Showing posts with label level-shift. Show all posts
Showing posts with label level-shift. Show all posts

1/03/2013

Electronic compass part 2

This is part 2 of the electronic compass with the video and the Arduino sketch.

Video:



Sketch:

/*****************************************
 * Compass with Pollin HDMM01-compass-module
 * and Nokia 5110-display
 * Last edit: 3.1.2013
 * By Markus Ulsass
 ******************************************/

/*******************************************************************************
 * This is an example sketch for our Monochrome Nokia 5110 LCD Displays
 *
 * Pick one up today in the adafruit shop!
 * ------> http://www.adafruit.com/products/338
 *
 * These displays use SPI to communicate, 4 or 5 pins are required to
 * interface
 *
 * Adafruit invests time and resources providing this open source code,
 * please support Adafruit and open-source hardware by purchasing
 * products from Adafruit!
 *
 * Written by Limor Fried/Ladyada  for Adafruit Industries.
 * BSD license, check license.txt for more information
 * All text above, and the splash screen must be included in any redistribution
 *******************************************************************************/

#include <Adafruit_GFX.h>
#include <Adafruit_PCD8544.h>

#include <Wire.h>

#define  I2ADDR       0x30
#define  TakeMeasure  0x01
#define SET_COIL 0x02 // set magnetic coil
#define RESET_COIL 0x04 // reset magnetic coil

// pin 7 - Serial clock out (SCLK)
// pin 6 - Serial data out (DIN)
// pin 5 - Data/Command select (D/C)
// pin 4 - LCD chip select (CS)
// pin 3 - LCD reset (RST)
Adafruit_PCD8544 display = Adafruit_PCD8544(7, 6, 5, 4, 3);

int r = 24;  // radius of compass rose
int x0= 60;  // x-origin
int y0 = 24; // y-origin

void setup()   {

  // Serial.begin(9600);

  display.begin();
  display.setContrast(60);
  display.clearDisplay();

  Wire.begin();

}

void loop() {

  ResetSetCoils();
 
  byte MsbX,LsbX,MsbY,LsbY;
  int x,y;
  char line[80];
  Wire.beginTransmission(I2ADDR); // Pollin HDMM01 address
  Wire.write(0x00);  
  Wire.write(TakeMeasure);
  Wire.endTransmission();
  delay(20);
  Wire.beginTransmission(I2ADDR);
  Wire.write(0x01);
  Wire.requestFrom(I2ADDR, 4);

  while(Wire.available()<4);
  MsbX  =Wire.read();          // upper  4 Bit X
  LsbX  =Wire.read();          // lower 8 Bit X
  MsbY  =Wire.read();          // upper 4 Bit Y
  LsbY  =Wire.read();          // lower 8 Bit Y
  Wire.endTransmission();         // stop transmitting
  x=((MsbX&0x0f)*256)+(LsbX);
  y=((MsbY&0x0f)*256)+(LsbY);
  x = map(x, 1960, 2151, -180, 180);
  y = map(y, 1939, 2131, -180, 180);
  double mygrad = atan2(-x, y)*180/3.1415927410;
  if (mygrad < 0)    mygrad = mygrad +360;
  int angleActual = mygrad;
  // Serial.println(mygrad); // debug
  delay(200);

  // Calculation of compass needle on lcd pointing to the direction
 
  if (angleActual >= 0 && angleActual <=45) {
    // 0-45 degrees
    int angle = angleActual/2;
    display.drawLine(x0, y0, x0+angle, y0-r, BLACK);
    // 45 degrees
    // display.drawLine(x0, y0, x0+r, y0-r, BLACK);
  }
  else if (angleActual >45 && angleActual <=90) {
    // 46-90 degrees
    int angle = (angleActual-44)/2 ;
    display.drawLine(x0, y0, x0+r, (y0-r)+angle, BLACK);
    // 90 degrees
    // display.drawLine(x0, y0, x0+r, y0, BLACK);
  }
  else if (angleActual >90 && angleActual <=135) {
    // 91-135 degrees
    int angle = (angleActual-90)/2;
    display.drawLine(x0, y0, x0+r, y0+angle, BLACK);
    // 135 degrees
    // display.drawLine(x0, y0, x0+r, y0+r, BLACK);
  }
  else if (angleActual >135 && angleActual <=180) {
    // 136-180 degrees
    int angle = (angleActual-134)/2;
    display.drawLine(x0, y0, (x0+r)-angle, y0+r, BLACK);
    // 180 degrees
    // display.drawLine(x0, y0, x0, y0+r, BLACK);
  }
  else if (angleActual >180 && angleActual <=225) {
    // 181-225 degrees
    int angle = (angleActual-178)/2;
    display.drawLine(x0, y0, x0-angle, y0+r, BLACK);
    // 225 degrees
    // display.drawLine(x0, y0, x0-r, y0+r, BLACK);
  }
  else if (angleActual >225 && angleActual <=270) {
    // 226-270 degrees
    int angle = (angleActual-222)/2;
    display.drawLine(x0, y0, x0-r, (y0+r)-angle, BLACK);
    // 270 degrees
    // display.drawLine(x0, y0, x0-r, y0, BLACK);
  }
  else if (angleActual >270 && angleActual <=315) {
    // 271-315 degrees
    int angle = (angleActual-270)/2;
    display.drawLine(x0, y0, x0-r, y0-angle, BLACK);
    // 315 degrees
    // display.drawLine(x0, y0, x0-r, y0-r, BLACK);
  }
  else if (angleActual >315 && angleActual <=360) {
    // 316-360 degrees
    int angle = (angleActual-312)/2;
    display.drawLine(x0, y0, (x0-r)+angle, y0-r, BLACK);
    // 360/ 0 degrees
    // display.drawLine(x0, y0, x0, y0-r, BLACK);
  }

  // text display

  // display.drawCircle(x0, y0, r-1, BLACK);
  // Display actual heading
  display.setTextSize(2);
  display.setTextColor(BLACK);
  display.setCursor(0,0);
  display.println(angleActual);
 
  display.setTextSize(1);
  display.setTextColor(BLACK);
  display.setCursor(x0-2,0);
  display.println("N");
 
  display.setTextSize(1);
  display.setTextColor(BLACK);
  display.setCursor((x0+r)-5,y0-3);
  display.println("0");
 
  display.setTextSize(1);
  display.setTextColor(BLACK);
  display.setCursor(x0-2,y0+r-8);
  display.println("S");
 
  display.setTextSize(1);
  display.setTextColor(BLACK);
  display.setCursor((x0-r)+5,y0-3);
  display.println("W");
 
  // Triangle for direction
 
  // display.drawTriangle(int16_t x0, int16_t y0, int16_t x1, int16_t y1, int16_t x2, int16_t y2, uint16_t color)
  display.drawTriangle(0, 46, 20, 46, 10, 18, BLACK);
  // fillTriangle ( int16_t x0, int16_t y0, int16_t x1, int16_t y1, int16_t x2, int16_t y2, uint16_t color)
  display.fillTriangle (0, 46, 20, 46, 10, 18, BLACK);
  display.display();
  delay(100);
  display.clearDisplay();

}

void ResetSetCoils (void)
{

    // RESET / SET Coils
    Wire.beginTransmission(I2ADDR);
    Wire.write(0x00);
    Wire.write(RESET_COIL);
    Wire.endTransmission();
    delay(1);
    Wire.beginTransmission(I2ADDR);
    Wire.write(0x00);
    Wire.write(SET_COIL);
    Wire.endTransmission();
    delay(1);
}

12/23/2012

Level-Shifter for XBee & Raspberry Pi

Some projects have mixed supply voltages (e.g. 5 Volt and 3.3 Volt) and sometimes integrated circuits don't work with those unequal signal levels - or worse get damaged by the higher level supply signals.
Level shifter pcb

In case of the XBee which is driven by 3.3 Volt up to now I added a simple resistor divider to get the signals down to the lower supply level (see this older post ). But even if you feed the XBee without translating the different supply levels, I never got any problems (but I wouldn't recommend).

It might look slightly different with the Raspberry Pi, so to be on the safe side I built a simple 2-bit bidirectional voltage-level translator circuit for the alleged thin-skinned RasPi. You just need four 10k resistors, two BSS138 (N-Channel Logic Level Enhancement Mode Field Effect Transistor) and two four-pin headers.

I etched the board by myself but if you want to take the short way, there are already breakout boards and ICs available (e.g. Sparkfun Logic Level Converter, TXS0102 from Texas Instruments or ADuM1250/ ADuM1251 from Analog Devices).

Anyway I wanted to do some practice with my favourite pcb layout software Eagle and designed this simple pcb.

How does the level shifting work? If nothing happens on the bus (in this special case on the I2C-bus, thats what the pcb is labled for, but it also works with RX/ TX or any other 2-bit bidirectional digital purposes) all signals are pulled high by the 10k resistors. If either side goes low, the N-Channel MOSFET steps in and also pulls the signal line low, either because it turns on (low level side) or passes through the body diode (high level side).