Infrared Sensors

Paparazzi x-y IR sensor board

The paparazzi autopilot uses infrared thermopiles for primary attitude sensing. The theory is that at zero bank or pitch angle, the difference in the heat between the two sensors should be zero, and at 90 degrees it should be maximum. From this relationship a linear regression is made and angles are calculated during flight. Each pair of sensors measures one axis, a minimum of 2 pairs must be used to measure pitch and roll but best results are obtained thru the use of a 3^rd pair on the vertical axis. Since the output signal from each sensor pair is proportional to both the attitude and the weather/terrain, systems with only x-y sensors require a ground calibration and may not provide accurate angle calculations as the aircraft travels over terrain with different IR radiation.

Architecture

Dual Axis Board Pinout

Component Side View

Pin #	Name	Notes	Suggested Color
1	IR2	IR Signal Output Axis 2	Grey
2	GND	Ground	Black
3	VCC	+3.3v Power Supply	Red
4	IR1	IR Signal Output Axis 1	Braun

Single Axis Board Pinout

Component Side View

Pin #	Name	Notes	Suggested Color
1	IR	IR Signal Output	Purple
2	VCC	+3.3v Power Supply	Red
3	GND	Ground	Black

Below is a product designed by FMA Direct and is a replacement for their Flight Stabilization system. With a simple resistor swap, this module is suitable for use in the Paparazzi UAV.

CPD4SENUNIT

Parts

The Thermopiles are:

Manufacturer Part Number: MLX90247-ESF-DSA (Digi-Key: MLX90247-ESF-DSA-ND)

Description: IC SENS THERMOPILE W/THERM TO-39

FMA Direct CoPilot Sensor Head

IR Sensor Board Bottom

IR Sensor Board Top

Stock FMA Components

The stock FMA resistors R2/R3 and R5/R6 (0603 0.8 Mohm/0603 510 ohm) set the op amp gain to approximately 1600. Since this unit is designed to run on 5V and we are running it on 3.3V, it is advised to change R3 and R6 from 510 ohm to 1K ohm for an approximate gain of approximately 800. Without the change, it is theoretically possible to overdrive the Op Amp in extreme hot regions/seasons.

Another resistor swap option for this board is to replace R2 and R5 with 560 Kohm resistors, generating an output gain of approximately 1100; a gain which is practically identical to that of the Paparazzi board.

a suitable resistor from mouser is here

R1	200 ohm
R2	0.8 Mohm
R3	510 ohm
R4	200 ohm
R5	0.8 Mohm
R6	510 ohm
R7	600 ohm
R8	600 ohm
C1	0.026 uF
C2	0.026 uF
C3	0.026 uF
C4	0.026 uF
C5	0.01 uF
C6	0.026 uF

FMA Direct Vertical Sensor

IR Vertical Sensor Board Bottom

IR Vertical Sensor Board Top

The same operation can be done with the vertical sensor (single axis). The resistor R3 should be changed from a 510 ohm to a 1K ohm.

a suitable resistor from mouser is here