HI

With my lack of electronics knowledge I m trying to build a battery powered CO monitor using a TGS2442 CO sensor and PICAXE-08M2+ chip. Could some1 plse help me with interfacing the sensor to the microporocessor with circuit diagrams and coding. The monitor is meant for domestic use.

plse help ne1

 

There's a sample app in this Figaro TGS2442 app note. I don't like several things about it as it doesn't seem to be practable, but as I don't use a PICAXE it may be compatible.

First off, it asks for two open drain outputs. These can be simulated on most micros by driving an output to zero, then changing it to an input. However, that only works for digital signals. These are analog points and you shouldn't drive a digital input with an arbitrary analog signal. You could add FETs or transistors to get a true open drain output there.

Next is the values of Ra (I don't know it) and Rb which they recommend 300K. That would give too high an input resistance to most A2D converters, so you would need an op amp buffer before S-In.

Anyway, all that takes 5 of the 6 I/O pins of your chip, so is a single bit output acceptable for your uses?

 

hi thanks for the reply....1st of ol...i was wandering wat r the purpose of Ra and Rb and do i really need them coz i believe i wud only need S-in to trigger the alarm as da chip will be monitoring it constantly and react to a set trip and 2ndly cud u simply wat u meant by da open gate drain paragraph.....coz my understanding is dat nly need to turn on da heater 4 14ms per evry 1s cycle nd i cud use PWM for dat.

 

hi thanks for the reply....1st of ol...i was wandering wat r the purpose of Ra and Rb and do i really need them coz i believe i wud only need S-in to trigger the alarm as da chip will be monitoring it constantly and react to a set trip and 2ndly cud u simply wat u meant by da open gate drain paragraph.....coz my understanding is dat nly need to turn on da heater 4 14ms per evry 1s cycle nd i cud use PWM for dat.

Sorry, you lost me after you started to wander off.

 

sory abt dat....wat i wud like to knw is wat is the purpose of the two open drain outputs RL1 and RL2 and do i really need them....i have a presentation due in 4wks nd wud like 2 complete building a CO(detector/monitor/sensor) and go abt doing it the easiest way.can u help me plse???

 

That's all covered in the app note I linked for you. You need to understand the device cold to make that determination. It looks to me like RL2 is only used in failure detection, but if that is truly correct and is not necessary in your design are questions you should be asking yourself.

And don't forget Google is your friend. There isn't much prior art out there on this particular device, but there is some for similar devices.

 

i banged my head on those app notes but they just fly over my head therfore i was thinking of using da MQ-7 CO sensor instead...it may require lots of power hence i will use an adaptor but do u reckon the interfacin/connection to da microchip will be simpler than the TGS2442 and it will only require me to read 1single analog input.