Start off by using the formula:

y = mx-b

where

y = output Volts

m = slope

x = input units

b = offset

Let's use a pressure sensor that has a range of 0 psi to 100 psi, with 1 volt output equaling 0 psi and 5 volts equaling 100 psi.

m = slope

There is a 4 volt span. psi/volt 100/4 = 25

m = 25

x = input units

This is the output from the sensor, in this case it will be between 1 and 5.

b = offset

Since the output starts at 1 volt, there is an offset. We calculated a value of 25 psi/volt.

b = 25

Plug all this into the formula and lets say the input is 5.0 volts.(full scale)

y = (25 * 5) - 25

y = 100 psi

Convert this to an 8 bit PIC® resolution.

8bits ADC = 0 to 255, 256 steps.

At 5.0 volts one volt of input will will read 51.

New value for "m"

Spanning 4 volts or 204 steps (4 * 51).

100 / 204 = 0.49

m = 0.49

New value for "b"

The new offset starting at 51, (1 * 51).

51* 0.49 = 24.99

b = 24.99

ADC is from the sensor.

ADC = 255 Full scale

y = (ADC * 0.49) - 24.99

y = 99.96 psi

#############

Convert this to an 10 bit PIC® resolution.

10 bits ADC = 0 to 1023, 1024 steps.

At 5.0 volts one volt of input will will read 204. (204.8 actually)

But we will use 205 for accuracy.

204 * 5 = 1020

205 * 5 = 1025

New value for "m"

Spanning 4 volts or 820 steps (4 * 205).

100 / 820 = 0.1219

m = 0.1219

New value for "b"

The new offset starting at 205, (1 * 205).

205 * 0.1219 = 24.9

b = 24.9

ADC is from the sensor.

ADC = 1023 Full scale

y = (ADC * 0.1219) - 24.9

y = 99.8 psi

Now for some code. You will see some rounding for integer math.

8 bit

' m = 0.49 ' b = 24.99 ' y = (ADC * 0.49) - 24.99 ' ADC = 255 ' y = 99.96 M CON 49 'm = 0.49 * 100 B CON 24 'b = 24.99 ADC VAR WORD 'INPUT FROM SENSOR Y VAR WORD 'PSI Z VAR WORD 'DUMMY VAR Z1 VAR WORD 'DUMMY VAR START: ADC = 255 'FULL SCALE HARD CODED, NO SENSOR Z = ADC * M Z1 = DIV32 100 Y = Z1 - B LCDOUT $FE,1,"PSI= ",DEC Y PAUSE 250 GOTO START

' m = 0.1219 ' b = 24.9 ' y = (ADC * 0.1219) - 24.9 ' ADC = 1023 ' y = 99.8 M CON 1219 'm = 0.1219 * 10,000 B CON 249 'b = 24.9 * 10 ADC VAR WORD 'INPUT FROM SENSOR Y VAR WORD 'PSI Z VAR WORD 'DUMMY VAR Z1 VAR WORD 'DUMMY VAR START: ADC = 1023 'FULL SCALE HARD CODED, NO SENSOR Z = ADC * M Z1 = DIV32 1000 Y = Z1 - B LCDOUT $FE,1,"PSI= ",DEC Y/10,".",DEC2 Y//100 PAUSE 250 GOTO START

## Re: PIC USB HID breakout board

Sorry, that question was for amgen

towlerg Today, 00:03