Dimitris76
Jul 26, 2008, 04:50 PM
Hi all!
Here is my problem: I am using the thermopile sensor pack from the FMA's Co-pilot system for an OSD artificial horizon.
The firmware - as it is - supports only the + orientation of the sensors (sensor pairs along and perpendicular the fuselage) and NOT the X orientation (that has the sensors "looking" diagonally).
This sensor pack has a 4 pin connector: GND, Vref=3.3V, Pitch, Roll.
The thermopiles are coupled in pairs and their output is a voltage that variates from 0 to 3.3V, proportionally to the heatreading difference on each side. For example when the aircraft is flying level the voltage at the Roll output (V1) is 1.65V, when it's rolling left it's 0-1.65V and when it's rolling right 1.65-3.3V. Same for diving/climbing - the Pitch (V2) voltage variates according to the angle.
All these of course apply if the sensor is like I said mounted in the + mode and the thermopile pairs are looking front-aft, left-right...
After a lot of thinking and since modifying the firmware is not an option I came to the conclusion that an external circuit between the sensor pack and the OSD board needs to be constructed which will modify the voltages according to the following formulas:
V1'= (V1+V2)/2 and V2'=(Vref+V1-V2)/2
where V1' and V2' should be the voltage pairs on the diagonal mode.
And the circuit that I designed is this:
http://i12.photobucket.com/albums/a235/Dimitris76/MAHIopamps-1.jpg
All the resistors are 100k except the voltage divider ones that are 10k.
In the schematic I used the LM741 OpAmplifier ICs that I found in Eagle's library, and since these OpAmps have a maximum output voltage Vcc-1.5 volts I need +5V at the supply rail in order to get 3.3v at full angle deflection.
Mr-Cam suggested that if I use a rail-to-rail OpAmp I could omit this 5V supply and power the amplifier straight from the 3.3V Vref.
So, I searched and found this
http://www.elfa.se/pdf/73/734/07345945.pdf
dual CMOS rail-to-rail OpAmp that I "think" it might be up to the task... What do you guys think? Does the circuit look OK? Do you have another OpAmp or resistor values to suggest?
Dimitris
Here is my problem: I am using the thermopile sensor pack from the FMA's Co-pilot system for an OSD artificial horizon.
The firmware - as it is - supports only the + orientation of the sensors (sensor pairs along and perpendicular the fuselage) and NOT the X orientation (that has the sensors "looking" diagonally).
This sensor pack has a 4 pin connector: GND, Vref=3.3V, Pitch, Roll.
The thermopiles are coupled in pairs and their output is a voltage that variates from 0 to 3.3V, proportionally to the heatreading difference on each side. For example when the aircraft is flying level the voltage at the Roll output (V1) is 1.65V, when it's rolling left it's 0-1.65V and when it's rolling right 1.65-3.3V. Same for diving/climbing - the Pitch (V2) voltage variates according to the angle.
All these of course apply if the sensor is like I said mounted in the + mode and the thermopile pairs are looking front-aft, left-right...
After a lot of thinking and since modifying the firmware is not an option I came to the conclusion that an external circuit between the sensor pack and the OSD board needs to be constructed which will modify the voltages according to the following formulas:
V1'= (V1+V2)/2 and V2'=(Vref+V1-V2)/2
where V1' and V2' should be the voltage pairs on the diagonal mode.
And the circuit that I designed is this:
http://i12.photobucket.com/albums/a235/Dimitris76/MAHIopamps-1.jpg
All the resistors are 100k except the voltage divider ones that are 10k.
In the schematic I used the LM741 OpAmplifier ICs that I found in Eagle's library, and since these OpAmps have a maximum output voltage Vcc-1.5 volts I need +5V at the supply rail in order to get 3.3v at full angle deflection.
Mr-Cam suggested that if I use a rail-to-rail OpAmp I could omit this 5V supply and power the amplifier straight from the 3.3V Vref.
So, I searched and found this
http://www.elfa.se/pdf/73/734/07345945.pdf
dual CMOS rail-to-rail OpAmp that I "think" it might be up to the task... What do you guys think? Does the circuit look OK? Do you have another OpAmp or resistor values to suggest?
Dimitris