Low-Power Control Systems

Thoughts on processing Arduino analog pin output to read and properly format AttoPilot sensor data

AttoPilot's Specifications 63.69mV/Volt

36.60mV/Amp

My Calculations Assuming Arduino’s 5V ADC in use:

5V (max Arduino input) = 1023

3.3V (max AttoPilot output) = 675.18

AttoPilot 0V when measuring current = 0A

AttoPilot 0V when measuring voltage = -0.3V

3.3V = 675.18 = 90.15 Amps = 60 Volts

Measuring Current

Adjustment factor for Amps = 90.15/675.18 = 0.13351995 = 0.13 (for Arduino two decimal place float)

Measuring Voltage

An issue with measuring voltage with the AttoPilot is that the AttoPilot measures voltage from -0.3V to 60V.

Adjustment factor for Volts = (60 + 0.3) (to account for 0 = -0.3 and determine the AttoPilot's measured voltage range) = 60.3/675.18 = 0.089309517 = 0.09 (for Arduino two decimal place float)

Determine 0V point in AttoPilot's Output 0.3V / 0.089309517 = 3.359104495 = 0V

Worked Cases - Psuedo-code

if measured val > 3.36 
voltage is positive

60V = (675.18 – 3.36) = 671.82

Find the factor:

60V / 671.82 = 0.089309637

Taking the half-way case:

(671.82 / 2 ) = 335.91

335.91 * 0.089309637 = 30V

elsif measured val < 3.36)
voltage is negative

Taking the half way case:

0 = -0.3V

1.68 = -0.16V theoretically

1.68 * 0.089309637 = (0.15004019 * -0.1)

elseif (measured val = 3.36)
voltage is zero

Having gone gone through this, I suspect there is a more accurate method using unsigned longs rather than floats. Perhaps along the lines of:

http://www.openobject.org/opensourceurbanism/Counting_Revolutions#Calculating_Distance_and_Speed