====== Analog-In/Digital-Out (Potentiometer and LEDs) ======

===== Intro =====

HiTechnic's Prototype Board allows analog input and digital input and output to be easily achieved with a breadboard for circuit prototyping and a LEGO NXT from the Mindstorms robotics kit. This board connects to the standard NXT sensor port and communicates over an I2C serial bus.

The files to accompany the HiTechnic Prototype Board (old version, not "SuperPro") can be found on [[http://www.hitechnic.com/products|HiTechnic'c Downloads page]] or right here:
{{HiTechnic_ExperimentersKitA.zip}}

The PDF handbook included in the file above can also be downloaded here:
{{HiTechnicExperimentersKitHandbookA.pdf}}

===== Wiring =====


  * 220 Ohm Resistor (6)

  * 10k Potentiometer (1)

  * LED (6)

The six LEDs are connected to six pins that will act as a digital out. The potentiometer's variable resistance causes a variable voltage to be read at the analog input AO. This voltage is read in as a number between 0 and 1024. The LEDs are lit up linearly as the potentiometer is rotated.
For example, when the pin A0 reads a voltage corresponding to 200 (~20%), the first LED will light up. At 400, 2 LEDS will light. At 1000 or greater, all LEDs will be lit. This digital-out pin control can be realized in the code excerpt below:

<code c>
...
 if(inputdata>200)  outputdata=b0|b1;
 if(inputdata>400)  outputdata=b0|b1|b2;
 if(inputdata>600)  outputdata=b0|b1|b2|b3;
 if(inputdata>800)  outputdata=b0|b1|b2|b3|b4;
 if(inputdata>1000) outputdata=b0|b1|b2|b3|b4|b5;
...
</code>

{{PotLEDdiagram.jpg}}\\ 
Circuit Diagram from HiTechnic's Experimenter's Kit Handbook\\ 

{{PotCircuitPhoto.jpg}}\\ 
Photo of completed circuit\\ 

===== Video =====

{{youtube>pIjAGGYgIfI?large}}\\ 

**Note:** If the video doesn't work just reload the page.

===== NXC Code =====

<code c PotLED.c>
/*   
Filename: PotLED.nxc
Based on HiTechnic Experimenter's Kit Program

(c) HiTechnic 2009
(c) Alex Alspach 2012

*/


#include "NXCDefs.h"

#define PROTO_PORT IN_1

int inputdata;
int outputdata;
int count;
byte cmndbuf[];                 // buffer for outbound I2C command
byte respbuf[];                 // buffer for inbound I2C response

/* protoboard I/O map
   42,43 - A0 input
   44,45 - A1 input
   46,47 - A2 input
   48,49 - A3 input
   4A,4B - A4 input
   4C    - B inputs
   4D    - B outputs
   4E    - B controls
*/

void readdata()
  {
  ArrayInit(cmndbuf, 0, 2);     // set the buffer to hold 2 values
  cmndbuf[0] = 0x02;            // set write to channel
  cmndbuf[1] = 0x42;            // to set read address
  count=2;                      // 2 bytes to read
  I2CBytes(PROTO_PORT, cmndbuf, count, respbuf);  // issue I2C write command and read the byte back
  inputdata=respbuf[0]*4+respbuf[1];              // create input value by reading the high order byte,
                                                  // shift it left 3 bits and add the low order byt to
                                                  //create a full 10 bit value
  }

void writedata()
  {
  ArrayInit(cmndbuf, 0, 3);     // set the buffer to hold 3 values
  cmndbuf[0] = 0x02;            // set write to channel
  cmndbuf[1] = 0x4D;            // to set write address
  cmndbuf[2] = outputdata;      // to set write data
  count=0;                      // no bytes to read
  I2CBytes(PROTO_PORT, cmndbuf, count, respbuf);  // issue I2C write command and read the byte back
  }

task main()
  {
  
  byte b0 = 1;
  byte b1 = 2;
  byte b2 = 4;
  byte b3 = 8;
  byte b4 = 16;
  byte b5 = 32;
  
  SetSensorLowspeed(PROTO_PORT); // set sensor port 1 to low speed serial (I2C)
  Wait(100);
  
  ArrayInit(cmndbuf, 0, 3);     // set the buffer to hold 3 values
  cmndbuf[0] = 0x02;            // set write to channel
  cmndbuf[1] = 0x4E;            // to set write address
  cmndbuf[2] = 0x3F;            // to write 111111
  count=0;                      // no bytes to read
  I2CBytes(PROTO_PORT, cmndbuf, count, respbuf);  // issue I2C write command
  Wait(100);
  
  while (TRUE)
    {
    readdata();                   // read the analog port 0
    ClearScreen();
    NumOut(20, LCD_LINE1, inputdata);
    outputdata=b0;                      //set the output value to turn one LED on
    if(inputdata>200)  outputdata=b0|b1;     //       based on the input value
    if(inputdata>400)  outputdata=b0|b1|b2;
    if(inputdata>600)  outputdata=b0|b1|b2|b3;
    if(inputdata>800)  outputdata=b0|b1|b2|b3|b4;
    if(inputdata>1000) outputdata=b0|b1|b2|b3|b4|b5;
    writedata();

    Wait(50);
    }
}
</code>

===== Download =====

{{PotLED.zip}}