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benoitstjean
Joined: 30 Oct 2007
Posts: 543
Location: Ottawa, Ontario, Canada
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| MPL3115 code for PIC24? [WORKS - CLOSED] |
 Posted: Thu Oct 29, 2020 9:47 pm |
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Device: PIC24EP512GP806
Compiler: 5.026
Hi guys,
Anyone has simple working code for the MPL3115A2 pressure sensor from NXP in polling altimeter mode? I wrote some code that somewhat works but I'd like to compare with other known working code. I find that the values returned, even when polling every second, swing a lot, perhaps a bit too much for my taste. I was expecting to see something much more stable but it seems that the altitude, just sitting there, swings by 1-2 feet, sometimes even more. I'm curious to test other code.
I may have to contact NXP for support, I'll also check on their support page.
| Code: |
typedef struct
{
unsigned int8 AltitudeIntegerMSB;
unsigned int8 AltitudeIntegerCSB;
unsigned int8 AltitudeIntegerLSB;
float fAltitude;
unsigned int8 ID;
} SALTIMETER;
SALTIMETER ALT;
//-------------------------------------
unsigned int8 ALT_Initialize( unsigned int8 MsgID )
{
ALT.ID = PROTOCOL_Read_I2C( 0xC0, 0x0C );
delay_ms( 10 );
if( ALT.ID == ALT_MANUFACTURER_ID )
{
ALT.IsInitialized = TRUE;
return( TRUE );
}
ALT.ID = 0;
return( FALSE );
ALT.Register = PROTOCOL_Read_I2C( 0xC0, ALT_CTRL_REG1 );
ALT.Register = ALT.Register | 0x80;
PROTOCOL_Write_I2C( 0xC0, ALT_CTRL_REG1, ALT.Register );
delay_ms( 10 );
// Set oversample rate
ALT.Register = PROTOCOL_Read_I2C( 0xC0, ALT_CTRL_REG1 );
ALT.Register = ALT.Register | 0x38; // xx111xxx -> 128
PROTOCOL_Write_I2C( 0xC0, ALT_CTRL_REG1, ALT.Register );
// Enable event flags
PROTOCOL_Write_I2C( 0xC0, ALT_PT_DATA_CFG, 0x07 );
delay_ms( 10 );
return( ALT.ID );
}
//-------------------------------------
void ALT_ToggleOneShot( void )
{
// Clear OST bit
ALT.Register = PROTOCOL_Read_I2C( 0xC0, ALT_CTRL_REG1 );
ALT.Register = ALT.Register & 0xFD; // Force OSD bit to 0
PROTOCOL_Write_I2C( 0xC0, ALT_CTRL_REG1, ALT.Register );
// Set OST bit
ALT.Register = PROTOCOL_Read_I2C( 0xC0, ALT_CTRL_REG1 );
ALT.Register = ALT.Register | 0x02; // Force OSD bit to 1
PROTOCOL_Write_I2C( 0xC0, ALT_CTRL_REG1, ALT.Register );
}
//-------------------------------------
void ALT_ReadAltitude( void )
{
ALT_ToggleOneShot();
// Read altimeter PDR flag
while(( PROTOCOL_Read_I2C( 0xC0, ALT_STATUS ) & 0x04 ) == 0x00 )
{
// Here, have a counter that will exit if so many milliseconds have elapsed
}
//-----------------------------------------
// Altitude
//-----------------------------------------
// OUT_P_MSB: Contains integer MSB part in meters
// OUT_P_CSB: Contains integer LSB part in meters
// OUT_P_LSB: Contains fractional part
ALT.AltitudeIntegerMSB = PROTOCOL_Read_I2C( 0xC0, ALT_OUT_P_MSB );
delay_ms( 10 );
ALT.AltitudeIntegerCSB = PROTOCOL_Read_I2C( 0xC0, ALT_OUT_P_CSB );
delay_ms( 10 );
ALT.AltitudeIntegerLSB = PROTOCOL_Read_I2C( 0xC0, ALT_OUT_P_LSB );
delay_ms( 10 );
ALT.fAltitude = ((float) (( ALT.AltitudeIntegerMSB << 8 ) | ALT.AltitudeIntegerCSB )) + ((float) (ALT.AltitudeIntegerLSB >> 4) * 0.0625 );
//-----------------------------------------
// Temperature
//-----------------------------------------
// Read temperature integer
ALT.TemperatureMSB = PROTOCOL_Read_I2C( 0xC0, ALT_OUT_T_MSB );
// Read temperature decimals
ALT.TemperatureLSB = PROTOCOL_Read_I2C( 0xC0, ALT_OUT_T_LSB );
// OUT_T_MSB: Contains the integer part in °C
// OUT_T_LSB: Contains the fractional part
// Left shift OUT_T_MSB byte by 8 bits into a 16-bit variable and
// bitwise-OR OUT_T_LSB byte to give the temperature in °C, times 256.
// Adjust 4-bit temperature decimals to reflect 1/16th steps
ALT.Temperature = ALT.TemperatureMSB << 8;
ALT.fTemperature = ( ALT.Temperature | ALT.TemperatureLSB ) / 256;
ALT_ToggleOneShot();
}
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With the code above, I have a 1 second timer getting the data and displaying it and this is the output which makes no sense (no, I am not in outer space):
Current altitude: 214405.3ft (65359.50m) -- Temperature: 32.0C
Current altitude: 214404.8ft (65359.37m) -- Temperature: 32.0C
Current altitude: 214404.4ft (65359.25m) -- Temperature: 32.0C
Current altitude: 214404.0ft (65359.12m) -- Temperature: 32.0C
Changing the types for AltitudeIntegerMSB/CSB/LSB from unsigned int8 to signed int8 returns the following which makes a bit more sense but I guess there's some error in there:
Current altitude: -579.8ft (-176.75m) -- Temperature: 31.0C
Current altitude: -578.7ft (-176.43m) -- Temperature: 31.0C
Current altitude: -581.6ft (-177.31m) -- Temperature: 31.0C
Current altitude: -581.4ft (-177.25m) -- Temperature: 31.0C
Current altitude: -579.6ft (-176.68m) -- Temperature: 31.0C
So it makes more sense but the swing is quite wide. First time I play around with an altimeter so I may have overlooked some configuration details.... Given that these things are calibrated at sea level, I'm not high, perhaps 200m or less above sea level in Ottawa, Canada. So I would have expected an approximate value of my altitude from sea level....
Good night. Bed time and thanks for any pointers. When I get something working I'll post it in the working code folder on the forum.
Thanks.
Ben
Ottawa, Canada
Last edited by benoitstjean on Sun Nov 29, 2020 8:36 am; edited 2 times in total |
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benoitstjean
Joined: 30 Oct 2007
Posts: 543
Location: Ottawa, Ontario, Canada
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| Posted: Sun Nov 29, 2020 8:31 am |
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Had forgotten about this post. Here's what I have that works in case anyone is interested... This sensor can do lots but this is good for me. I guess I had overlooked the 2's complement part.
in .h file:
| Code: |
unsigned int8 AltitudeIntegerMSB; // Integer MSB
unsigned int8 AltitudeIntegerCSB; // Integer CSB
unsigned int8 AltitudeIntegerLSB; // Integer LSB
float fAltitude; // Altitude samples
//----- Temperature parameters -----
unsigned int8 TemperatureMSB; // Temperature integer
unsigned int8 TemperatureLSB; // Temperature decimals 4-bit (1/16th steps)
float fTemperature;
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In .c file:
| Code: |
void Initialize_altimeter( void )
{
// Set in altimeter mode with OSR = 128
Write_I2C( 0xC0, 0x26, 0xB8 );
delay_ms( 10 );
// Enable event flags
Write_I2C( 0xC0, 0x13, 0x07 );
delay_ms( 10 );
// Set active
Write_I2C( 0xC0, 0x26, 0xB9 );
delay_ms( 10 );
}
void Read_altitude( void )
{
int32 Integer = 0;
// Read altimeter 'busy' flag
while(( Read_I2C( 0xC0, 0x00 ) & 0x08 ) != 0x08 )
{
// Add some means (e.g. timer) of exiting to prevent while loop from getting stuck here.
}
//--------- Altitude ---------
// Read MSB of altitude integer
AltitudeIntegerMSB = Read_I2C( 0xC0, 0x01 );
delay_ms( 10 );
// Read CSB of altitude integer
AltitudeIntegerCSB = Read_I2C( 0xC0, 0x02 );
delay_ms( 10 );
// Read LSB of altitude integer
AltitudeIntegerLSB = Read_I2C( 0xC0, 0x03 );
delay_ms( 10 );
// Encompass bytes in single value
Integer = (( int32 ) AltitudeIntegerMSB << 24 ) | (( int32 ) AltitudeIntegerCSB << 16 ) | (( int32 ) AltitudeIntegerLSB << 8 );
// Check if value is negative
if( AltitudeIntegerMSB > 0x7F )
{
// Perform 2's complement: invert all bits then add 1
Integer != Integer + 1;
}
// Divide by 65536 to get altitude
fAltitude = (float)Integer / 65536;
//-------- Temperature --------
// Read temperature integer
TemperatureMSB = Read_I2C( 0xC0, 0x04 );
delay_ms( 10 );
// Read temperature decimals
TemperatureLSB = Read_I2C( 0xC0, 0x05 );
delay_ms( 10 );
// Encompass bytes in single value
Integer = ((int32) TemperatureMSB << 8 ) | ((int32) TemperatureLSB );
// Check if value is negative
if( TemperatureMSB > 0x7F )
{
// Perform 2's complement.
Integer != Integer + 1;
}
// Divide by 256 to get temperature
fTemperature = (float) Integer / 256;
}
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Enjoy.
Ben |
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