Analog Schmartboards
Ian Knight
Lionschasing .
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Ian Knight
Ok Archie how can I help?
First question is are these sensors Analogue or Digital?
If Digital it is simply a matter of programming/coding the Arduino IC2 or SPI ports to talk to the device. OScope is very useful for debugging the conversation.
If Analogue it is an Arduino Analogue to Digital converter job, reading samples and turning it into values that represent what measurement you want. (This may require calibration)
One issues is sensitivity e.g thermocouple might work over range of -100c to +200c and as you may only be interested in say 20c to 50c so you may not get the resolution you require with an 8bit A/D conversion. So you may simply want to add an Op amp in with a couple of bias resistors to amplify the mid range to give you required resolution and what falls below or above the boundaries is out of rang data and of no consequence.
I have not programmed Ardunio but have done quite a bit of A/D and IC2/SPI in PIc24 and DsPIC so lot of code if you want to take and HACK.
Also remember back to old PHS when we where sorting out what to keep and junk. Well we had some Rabbit 8bit microcontrollers I had donated, that got passed on to Stephen. There is lot of code there i wrote to drive the A/D and a serial display that maybe of some use if Stephen still has them.
Ian
Lionschasing .
Ian Knight
Archie,
If you are familiar with writing micro controller code then ignore the rest of this post.
If not that familiar then the following may be of interest and reap many rewards as the programme grows.
A big no no is using delay of wait to wait for i/o send/receive/status etc functions as they change the latency of the programme:
One: if you change the environment (different chip or i/o speed) you may have to go back and change the duration of the delay/wait function.
Two generally if you use more than ONE delay or wait function they can interact with each other so you have to tune two or more areas of your code.
What I find works best for me is to have a TIMER based interrupt handler that uses a state counter to controller the i/o and to use Main() to do the overall control of what your trying to do.
AND DON’T FORGET Volatile! Doing so will really mess up your head.
You can if you want to get real cleaver is to replace the while loop with a SLEEP to put the cpu in hibernation and when the i/o completes the timer function wakes up to cpu to do main()…. Save this for version two or three.
Something like this:
Volatile int DataReady;
Volatile int NewData;
Volatile OneSecond;
Main()
{
Volatile Int MyData;
DoInitialization(); // Setup io port etc
StartOmsMSTimer(); // This starts a 1ms timer that generates an interrupt
While(1)
{ // loop forever
If( IO_StateCounter == FALSE )
IO_StateCounter = TRUE; Start the receive.. but let the interrupt handler do all the work.
If(DataReady)
{
DataReady--;
MyData = NewData; // Capture new data
Process MyData….Blah…Blah
}
If(OneSecond) // use this to keep track of things that main() needs to do… there maybe some timing jitter but generally good enough for most applications.
{
OneSecond = FALSE;
}
} // end loop forever
} // end main…………………….
Int MS_COUNTER;
Int IO_StateCounter;
Interrupt StartOmsMSTimer() // This function is called by an interrupt ever millisecond
{
MS_COUNTER++;
If( MS_COUNTER >= 1000 )
{
MS_COUNTER = 0;
OneSecond = TRUE; // Use 1 second counter.. use something like this to control flow of main()
}
Switch( IO_StateCounter )
{
Case START_IO;
///….Do whatever
Break;
Case IO_READY;
////…. Start Receiving….
Break;
Case IO_COMPLETE
////….Receive complete so tell main have some data;
NewData = GetReceiveData();
DataReady++;
StopIO();
Break;
}
// RESET Interrupt flag…
} // end 1ms interrupt
Ian Knight
Archie,
Another good tip when micro controller programming is to define some io ports as digital out and put an LED on them.
Call em test led 1 thru 8 say.
Then in the code toggle the bit to signal that this area of code has been called..
Thus TEST_LED_1 ^= 1; \\ toggle test led 1
Ian Knight
Archie,
Sorry the below could cause problem if timer goes off again before you have read NewData in Main():
If(DataReady)
{
DataReady--;
MyData = NewData; // Capture new data
Process MyData….Blah…Blah
}
Better like this:
If(DataReady)
{
MyData = NewData; // Capture new data
DataReady--; // reset flag
Process MyData….Blah…Blah