am
content: I found a schematic (finally) of the module board they are usinghere. Still not sure why they have 4 pins at the bottom of the board, yet in their description they say the board only has 3 outputs: Vcc, GND, Output. Any idea what these 4 pins mean?