Problem with MMA7455 Accelerometer and SimpleIDE Terminal
amalfiCoast
Posts: 130
Hello,
I am using the MMA7455 3-Axis Accelerometer module (https://www.parallax.com/product/28526) on a Propeller Activity Board. I followed the SPI Example (http://learn.parallax.com/tutorials/language/propeller-c/propeller-c-simple-protocols/spi-example) and am using the provided code to take measurements on the z-axis. When I try to sample at 50Hz by changing the pause time from 500 to 20, the measurements in the SimpleIDE terminal cannot seem to keep up. The datasheet for the accelerometer says the chip can sample at up to 125Hz and 250Hz, depending on the bandwidth setting. Is the Propeller or SimpleIDE terminal the limiting factor or is there something I am doing wrong?
Thanks,
David
I am using the MMA7455 3-Axis Accelerometer module (https://www.parallax.com/product/28526) on a Propeller Activity Board. I followed the SPI Example (http://learn.parallax.com/tutorials/language/propeller-c/propeller-c-simple-protocols/spi-example) and am using the provided code to take measurements on the z-axis. When I try to sample at 50Hz by changing the pause time from 500 to 20, the measurements in the SimpleIDE terminal cannot seem to keep up. The datasheet for the accelerometer says the chip can sample at up to 125Hz and 250Hz, depending on the bandwidth setting. Is the Propeller or SimpleIDE terminal the limiting factor or is there something I am doing wrong?
Thanks,
David
Comments
We can attempt to answer this, but I think we'll need to see your code. The terminal in SimpleIDE should be able to handle this, the UART library for communicating with the terminal shouldn't be having any issues, and the SPI library from communicating with your accelerometer shouldn't have any issues. Something seems off to me.
Thanks for your response. Here is my code:
/*
MMA7455 Test Z Axis.c
*/
#include "simpletools.h" // Include simpletools lib
signed char z; // Z-axis value
int main() // Main function
{
high(6); // CS line high (inactive)
low(8); // CLK line low
low(6); // CS -> low start SPI
shift_out(7, 8, MSBFIRST, 7, 0b1010110); // Write MCTL register
shift_out(7, 8, MSBFIRST, 1, 0b0); // Send don't-care bit
shift_out(7, 8, MSBFIRST, 8, 0b01100101); // Value for MCTL register
high(6); // CS -> high stop SPI
pause(1);
while(1) // Main loop
{
low(6); // CS low selects chip
shift_out(7, 8, MSBFIRST, 7, 0b0001000); // Send read register address
shift_out(7, 8, MSBFIRST, 1, 0b0); // Send don't-care value
z = shift_in(7, 8, MSBPRE, 8); // Get value from register
high(6); // De-select chip
print("%c z = %d%c", HOME, z, CLREOL); // Display measurement
pause(500); // Wait 0.5 s before repeat
}
}
When I change pause(500) to pause(20) the SimpleIDE terminal cannot keep up and shows significant lag (5-10 sec). However, if you use pause(30) or higher, it seems to work fine.
Thanks,
David
Also, next time you might use the [ code ] tags. Or highlight your code and press the "C" button at the top of the text editor.
I'll try running your code when I get home and see if I can recreate your issue.
with just 20ms you send data faster as the output can send it to the terminal.
At what baud rate you send/receive to the terminal?
Enjoy!
Mike
Sorry about that - here is the code with the tags:
/* MMA7455 Test Z Axis.c */ #include "simpletools.h" // Include simpletools lib signed char z; // Z-axis value int main() // Main function { high(6); // CS line high (inactive) low(8); // CLK line low low(6); // CS -> low start SPI shift_out(7, 8, MSBFIRST, 7, 0b1010110); // Write MCTL register shift_out(7, 8, MSBFIRST, 1, 0b0); // Send don't-care bit shift_out(7, 8, MSBFIRST, 8, 0b01100101); // Value for MCTL register high(6); // CS -> high stop SPI pause(1); while(1) // Main loop { low(6); // CS low selects chip shift_out(7, 8, MSBFIRST, 7, 0b0001000); // Send read register address shift_out(7, 8, MSBFIRST, 1, 0b0); // Send don't-care value z = shift_in(7, 8, MSBPRE, 8); // Get value from register high(6); // De-select chip print("%c z = %d%c", HOME, z, CLREOL); // Display measurement pause(500); // Wait 0.5 s before repeat } }I am not sure how to check for the memory model but I am using the stock SimpleIDE configuration.
Mike:
I am using the 115200 baud rate.
Thanks,
David
SimpleIDE in its default configuration with this code and the print function will run unbuffered serial comms. That means you can't overflow the buffer on the Propeller side.
Also, I booted ran this code and was not able to reproduce your issue. Can you please upload a full zip of your project using the menu Project -> Zip? Also, since I don't have a real MMA7455 accelerometer to plug in, I faked it by modifying the code to include an index variable that is printed at the start of the line. Without it, it would just keep printing "z = 0"
/* MMA7455 Test Z Axis.c */ #include "simpletools.h" // Include simpletools lib signed char z; // Z-axis value int main() // Main function { high(6); // CS line high (inactive) low(8); // CLK line low low(6); // CS -> low start SPI shift_out(7, 8, MSBFIRST, 7, 0b1010110); // Write MCTL register shift_out(7, 8, MSBFIRST, 1, 0b0); // Send don't-care bit shift_out(7, 8, MSBFIRST, 8, 0b01100101); // Value for MCTL register high(6); // CS -> high stop SPI pause(1); int i = 0; while(1) // Main loop { low(6); // CS low selects chip shift_out(7, 8, MSBFIRST, 7, 0b0001000); // Send read register address shift_out(7, 8, MSBFIRST, 1, 0b0); // Send don't-care value z = shift_in(7, 8, MSBPRE, 8); // Get value from register high(6); // De-select chip print("%c%d z = %d%c", HOME, i++, z, CLREOL); // Display measurement pause(20); // Wait 0.5 s before repeat } }Hi,
I had the same issue with my primality program, which outputs the results very fast. Indeed, the SimpleIDE terminal doesn't keep up, showing intermittent blinking and omitting results in the process. I confirmed, both visually by the LEDs and using a scope, that the Activity Board was sending the results without interruption, and it was the terminal that was not updating properly. Seemingly, it is a buffering issue. My suggestion is to program to EEPROM and try using PuTTY to communicate. Worked like a charm for me.
Kind regards, Samuel Lourenço