Help with the conversion math

[HenrikOlsson]

Yeah, deja vu indeed....

Ed,
* The resolution of the ADC is 10 bits.
* It does not return a reading directly in Volts.
* Basically it takes the difference between Vref+ and VRef- and divides that by 1024 (2^10, the resolution of the ADC). Each "count" in the value is then "worth" that amount.

So, if VRef- is GND (0V) and VRef+ is 5V the difference between the two is 5V. Each "count" in the ADC result is then "worth" 5/1024=4.88mV.
If the ADC returns 745 the voltage at its input is 5/1024*745=3.638V

I can't make out anything from that datasheet, it's just garbage numbers when viewed on my machine. I managed to find this one. And, I'm guessing you've got the 7psi sensor, correct? If so then something like this might work. I have not tested it though so all bets are off....

Of course you need to configure pins etc as usual (!)

Accumulator VAR WORD
i VAR BYTE
ADResult VAR WORD

Accumulator = 0

Main:

For i = 0 to 39
  ADCIN 4, ADResult  
  Accumulator = Accumulator + ADResult
  PauseUs 500
NEXT

ADResult = Accumulator / 10   ' Psuedo 12bit resolution, ADResult is now 0-4092

' Sensor outputs 0.5V (ADResult=409 ) at 0psi (nominal)
' Sensor outputs 4.5V (ADResult=3683) at 7psi (nominal)

ADResult = ADResult - 409   ' Offset for zero output, ADResult is now 0 to 3274 for 0 to 7psi
ADResult = ADResult */ 547  ' Scale up, ADResult is now 0 to 6995 for 0 to 7psi 

' Display Pressure: x.xx psi
HSEROUT["Pressure: ", DEC ADResult/1000, ".", DEC2 ADResult//1000, "psi", 13]

PAUSE 1000

Goto Main

/Henrik.

[richard]

Yeah, deja vu indeed....


I can't make out anything from that datasheet, it's just garbage numbers when viewed on my machine.

/Henrik.

ditto for the pdf
do we have a 54A L07H2210 or a 54ALL07H2210 or a 54AL007H2210 or a 54A 007H2210 ?
they are all different animals and the 54ALxxx are 3.3v devices

[EarlyBird2]

PDF works for me.

The sensor is a 0.07 psi low voltage range with output from 0.5-4.5V

[richard]

that makes it a "54A L07H2210" not what was posted , its best to be sure

steve can you read the characteristics in the data sheet ,that what comes out garbled for me

[EarlyBird2]

'* Notes : For a 18F1320 and 54AL07H2210 *

was it not?

[richard]

this is what I mean

[HenrikOlsson]

Is this not a repeat of the left and right output justification as on the previous thread in Richard's link.

Yes, that's exactly what it is. The reason for the results have been covered in that thread but not a way to end up with a correct pressure reading - which is still kind of hit and miss since we need specific details no the actual sensor used.

/Henrik.

[EarlyBird2]

Is this not a repeat of the left and right output justification as on the previous thread in Richard's link.

7040 left justified is 110 right justified using Henrik's 4.88mV then

110*4.88/1000=0.5368 V

Or put another way 7040/64=110 which shifts the 10 bit left justified result 6 bits to the right making the result the same as a right justified result.