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PIC18F2585 using Accelerometer Interrupts

 
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skeinath



Joined: 05 Aug 2019
Posts: 1

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PIC18F2585 using Accelerometer Interrupts
PostPosted: Mon Sep 30, 2019 2:04 pm     Reply with quote
I have a custom board with PIC18F2585, an RGB LED, and an lis3dh accelerometer.

I am trying to use the accelerometer as an interrupt to wake up the PIC.

Can someone create a simple sample project that sets the accelerometer to wake up the PIC when the board is moved?... and ideally, it would put the PIC back to sleep if it hasn't moved in N number of seconds (30)? While the PIC is awake, turn on the green LED (on = output_low).

I've read the datasheets, tried a few times, and am still lost. Sorry... I am still a beginner to embedded, especially interrupts.


R - RC0 (11)
G - RC1 (12)
B - RC2 (13)
SCL - RC3 (14)
SDA - RC4 (15)
ACCL Int 1 - RB1/INT1/AN8 (22)
ACCL Int 2 - RB2/INT2 (23)



Thank you so much in advance,
Steve
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Sep 30, 2019 4:49 pm     Reply with quote
See this post by newguy. He uses the accelerometer interrupt to set a
flag, which tells his main loop to clear the flag, read the accelerometer,
do some calculations, and then display the results on an lcd.
http://www.ccsinfo.com/forum/viewtopic.php?t=51309&start=1
benoitstjean



Joined: 30 Oct 2007
Posts: 566
Location: Ottawa, Ontario, Canada

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PostPosted: Mon Sep 30, 2019 7:46 pm     Reply with quote
Hi Steve,

First, whatever you posted in your message is not useful at all. You also haven't posted any code nor your compiler version etc.

Second, if I was you I would make the simplest of all circuits using only an LED and a pushbutton.

In a while loop, just read the pushbutton and everytime it is high, turn-on the LED and when low, turn it off.

When that works, next step is to test with the interrupts.

Configure the PIC so that the input for the pushbutton is set to run as an external interrupt and when you push that button, then the LED turns-on, wait 2 seconds then turn-off.

I am using the ADXL345 accelerometer from Analog Devices and I'm using it like you are in a sense that after so many minutes, the entire circuit shuts-down and if I tap the circuit, then the circuit wakes-up.

However, considering you specified you are a beginner in embedded and whatever you posted does not provide any value for anyone to help you, there's not much we can do here and what you want to accomplish is not as simple as it sounds especially if you're a beginner.

You have to be realistic. The accelerometer has a bunch of registers that need to be configured over I2C (or SPI) therefore the learning curve might be somewhat of a challenge if you've never programmed with the PIC before and can't get a simple interrupt to work.


Interrupts are easy, it's just a matter of enabling the interrupt like this:

Code:

#define INT_EXT1 PIN_x  where 'x' is the pin ID (e.g. PIN_D5) -- Check the PIC datasheet
#define LED  PIN_y where 'y' is another PIN ID like above

Then you need the interrupt function like below:
Code:

#INT_EXT1
void INT_EXT_INPUT1( void )
{
    output_pin( LED, 1 );  // Turn-on the LED
    delay_ms( 2000 );  // Wait 2 seconds
    output_pin( LED, 0 ); // Turn-off the LED
}

main()
{
   enable_interrupts( INT_EXT1 );  // Enable external interrupt 1
   ext_int_edge( 1, H_TO_L );    // Set the interrupt to trigger on a High-to-Low transition
   enable_interrupts( GLOBAL );    // Enable global interrupts

   while( 1 );
}

Note that the code above is just to show the most basic steps... there's a LOT more to the above that is required such as fuse configuration, oscillator configuration etc.

Anyhow, start with the LED and pushbutton and when you get that to work, you will then need to figure-out how to talk to the accelerometer over I2C/SPI and when that works, then you will be able to do more.

You also need to know electronics and how to interface between the PIC and accelerometer because they may not be at the same voltages. You may also not want to drive the LED directly from the PIC output either.

Bottom line: go baby steps, one thing at a time. When one step works, proceed to the next.

That accelerometer has two interrupt outputs, one that goes high when motion is detected and one that goes high when the detected motion has stopped. It can probably do a million other things.

You will also need to provide a bit of meat to show the work you have done on your side.

Good luck.

Ben
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