Math operations execution time

[Dave]

One question I have is, How do you have the pressure sensor mounted? If it mounted in such way that the thrust is being impressed on the sensing element then the pressure readings will be offset. I would mount the sensor so that the sensing element is perpindicular to the rockets thrust. It should give you a much more stable and reliable reading. I would also take about 64 readings and do a right shift 4 places to the give you a 12 bit reading. I do this as a mater of fact for all of my A/D readings from the PIC internal A/D. I only use a 40uS. delay when changing channels. You should easily be able to captute the data at 100 Hz.

[rasciodc]

One question I have is, How do you have the pressure sensor mounted? If it mounted in such way that the thrust is being impressed on the sensing element then the pressure readings will be offset. I would mount the sensor so that the sensing element is perpindicular to the rockets thrust. It should give you a much more stable and reliable reading. I would also take about 64 readings and do a right shift 4 places to the give you a 12 bit reading. I do this as a mater of fact for all of my A/D readings from the PIC internal A/D. I only use a 40uS. delay when changing channels. You should easily be able to captute the data at 100 Hz.

Yes Dave, you´re right! I still have to think about how the circuit will be disposed inside the rocket, calculate the pressure vents in the fuselage and etc...
Anyway, as I said, I am very noob to this so, is there any material where I can read about this 12bit reading with a 10bit AD?

[spcw1234]

I would also take about 64 readings and do a right shift 4 places to the give you a 12 bit reading. I do this as a mater of fact for all of my A/D readings from the PIC internal A/D. I only use a 40uS. delay when changing channels. You should easily be able to captute the data at 100 Hz.

Can you explain this in more detail? Sounds like an interesting trick to me. Thanks!

[Dave]

Just accumulate 64, 10 bit readings in a row into the same word variable, then do a shift to the right by 4 places which will give you a 12 bit result. Here is an example:
'************************************************* ********************
READAD: 'READ SYSTEM A/D VOLTAGES (AVERAGE 64 READINGS) 18F2620
'************************************************* ********************
TMPCHAN = CHANNEL 'COPY CHANNEL DATA
IF CHANNEL = 3 THEN TMPCHAN = 4 'SKIP CHANNEL 3 AS IT IS USED AS REFERENCE
ADCON0 = $01 | (TMPCHAN << 2) ' Set A/D to Channel X, On
PAUSEUS 40
VOLTS(CHANNEL) = 0 'CLEAR A/D READINGS
SCRATCH = 0
WHILE SCRATCH < 64 'SUM 64 READINGS
ADCON0.1 = 1 ' START CONVERSION
WHILE ADCON0.1 = 1 'WAIT FOR A/D TO FINISH
WEND
VOLTS(CHANNEL) = VOLTS(CHANNEL) + (((ADRESH & $3) << 8) + ADRESL) 'BUILD SENSOR WORD
SCRATCH = SCRATCH + 1
WEND
VOLTS(CHANNEL) = VOLTS(CHANNEL) >> 4 'TURN INTO 12 BIT RESULT

RETURN

[gadelhas]

Hi;

Following what Dave has said, take a look at this link, by Darrel Taylor;
http://www.darreltaylor.com/DT_Analog/

By the way rasciodc, i'm Portuguese too, i'm from Maia.

[spcw1234]

Thank you Dave, and Gadelhas! I am excited to try this!

[rasciodc]

Hi;

Following what Dave has said, take a look at this link, by Darrel Taylor;
http://www.darreltaylor.com/DT_Analog/

By the way rasciodc, i'm Portuguese too, i'm from Maia.

Thanks, gadelhas, for the link! very useful!! mainly for beginners like me!
And, actually I´m Brazilian! living in São Paulo at the time....

Just accumulate 64, 10 bit readings in a row into the same word variable, then do a shift to the right by 4 places which will give you a 12 bit result.

Dave, thanks for the explanation! How much time would this algorithm take to do this, any idea? (just wondering if I can use it in my altimeter...)
Thanks!

[amgen]

Isn't the 12-14-16 bit reading just a guess about being between the 2- 10 bit readings which could be off the expanded factor bits ??
If the a/d values do not bounce in the 64 samples, the actual voltage could be up or down on that step but the guess would be middle.
Don
amgen

[ScaleRobotics]

If the a/d values do not bounce in the 64 samples, the actual voltage could be up or down on that step but the guess would be middle.

Yes, but in practice the numbers jump around enough so oversampling can extract more data from the result. The main drawback is speed, but it is very effective.

Here's some sources of info:
http://www.atmel.com/dyn/resources/p...ts/doc8003.pdf
http://ww1.microchip.com/downloads/e...otes/Achieving Higher ADC Resolution Using Oversampling 01152A.pdf