OPT3101: application questions

Joyce,

 The idea of using a light measuring device is to increase the light levels higher than indoor ambient light, closer to indirect sunlight levels in lux. This is to help with ambient light off set correction using in the calibration method. A Halogen light is recommended because it is the closest man made light to imitating the sun. It has a wider bandwidth and peaks that resemble natural sunlight. 

I don't understand your reference to the x axis unless it is in the GUI Latte. It is based on time or number of samples. 

Joyce,

TMAINC is the actual temperature inside of the OPT3101. it is based on 1degree C resolution and 1degree C accuracy. Because the controller is non floating point there are no digits below the decimal point. TMAIN is a calculated temperature value to get better resolution and is used in all calculations.

The conversion formula for TMAIN from TMAINC:

Temperature (°C) = TMAINC = (TMAIN / 8) – 256

This is covered in the data sheet for more reference. 

Meiling,

  You will have 4 currents for the calibration. You will manually set each current, and use white or black backgrounds. Adjust the distance until you achieve the amplitude code between 16000 and 24000. I try for 20000 for best accuracy. Enter the information for all 4 currents and move to the calibration procedure. When asked place the background at the predetermined distance for the actual clibration. See below. 

In HDR mode you will have 4 currents. In HDR mode, the current can switch between 2 current settings on one TX channel, and with super-HDR, TX1 can be used to add 2 more current settings.

The currents are set in the Configurator tool based on the design of your system. Then output the cpp by selecting the create configuration file in the lower right corner. Replace the existing "OPT3101_configuration.cpp" with the new file.

You need to determine the correct distances for each current. The documentation recommends doing phase offset calibration at a target distance where the amplitude is between 16000-24000. The preset values in the SDK are arbitrary and definitely don’t follow this rule. The values are set like below in OPT3101Coefficients.cpp.

void environmentalController::manuallySetReferenceDistances(){

       this->refDistancesInMM[0][0]=50;

       this->refDistancesInMM[0][1]=120;

       this->refDistancesInMM[1][0]=60;

       this->refDistancesInMM[1][1]=150;

       this->refDistancesInMM[2][0]=0;

       this->refDistancesInMM[2][1]=0;

}

The indexing on refDistancesInMM is [Tx channel] and [current setting, 0 being H and 1 being L]. In order for them to find the proper distances to set for each current and tx setting, you will need to change your configuration to do just one current, flash that, and see at what distance you can get 16000-24000 codes for that particular current. At higher currents, that distance will be pretty far with a white background, so you can use darker backgrounds in order to get lower amplitude settings, but they’ll need to remember what current settings used what color background when you do the calibration.

 Once you know these distances, you can enter that into OPT3101Coefficients.cpp and then use super-HDR configuration and perform the calibration.

Meiling,

  You indicate that you only use TX0. In order to get distances up to 10000mm you will need Super HDR and all 4 currents. This will require calibration of all 4 currents in order to get accuracy to the required distance. Use the System Estimator to understand your optics, mode and distance. It will also define your accuracy if setup correctly.

system estimator tool:  http://www.ti.com/tool/OPT3101ESTIMATOR-SW

Meiling,

  You are correct. HDR uses only TXO with 2 currents. Super HDR uses TXO and TX1 with 4 currents. I do not believe that it is possible to get more than 5 meters with accuracy using only HDR. It will take Super HDR to get 10m -15m distance with accuracy.

I recommend using the system estimator tool:  http://www.ti.com/tool/OPT3101ESTIMATOR-SW so that you will know what kind of accuracy and distances with your optics.

Meiling,

  The first calibration is internal and helps to cancel out electrical and optical crosstalk. By covering the photodiode with black out material, like black tape or using an actual black out tape, it is possible to measure the noise that is left over after the photodiode is cut off. The system corrects for electrical crosstalk and optical cross talk. When the corrections have been completed and applied, read the amplitude level. It should be less than 30 LSB codes. This is a good level to start with because it indicates that you have low noise in the system. If you still have more than 30 LSB codes of amplitude, then you need to look at your system. It may indicate a problem. Read out the amplitude register to see this value. The EVM GUI provides this value to you. 

Meiling,

  I pointed this out a little bit ago. Make sure you pick distances that produce 16000-24000 LSB codes. for each distance. Typically this is where you will see this kind of error. Remember you can change the reflectivity of the back ground, either white or black to get the correct amplitude while determining the distances. See below. 

  You will have 4 currents for the calibration. You will manually set each current, and use white or black backgrounds. Adjust the distance until you achieve the amplitude code between 16000 and 24000. I try for 20000 for best accuracy. Enter the information for all 4 currents and move to the calibration procedure. When asked place the background at the predetermined distance for the actual clibration. See below. 

In HDR mode you will have 4 currents. In HDR mode, the current can switch between 2 current settings on one TX channel, and with super-HDR, TX1 can be used to add 2 more current settings.

The currents are set in the Configurator tool based on the design of your system. Then output the cpp by selecting the create configuration file in the lower right corner. Replace the existing "OPT3101_configuration.cpp" with the new file.

You need to determine the correct distances for each current. The documentation recommends doing phase offset calibration at a target distance where the amplitude is between 16000-24000. The preset values in the SDK are arbitrary and definitely don’t follow this rule. The values are set like below in OPT3101Coefficients.cpp.

void environmentalController::manuallySetReferenceDistances(){

       this->refDistancesInMM[0][0]=50;

       this->refDistancesInMM[0][1]=120;

       this->refDistancesInMM[1][0]=60;

       this->refDistancesInMM[1][1]=150;

       this->refDistancesInMM[2][0]=0;

       this->refDistancesInMM[2][1]=0;

}