Re: ADS1115 Data read problem

Craig,

When you first start up the ADS1115, the conversion register is zero and remains zero until a conversion replaces it with a result.  So you probably have not really started continuous conversion mode.

A couple of things.  To start with, you need to make sure that you have set the register pointer to the correct location when communicating to the device.  Another thing to keep in mind is that all register communication is in two byte transfers....in other words all registers are 16-bit.  So what is the actual configuration setting that you are trying to use, ie are you trying to use the default setting 0x8583 or something else.  For example if you want the device to be in continuous mode, but keep the default settings for all other bits you need to write to the config register 0x8483, which changes bit 8 to a zero.

The device should now be in continous conversion mode, so to read out the data you need to write the pointer to the conversion register, then you need to read out the results.

Best regards,

Bob B

Hello Craig,

The user may set up the device in continuous mode or Power down single-shot mode by setting the appropiate configuration register.  Table 9 on page 18 of the datasheet shows the Config Register. Setting Bit[8] of the config register controls the conversion mode of the ADS1115:  As described on Page 19 setting this bit to 1 sets the device on Power-down single shot mode (default); setting it to 0 configures the device on continuous conversion mode.

The quick start guide description on page 11, provides a helpful example where the device is set to continuous conversion mode by sending three commands: writing to the config register(4 bytes), writing to the pointer register (2 bytes), and reading the conversion register (3 bytes).

--The user can pole the OS bit by reading the configuration register:

1) Send a command write to the pointer register:
First byte: I2C Address followed by a low write bit
Second byte: 0b00000001 (point to the config register)

2) Send a command to read the config register:
First byte: I2C address followed by high read/write bit
Second byte: ADS1115 response with the MSB of the config register
Third byte: ADS1115 response with the LSB of the config register

Where bit 15 is the OS bit.

-- After reading that the OS bit = 1, you may read the conversion result:

1)Send a command to write to the pointer register:
First byte:     I2C Address followed by a low write bit
Second byte: 0b00000000 (points to the conversion register)

2)Send a command to read the conversion register:
First byte:     I2C Address followed by a high read/write bit
Second byte and Third byte: Response with the conversion result

The user has to be able to read the complete coversion result before the next conversion start, therefore the user has to time this process carefully depending on the sampling rate.

At the beginning of your development, it may be easier that you first try to set up the device on "Power down single shot mode" first; this may simplify the timing on your program.

Thanks,

Luis