multiple Adc simultaneously

[sahu77]

How can I use multiple (three) adc simultaneously.
1st adc for input sense.
2nd adc for output sense.
3rd adc for overload sense.

When 3rd adc (overload) sense, mcu wait 10 min, after 10 min if 3rd adc (overload) sense now then it will go over load cut off case, otherwise stay current case.

In this 10 min if 2nd adc (output) sense high volt it will go hi cut off case, otherwise stay current case.

& also in this 10 min 1st adc (input) sense it will work as i define for its function.

ADC sense as

[temtronic]

First, No PIC can simultaneously read 3 ADC channels, but that's not your real problem, just a language thing...

Second this is not a complete program so I can't comment on the 'flow' or logic, or HOW you've assigned variables.

Comments...

1) You should use 'real names' for the variables like Input_sense, Output_sense, Overload_Sense as CH_3 doesn't make me think of 'overload' reading.

2)Your actual reading an ADC channel and getting the average reading is very poorly written. I'd suggest using say take 8 readings , then average those. Very fast for the compiler to cut efficient code.

3) You don't say whether the ADC is in 8 bit or 10 bit mode.

4) your 'if statement logic for all conditions is very,very 'messy' and almost impossible to follow. I suggest you delete everything and start all over. Create code to read and display the raw ADC values,either to LCD or PC, to confirm the numbers you're getting are correct

Then add code (switch statement logic or simple if...then ..else ) for each condition, ONE condition , at a time. It will be cleaner and easier to follow,especially to check for mistakes in logic !


You should ALWAYS include PIC type and Compiler version.There are some known issues that we may spot given this data.

You need some kind of real time clock interrupt for your program. There's a nice software RTC in the code library, easy to follow, easy to use, a good choice for your program.

[SherpaDoug]

A couple more suggestions;

1) Read_adc() automatically waits for the A/D to finish conversion. You rarely if ever need to use adc_done().

2) Use select case instead of all those if() statements.

3) Look up "Olympic Average" on this forum for a simple fast way to average A/D readings and get rid of outlyers. At least make sure your ADC_AVERAGE_COUNT is a power of 2 so the division is easy.

4) tlong is declared as int32 so you should cast it to int16 before returning.
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[sahu77]

[sahu77]

[SherpaDoug]

Consider this code:

[sahu77]

now

[SherpaDoug]

[sahu77]

which right ?
this

[SherpaDoug]

This line will not work:

tlong = (int16)ADC_value*5000; //Convert the result in millivolts

If ADC_value has the value 100 then 100 * 5000 will not fit a an int16 so it will be clipped and the accuracy lost. The PIC must first evaluate the right side of the equation before it assigns it to tlong. As ADC-value is not declared I would use:

tlong = (int32)itemp * 5000; //Convert the result in millivolts

The part (int32)itemp tells the compiler to use int32 size math for the multiplication.


This line:

return (int16) tlong; // cast result to fit return size

makes sure the int32 size tlong is properly converted to int16 size before it is returned from the function. The compiler will probably convert it automatically, but if it does not the bug could be very hard to find. It also might confuse someone else reading your code years from now.
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[sahu77]

Thanks for reply. But my 2nd question is rest. How can I set AN0, AN1, AN3 ?
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sahu

[SherpaDoug]

How about this:

[Brandon03]

there is a way to do true simultaneous sampling. It onvolves using many discrete Sample and Hold circuits. You just connect S/h input to your signals, outputs to analog pins of PIC and tie all of write strobe pins together to single pin of PIC. This way you can trigger many samplings at exactly the same time and then digitalize them one by one with ADC.

[RF_Developer]

[SherpaDoug]

To achieve simultaneous sampling you could try several ways.

1) Brandon03 describes how to do it with external hardware.
2) You could use several small PICs, one for each input and synchronize them.
3) If you are averaging anyway, you could interleave the channels in the averaging loop. It is not true simultaneous sampling but pretty close.

Sample 1 channel A
Sample 1 channel B
Sample 1 channel C
Sample 2 channel A
Sample 2 channel B
Sample 2 channel C
.
.
.
Sample N channel A
Sample N channel B
Sample N channel C

Then average the N samples for each channel.
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The search for better is endless. Instead simply find very good and get the job done.