The TCS230 color sensor module

The TCS230 color detector measures three primary colors Red, Green and Blue and also has a separate white light detector. Since any color can be created from different levels of these primary colors, you can find out the color composition of a light source.

The four LEDs on the breakout board (shown below) are there to illuminate the subject with an even light source, making measurement more reliable.

You can use the TCS230 (or newer device TCS3200 see here for differences) where you need to take action based on the color of an object. The device reacts to infrared so may need an infrared filter or use the device in an enclosed space.

The TSC230 chip mounted on a breakout board.

TCS230 Specification

TCS230 Datasheet

Download the datasheet here.

How the TCS230 works

The output from TC230 is from a single square wave output that changes frequency with the amount of light sensed. The specific sensor R,G,B or W is selected using two digital control inputs (S0 and S1).

The frequency of the square wave is proportional to the amount of light falling on a set of light detecting diodes. Since there are four different sources of information red, green, blue and clear photodiodes - each of these is selected in-turn using (S0 and S1). So only one set of photodiodes is connected at a time to generate the output.

The chip inputs, S2 and S3, control the output frequency divider logic which you an use to get a different output frequency proportional to the colour level. You can select a longer output pulse to accommodate slow processor measurement capability - but the reading averages to the same output value regardless of frequency output.

In the photo below you can see the individual red, blue, green and clear filters. It's a bit blurry - but that was a very difficult photo to get and remember each section is 120um square so each one is about the width of a hair (17-181um) [Brian ley]!

Close up of the TCS230

Zoomed in filters of the TCS230 from image above.

In fact several photodiodes for each color are connected in parallel and these are spread evenly over the sensor surface - you can see this in the photo above. This layout obtains an overall reading for each color not just from an individual photodiode. For the TCS230 there are a total of 64 photodiodes. 16 have a red filter above them, 16 have a green filter, 16 have a blue filter and 16 have a clear filter.

Block Diagram showing how the Chip works

Signal output

The signal output by the TCS230 is obtained by a current to frequency converter that takes as its input the average current from the selected set of photodiodes. The idea is that you switch one set on, take a reading and then switch to the next set until all four measurements are done. The output signal is a square wave with even mark to space ratio: 50% high, 50% low.

Frequency Dividers

The square wave output by the device can also be divided down (internally in the TCS230) and this allows slower processors to to make measurements more easily. There is no measurement penalty as the divided down output is simply an average of the original. The only disadvantage is that because the signal is of a lower frequency you can not make measurements as quickly.

If it was important to make a light reading very fast then you would want to use a high speed processor and not divide down the output signal. You can imagine that this might become important in an industrial process measurement e.g. for measuring the state of a product e.g. you would want to quickly measure the color of an item on a conveyor belt, and reject it if it as the wrong color.

Frequency outputs

The maximum full scale frequency output from the TCS230 are shown below for the scaling factors controlled by S0 and S1. Scaling is really just using an internal clock chip that counts the input signal (the primary clock output from the photodiode current to frequency converter) and generates divided down clocks.

Note: For the TCS230, TCS3200 and TCS3210 the above parameters are identical.

How to use the TCS230

On an Arduino the easiest way to use the TCS230 is to use the pulseIn() function, first setting the dividers to output the lowest frequency.

Difference between TC230 and TCS3200

Specification of the TCS230 where different to TCS3200 and TCS3210

Note: Typical values are shown above.

From the above table you can see that the TCS3200 and TCS3210 have been optimized for low power operation (in power down mode) and also for operation below 0°C.

If you want really low power when the chip is in shut down mode, then the TCS3200/3210 have a guaranteed maximum of 0.1uA, whereas the TCS230 can go up to 15uA. The TCS3200/3210 can also operate up to -40°C, whereas the TCS230 can't operate below 0°C.

TCS230 Circuit Layout

Figure 1 : Fritzing Layout for the TCS230 or TCS3200 breakout board

Schematic

The following schematic shows connections from a TCS230 breakout board to an Arduino Uno, with output on pin 4 and the two photodiode selector muxes on S0 and S1 (attached to pins 10 & 11).

The output frequency divider controls are  on S2 and S3 ( attached to pins 1 & 2). The output enable is on pin 7, and the digital output from the TCS230 is connected to the Uno as an input on pin 4.

Software Library and versions

Arduino IDE Version

Version : 1.8.3

Library

None used: Just use the function pulseIn.

Example Sketch for Arduino UNO

Hitting any key will both show you the current sensor readings (RGB) and try to detect the current color. Current colors are stored in two arrays:

• int RGB[[NUMCOL][3]
• char colname[NUMCOL][11]

The RGB array holds the color values to be found while the colname array holds the text you want to display for the corresponding RBG value.

TCS230 Calibration

The sensor is very sensitive to any changes in light and in practice that means any slight distance changes from the sensor to the object will cause a different reading. Additionally any ambient light changes will also cause a different reading.

So to make accurate (repeatable) readings you need to control two elements:

• Ambient light.
• Distance to object.

To calibrate the sensor, push the sensor down onto colored paper as even a small adjustment fails since the sensor is extremely sensitive.

Set the serial monitor to 115200 Baud and push the sensor down and hit the 'Enter' key in the serial monitor input field. This will then show you the current RGB values. Copy these values into the RBG array and set the equivalent colname text. Recompile (or add some different colored objects). Recompile and check that the 'color' is found.

Now you can test the 'objects' with the code now reporting the color of the object.

As for "real" calibration- Its difficult and the only way you will achieve it is to place the sensor in a closed environment where you can control the lighting levels - this will give repeatable reliable measurements.

Click in the code below to copy it to the clipboard.

//
// Detect colors using TCS230.
//

// Arduino uno pins for control of TCS230
#define TCS320_OE 7
#define TCS320_S0 10
#define TCS320_S1 11
#define TCS320_S2 2
#define TCS320_S3 3
#define TCS320_OUT 4

#define variance 50  // Acceptable detection error 2%.

#define SEL_RED  \
   digitalWrite(TCS320_S2,LOW);digitalWrite(TCS320_S3,LOW)
#define SEL_GREEN \
   digitalWrite(TCS320_S2,HIGH);digitalWrite(TCS320_S3,HIGH)
#define SEL_BLUE \
   digitalWrite(TCS320_S2,LOW);digitalWrite(TCS320_S3,HIGH)
#define SEL_CLEAR \
   digitalWrite(TCS320_S2,HIGH);digitalWrite(TCS320_S3,LOW)

#define TWO_PER \
   digitalWrite(TCS320_S0,LOW);digitalWrite(TCS320_S1,HIGH);

#define debug(a) Serial.println((a));


#define NUMCOL 5

// int RGB[NUMCOL][3]; // Five colors with 3 elements.
// Array of NUMCOL strings len 10. 11 for null.
// char colname[NUMCOL][11];

// Typical values for 2% dividers (set variance to 50).
int RGB[NUMCOL][3]={
   {248,647,393},
   {188,261,265},
   {404,710,546},
   {506,493,304},
   {930,1199,837},
};

char colname[NUMCOL][11]={
"red",
"yellow",
"brown",
"blue",
"black",
};

////////////////////////////////////////////////////////////////
void setup() {

   pinMode(TCS320_OE,OUTPUT);
   pinMode(TCS320_S0,OUTPUT);
   pinMode(TCS320_S1,OUTPUT);
   pinMode(TCS320_S2,OUTPUT);
   pinMode(TCS320_S3,OUTPUT);
   pinMode(TCS320_OUT,INPUT);

   TWO_PER;

   digitalWrite(TCS320_OE,LOW); // On always.

   Serial.begin(115200);
   Serial.println("TCS230 color detector");
}

////////////////////////////////////////////////////////////////
unsigned long get_TCS230_reading(void) {
  unsigned long val;
  noInterrupts();
  val = pulseIn(TCS320_OUT,HIGH,20000); // 2000us=2ms  2Hz min.
  interrupts();
  return val;
}

static int clr,red,green,blue;

////////////////////////////////////////////////////////////////
uint16_t detect(void) {
   unsigned long val;

    SEL_RED;
    red = val = get_TCS230_reading();
    Serial.print("RED: "); Serial.print(val);

    SEL_GREEN;
    green = val = get_TCS230_reading();
    Serial.print(" GREEN: "); Serial.print(val);

    SEL_BLUE;
    blue = val = get_TCS230_reading();
    Serial.print(" BLUE: "); Serial.print(val);

    Serial.print(" \n");
}

////////////////////////////////////////////////////////////////
int withinEQ(int c, int xl, int xh) {
   if (c>=xl && c<=xh) return 1;
   return 0;
}

////////////////////////////////////////////////////////////////
// Compare a value to a value and variance.
int compare(int c, int v, int err) {
int xh=v+err, xl=v-err;
   if (withinEQ(c,xl,xh)) return 1;
   return 0;
}

////////////////////////////////////////////////////////////////
void loop() {
uint8_t chr,i,fnd;

   if (Serial.available()>0) {

      chr = Serial.read(); // Consume.

      // Find color match.
      detect();
      fnd=0;
      for (i=0;i<NUMCOL;i++) {
         if ( compare(red,RGB[i][0],variance) &&
              compare(green,RGB[i][1],variance) &&
              compare(blue,RGB[i][2],variance)
            ) { // Found
              Serial.print("Col is :");
              Serial.println(colname[i]);
              fnd=1;
              break;
            }
      }
      if (!fnd) Serial.println("NOT Found");
   }
}

Why does the code use 2 percent dividers?

You can choose to use raw 100%, 20% or 2% output and most other code examples use 20%.

The function used to measure the output of the chip is pulseIn, which is accurate to 4us, so to get maximum accuracy we need an output that is big enough compared to the accuracy of pulseIn.

The following data is taken from my setup which is probably an average lighting setup in an office. These are provided to show the typical minimum and maximum periods in microseconds that are available for measurement using the pulseIn function.

The questions to be answered are:

What effect does changing the divider output from the TCS230 have on the output periods to be measured?

How does changing the dividers affect the output periods?

Typical output for 2 percent dividers:

{248,647,393},

{188,261,265},

{404,710,546},

{506,493,304},

{930,1199,837}

The maximum and minimum periods from the above measurements are:

1199us and 188us

Here the frequencies involved are :

1.0/1199e-6 = 834Hz to 1.0/188e-6 = 5319Hz (5.3kHz). (max is 12kHz - T=83us).

Typical values for 20 percent dividers:

{18,26,26},

{48,47,30},

{40,69,54},

{27,71,43},

{92,119,83}

The maximum and minimum periods from the above measurements are:

119us and 18us.

Here the frequencies involved are :

1.0/119e-6 = 8403Hz to 1.0/18e-6 = 55555Hz (55kHz). (max is 120kHz - T=8.3us).

Typical values for raw output

The quoted max frequency is 600kHz - not measured. The period will be 1.6us.

Conclusion

For the 20% dividers you are getting close to the measurement capability of pulseIn which is 4us i.e the minimum period measured was 18us and that is only -5 counts of pulseIn data. So that measurement is getting close to being too small and therefore less accurate i.e. the difference between colors will need to be larger to register a difference in the chip output = less sensitive.

The resolution here is 22% of the minimum period which is fairly bad.

The periods for 100% output will be even smaller (1.0/600e3 = 1.6us) and that would not be measurable using pulseIn - you may be able to do it using the asynchronous input in Timer 2.

When the 2% dividers are used the program can make the most accurate period measurement since the periods output by the chip are long compared to the pulseIn accuracy of 4us. i.e the lowest period measured was 188us for these dividers ( ~48 periods of 4us ) compared to 18us ( ~5 periods of 4us ) for the 20% dividers.

The resolution here is 2.13% of the minimum period which is quite good.

Therefore the 2% divider output is the better option for measurement accuracy.

Details on Color Detection

The spectral response of the photodiodes is interesting in that all the photodiodes react to infrared light (periods above 700nm). When you add in the green and blue filters, each response shows two peaks one in the visible spectrum and one in the infrared spectrum. So when you use the TCS230 or TCS3200 (same photodiodes) for measuring red, green, blue or white light you will be actually gathering an infrared response as well. So this is definitely not the same response as your eye's response to light.

The question is: Does that really matter? ...and the answer is: It depends!

If your project is trying to measure a response that is as close as possible to a human eye response then yes it does matter. If on the other hand, the project is sorting items based on color, and is used in a well defined environment, (not changing between florescent and incandescent bulbs) then no, it does not matter.

As long as the detector is enclosed in a defined environment then it will always operate the same way i.e. within a machine closed in, with its own LED light source; The output of the detector will generate the same measurement results (however, consider aeging and temperature effects).

In the data sheet for the TCS230 there are two spectral diagrams: copied below . In addition I have added the color spectrum chart from wikipedia that shows a human eye response.

It is important to note that the color detection of the photodiodes themselves is affected by infrared and to get a better result that is not affected by infrared you have to use an infrared filter.

This is the response of the TCS230 with no infrared filter on the left and with an infrared filter on the right.

[Source: the TAOS datasheet].

On the left you can see that the Green response has two peaks (~550nm and ~830nm) , the Blue response has two peaks (~470nm and ~800nm) and the Red response goes from 600nm to 1100nm. The maximum response you really want is from 450nm to 700nm, since the 700nm wavelength is the maximum your eye can detect. This means any infrared radiation that your eye can not see will affect Red, Green and Blue readings unless an IR filter is used.

Filters suggested by TAOS are:

• Schott BG18
• Schott BG39
• Hoya CM500

When you use an IR filter(right hand diagram above) the filter smoothly chops out wavelengths above 700nm and there is only one peak response per type of photodiode. The response is far more similar to the human eye response shown below.

[source https://en.wikipedia.org/wiki/Color]

The only trouble with those Hoya or Schott filters is tha they cost a lot more than the sensor itself; You can find a cheap IR filter on ebay by searching for X2 ir-cut CS lens mount.

Conclusions

TCS230 Color Detection

The best way to get a more accurate color detection, that more closely matches the human eye response, is to use an infrared filter in front of the the sensor. Note that this also applies to the TSC3200 and TCS3210 as these also employ similar photodiodes that have similar response curves.

However you can still use the devices without an IR filter and will still get color results as long as the lighting conditions and distance from the object are kept constant.

Divider control (S3, S4)

Most code uses 20% divider operation - this gives out pulses that are too small for pulseIn - on an Arduino Uno - (it just about manages to measure them). It is therefore better to use 2% dividers resulting in longer output pulses that pulseIn can easily measure.

Written by John Main who has a degree in Electronic Engineering.

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