Output of the FMA Thermopile Sensor?

[jahibo]

Hi
I've been searching the internet looking for some information about this sensor but didn't find anything...

For my UAV-project I'm using a 2-axes-thermopile sensor-board from scalerobotics.com. Now I saw that the sensor contributed by FMA as a replacement module for their Co-pilot is so much cheaper - but don't now what kind of output I'd get...
Might be a Voltage varying between ~ 1 and ~4V similar to the board used by the guys from the paparazzi-project.

Would be very cool to get some information or maybe measurements.

thanks

so long Jan

[Tom Harper]

Jan,

The sensor has four wires - +V, 0V, X, Y. Inside the box there are four thermopiles, some feedback resistors and a dual op amp that has a rail to rail output swing.

I haven't looked at the signals yet but I assume they swing from +2.5V +- 2.5V. Since the rail to rail op amp costs extra money they must use the feature.

Tom

[jahibo]

Hi,
thanks, didn't expect getting an answer within a so little span of time...

At the moment I've to do some preparations for my exams but maybe during the late of summer my UAV will get into air - my actual setup consists of a IR-Sensor combined with a digital gyrometer in order to avoid pitch oscillations because of the IR-Sensor's mearurement error.

greets Jan

[Unterhausen]

http://www.recherche.enac.fr/paparazzi/wiki/index.php/Sensors
the papparazi project is pretty interesting, might want to look at all the pages

[Zbig]

FMA sensors are powered by 3,3V. With balance state there is 1,65V on outputs. Depending od wheather conditions (and tilt of course), output voltage changes by hundreds of miliwolts.

[Tom Harper]

Zbig,

Thanks, I was wondering how much signal they get out of the module.

Is the Papparazi schematic correct? A quick visual looks like:

1) IR output with LP filter cap to ground
2) IR output with LP filter cap to ground
3) Power supply with filter cap
4) Power supply with filter cap

Do you have a schematic?

Tom

[Zbig]

In sunny day it is something like +/- 0,9V when one sensor is pointing ground and opposite i pointing sky, but do not lay on it and calibrate sensivity in different weather conditions and surfaces (grass, asphalt, water) - it changes significantly.

In my application there are caps on +Vcc (47uF and 100nF), but output is connected directly to the ADC input of Atmega32 (without cap)

[AntonK]

The gain/output per degree temperature difference depends on the input voltage. The typical FMA sensor is set to use a 5V input, with 0-5V output. Of course its very difficult to get to the extremes. You can use these in an autopilot on 3.3V as we do in paparazzi with no problems. Some have made a resistor change to change the output gain of the sensors due to some saturation at high temperature differences. As for the schematics on the paparazzi CVS yes I believe they are correct, at one time a resistor value was wrong, but its been corrected.

Anton

[Zbig]

The typical FMA sensor is set to use a 5V input
In my FMA Copilot it is powered by 3V. It's good to know that it works well with 5V power.

[AntonK]

I dont understand why the FMA sensor would use 3Vs. Standard RC equipment is 5V, where do you get 3volts from? you have a seperate regulator?

AntonK

[Zbig]

I dont understand why the FMA sensor would use 3Vs. Standard RC equipment is 5V, where do you get 3volts from? you have a seperate regulator?
AntonK

Probably FMA Copilot has got internal 3V stabiliser, and uses internally 3V. A lot of receivers use internal stabiliser to avoid interferences and to separate from wide range of power voltage from battery (typically 4,4...7V when used without BEC).
I've just measure this voltage directly on sensor's connector in my working FMA Copilot.

[AntonK]

can you describe what you mean by on the sensor connect? are you talkiung the output of the sensor? Ive seen the circuit before, so Im trying to figure out where this linear regulator would be :)

AntonK

[Zbig]

I'm talking about nominal voltage supplied to sensor from FMA FS8 Copilot, not about sensor itself.

[AntonK]

Interesting. I wonder if there is a resistor change on the board to change the gain on this board verses the traditional set that works on 5V. Good information anyways.

AntonK