I2C and SPI

I2C (Inter Integrated Circuit Communications, pronounced I squared C) and SPI (or Serial-Peripheral interface) are protocols that can link a microcomputer to other micros or integrated circuits.
Both protocols are widely used in hobby electronics and robotics projects.
I2C was originally developed by Philips (now nxp) and is used in all sorts of equipment including virtually every tv, monitor and computer motherboard. I2C is a flexible protocol but has fairly limited bandwidth.
SPI was originally developed by Motorola (now Freescale). It’s simple and fast but has some limitations compared to I2C.
Most modern micro-controllers have hardware support for both protocols. Examples include the Arduino, mbed, BeagleBone, BeagleBoard and Raspberry Pi.
Let’s look at the two protocols in a little more detail.

I2C

I2C can be used to connect up to 127 nodes via a bus that only requires two data wires, known as SDA and SCL.
Since the devices need a common voltage reference (Ground) and a power line (referred to as Vcc or Vdd) the full bus has four wires, two for data and two for power. Sometimes additional lines are added, for example to support interrupts when the state of I2C devices change.

In theory the I2C bus can support multiple masters, but most micro-controllers can’t. A master is usually a microcontroller, although it doesn’t have to be. Slaves can be ICs or microcontrollers.

In the diagram above a RasPi is a master and there are several slaves: a Digital-to-Analog converter (DAC), an Analog-to-Digital converter (DC), and an Arduino.

I2C can be used to control a very wide range of devices. Common examples include

• Digital-to-analogue converters (DACs)
• Analogue-to-digital converters (ADCs)
• LCD displays
• OLED Screens
• Keyboards
• Motor drivers
• LED drivers
• Memory chips and cards (EEPROM, RAM, FERAM, Flash)
• bus expanders/extenders (chips with 8 or 16 I/O pins controllable via I2C)
• other microcontrollers

When the master wishes to communicate with a slave it sends a series of pulses down the SDA and SCL lines. The data that is sent includes an address that identifies the slave with which the master needs to interact. Addresses take 7 bits out of a data byte; the remaining bit specifies whether the master wishes to read (get data from a slave) or write (send data to a slave).

Some devices have an address that is entirely fixed by the manufacturer; others can be configured to take one of a range of possible addresses. When a micro-controller is used as a slave it is normally possible to configure its address by software, and for that address to take on any of the 127 possible values.

The address byte may be followed by one or more byes of data, which may go from master to slave or from slave to master.

When data is being sent on the SDA line, clock pulses are sent on the SCL line to keep master and slave synchronised. Since the data is sent one bit at a time, the data transfer rate is one eighth of the clock rate. The original standard specified a standard clock rate of 100KHz, and most I2C chips and micro-controllers can support this. Later updates to the standard introduced a fast speed of 400KHz and a high speed of 1.7 or 3.4 MHz. The Arduino can support standard and fast speeds; the BeagleBoard has three I2C busses, one at each speed; the RasPi and BeagleBone can both support standard and fast I2C.

The fast rate corresponds to a data transfer rate of 50K bytes/sec which is too slow for some control applications. One option in that case is to use SPI instead of I2C.
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Arduino: I2C Communication between 2 Arduinos with Wire Library

The next method of communication I will look at is I2C communication. I2C stands for Inter-integrated circuit. It allows one master device to connect to a large number of slave devices using only 2 pins (signal and clock).  The nice folks at Arduino have made this very easy with the Wire library. It is included with the Arduino IDE and is supported on most Arduino boards.

Before we begin you may want to peruse the Arduino website. The Wire library is described HERE and detailed HERE.  When you finish those, let's dive in.

The first thing I did was run the master_reader and slave_sender examples. This was very easy. It sends hello from the slave to the master and displays it on the serial monitor.

Below is a picture of the wiring. It is simple. Wire the SCL pins and the SDA pins together through a pull-up resistor. I used 4k7. A good example can be found at THIS instructable. You also need to connect the grounds of the two boards as well as the vcc. I copied over the diagram for convenience (to the right).

Next I decided to make it transmit something useful. I made an I2C HC-SR04. The slave Arduino constantly takes distance measurements with the HC-SR04 sonar module. The master Arduino can then poll the slave whenever it wants to get the current distance measurement.

Wiring is the same as above. Make sure you use your pull-up resistors. I connected the trigger pin of the sonar to pin 7 and the echo to pin 8, but you could use any of them.

HERE is my code. Hopefully I will have time to rewrite the slave for the ATtiny in the future. That is the plan. Right after wireless communication, robot arm, computer vision..

Matthew

SPI

The SPI interface was originally developed by Motorola (now Freescale). SPI is much simpler than I2C. Master and slave are linked by three data wires, usually called MISO, (Master in, Slave out), MOSI (Master out, Slave in) and M-CLK.

As the names suggest, the M_CLK line carries clock pulses which provide synchronisation. When a transfer is taking place, a bit of data is transferred via MOSI from Master to slave and at the same time a bit of data is transferred via MISO from Slave to Master. At the end of eight clock pulses an entire byte of data has been transferred in each direction.

Many SPI-enabled ICs and Microcontrollers can cope with data rates of over 10MHz, so transfer is much faster than with I2C. The downside is that SPI normally has no addressing capability; instead, devices are selected by means of a Chip Select signal which the master can use to enable one slave out of several connected to the SPI bus. If more than one slave exists, one chip select line is required per device, which can use precious GPIO lines on the Master.

SPI is less well specified than I2C, but the SPI module on the Broadcom chip at the heart of the Raspberry Pi is flexible enough to cope with most common SPI devices.

Digital Oscilloscope based on Arduion

We often see someone making a digital oscilloscope on the net. The digital oscilloscope generally has a module of A/D transtion, and there are two kinds of circuit according to the method of A/D transtion: 1. Special ADC chip with mircocontroller, 2.making use of the interal ADC function.
 As to the first method, I have made two, but the circuit is a little difficult and the components is not easy to get on hand, which is difficult for the electronic beginner.
The second method is comparatively simply, but has a obvious  weakness,  i.e. the bandwidth is narrow. A typical work made by a American guy, (see http://www.serasidis.gr/circuits/AVR_oscilloscope/avr_oscilloscope.htm), has a 7.7KHz bandwidth. And some people made it with AVR and STC, but also their bandwidth does not exceed 10KHz.

  Recently I have seen a guy using Arduino to build digital oscilloscope, which is even more simple than the second method. But still doesn't work well with narrow bandwidth. Therefore I want to have a try to see if there is better way to solve this problem. After making and testing, and modifying codes constantly, I can now improve the sampling frequency and make a big progress.
  The specification of the final work is as follow:
  response frequency: 10-50 KHz,
  Power Supply: 5V
  LCD: 128*64
  Measuring Display Zone: 96X64
  Message Display Zone: 32X64, indicates the frequency and Vpp,etc.
  SYNC Method:   Rising along the trigger
  Scan Speed: 0.02ms/div 10ms/ div, 9 grades according to 1-2-5
  Hold Function:  hold displaying wave and parameters

STEP 1 PROTOTYPE TESTING

 The best advantage for arduino is its abundant resources, and you need not to know much thing about microcontroller. I make use of the library of LCD: u8glib.h, which makes programming very easy, otherwise to drive LCD will waste you a lot of time.

  Below is my test circuit with Arduino UNO, and 12864 LCD controlled by ST7920.

Now input all this codes and compile them, the oscilloscope starts working. Isn't is easy?

#include <U8glib.h> //声明库
 U8GLIB_ST7920_128X64_4X u8g(13, 12, 11); // 声明液晶屏 SPI Com: SCK =13, MOSI = 12, CS =  11
 int x,y; //绘点坐标
 int Buffer[128]; //缓存值储存数组
 void setup( ) {  } 
 //采样
 void sample( )  
{  
 for(x = 0;x < 128;x++) 
   Buffer[x] = analogRead(A0);  //信号采样
 for(x = 0;x < 128;x++)  
   Buffer[x] = 63-(Buffer[x]>>4); //计算纵坐标值
}
//显示
void draw( )  
{  
  for(x = 0;x < 127;x++)  
     u8g.drawLine(x,Buffer[x],x,Buffer[x+1]);  //画相邻两点连线  
 u8g.drawLine(64,0,64,63); // 画坐标轴 
 u8g.drawLine(0,32,128,32);
 for(x=0;x<128;x+=8)   //画坐标轴刻度 
   u8g.drawLine(x,31,x,33);
 for(x=0;x<64;x+=8)
   u8g.drawLine(63,x,65,x);
 u8g.drawFrame(0,0,128,64); //画边框 
}   
void loop( ) 
 { 
   sample();         //采样
   u8g.firstPage();  //清屏
   do  draw( );      //显示
   while( u8g.nextPage( ));
 } 

With this prototype circuit, I measured one ADT time for Arduino is about 111ms using analogyread() function, which is very slow, meaning the bandwith is only 1KHz. So the next step is to raise the AD transition speed.

STEP 2  Building Complete Machine

  When I performed the experiment , I use Arduino UNO, Now I replace it with Arduino Pro mini so that I can make the volume small.

   Circuit:

Components list:

 Arduino PRO mini

 LCD 12864

 Capacitor: 100μF  25V

 Potentiometer: 50K

 Peg Board

 Button Switch

 Power Switch

 Battery holder

 Main Case

1. Solder Arduino PRO mini

2. Solder Peg board

3. Make LCD Peg board

4.Assemble circuit board

5. Make main case

6.Total assembly

STEP 3  downloading codes and testing

Building a Digital Oscilloscope from a DIY Kit

written by Josehf Murchison

I have a number of oscilloscopes; the only one I didn’t build or rebuild is my DSO Nano oscilloscope. The vacuum tube oscilloscopes were weeklong projects unlike the DSO 062 oscilloscope that took only two hours to assemble. This is my second DSO 062 LCD Oscilloscope my other one managed to grow legs and go on a trip without me. I purchased the kit from China www.aliexpress.com for $40, it is very cheap in China as tremendous electronic gadgets are manufactured there.

Since the Assembly Notes have step by step instructions on how to assemble the scope most of this Instructable will be on the things not in the Assembly Notes. And little tricks I learned through the years working in electronics

Step 1: The Kit

When your DSO 062 Oscilloscope arrives in the mail open it, inside you will find several packages of parts and two pieces of paper marked, “General Assembly Guide and 062 Oscilloscope Quick Reference”. Put everything back in the box but the paper marked “062 Oscilloscope Quick Reference”.

Take the quick reference to your computer, on the bottom of the quick reference it says “For Complete and updated documents please visit: http://www.jyetech.com that is JYETECH.

On your computer go to:
http://www.jyetech.com

Click on English

Under Quick Links Click on Documents

Down load all the files under models 06203P, 06203KP, and 06204KP for all three models it is the same files.

Quick Reference
Operating Instructions
Assembly Notes
Troubleshooting Guide
Assembly Back
Assembly Front
How to Upgrade Firmware by Bootloader
How to Program 062 Oscilloscopes
Part list
Schematic

Step 2: Print Files

Print the pdf files:

Assembly Notes
Troubleshooting Guide
Assembly Front
Assembly Back
Part list
Operating Instructions

The reason for printing the pdf files is so you can tick off the steppes as you follow the assembly notes.

Step 3: Check the Parts

From the printed pdf files check the parts make sure all the parts are in the kit and check them to be sure they fit the circuit board. Whether deliberately or by accident it is not uncommon for parts to be substituted in kits, so make sure they are the right parts and they fit before you start to assemble your oscilloscope.

Step 4: Tools

If all the parts are in the kit and they fit in place you will need these tools to assemble the oscilloscope. Power supply 9 to 12 volts DC 300 ma Multimeter Soldering iron Side cutters Wire striper Needle nose pliers Phillips screwdriver Solder

Step 5: Assembling the Oscilloscope 

Take your time and follow the step by step instructions of the assembly notes, the only thing I would add to them is use the long spacers to hold the circuit board up from your work table. Cut off the excess leads off the through hole parts as you add them to the circuit board or it will be like trying to solder through a hair brush. Your joint is good on the through hole parts if you can pluck the end of the excess wire lead and it rings like a guitar string.

Step 6: Testing 

 After assembling the circuit board completely you need to test the oscilloscope before putting the front and back plates on. Connect the power to the oscilloscope. The LCD should light up. “Boot loader” then should come on the LCD. The LCD should switch to WWW.JYETECH.COM. Last F= and Hz This indicates the oscilloscope is functioning normally, if it doesn’t display this on the LCD follow the Troubleshooting Guide.

Step 7: Assembling the Probe 

Strangely the assembly notes don’t tell you how to put the probe together, so in this step I will. After the oscilloscope is completely assembled gather the parts for the probe. Strip ¼ inch of the insolation off both ends of the small red and black wires and solder one end onto the alligator clips. Slip the rubber boots on to the alligator clips and slip the small shrink tube on to the wires. Next strip ½ inch of the insolation off the outside layer of the coaxial cable. Twist the outer braded wire. Strip ¼ inch of the insolation off the inner wire. Solder the red wire to the inner wire and the black wire to the outer braded wire. Slip the shrink tube over the joints and heat to shrink then slip the larger shrink tube over the two joints and heat to shrink.

Step 8: The BNC Connector 

Slip the BNC connectors collar over the coaxial cable and strip the end as before. Solder the center wire to the center tab of the BNC connector and the outer braded to the outer tab of the BNC connector. Then screw the collar back on the connector.

Step 9: Testing the Probe and Oscilloscope

To test the probe and oscilloscope I connected the probe to the built in signal generator of my DSO Nano oscilloscope. Now when I power up the oscilloscope it said F= 1000Hz after booting up. Then I checked the other functions of the oscilloscope.

Step 10: Making a Portable Power Supply

 All the parts for this I got at my local Radio Shack the Source here in Canada. 8 AA batteries 1 9 volt battery terminal 1 coaxial power plug 1 12 volt AA battery holder Shrink tube Slip the shrink tube over the wires of the 9 volt battery terminal and heat to shrink. Unscrew the collar of the coaxial power plug and slip it over the wire of the 9 volt battery terminal. Then solder the red wire to the center tab of the coaxial cable connector and the black wire to the outer tab and screw the collar back in place. Place the 8 AA batteries in the battery holder, clip the 9 volt battery terminal to the holder, and plug it into the oscilloscope and watch it boot up.

 Step 11: And We Are Done