Using PWM on atmega16

Things u need

1. A  MCU (atmega16 or atmega8)
2. A led and/or motor and/or dc fan.

Difficulty Level

Easy from application point of view, a bit typical from programming point of view.

Time Required

If you are using the code given my me, then 1/2 or 1 hour.

Concept

PWM means Pulse Width Modulation.

Before lettting you what does it mean, let mew ask you a simple question, How to regulate a motor's speed?

You may answer that using a variable resistance, but what if I need to do it by using programming. Here PWM comes in play. One more famous example is  How to show the dimming effect in a led. Again PWM the answer.

What PWM does is that instead of sending a continuous supply of voltage to load (led, motor, dc fan, etc) it sends the supply in PULSE , that’s why the process is called PULSE WIDTH MODULATION.

Now if we have to control the speed of motor or intensity of led then we have to control the WIDTH of the PULSE.

There are two things to learn to use PWM,

1. Timers
2. OCR register

There are two internal Timers in atmega8, T0 (pin6, D4) and T1 (pin11, D5) and in atmega16 also T0 (pin1, B0) and T1 (pin2, B1).

These timers once activated run continuously from 0 to 255 (8 bit) as long as the program runs.

There are 3 OCR registers in both atmega8 as well as atmega16.

In atmega8 pin15 is OC1A, pin16 is OC1B, pin17 is OC2.

In atmega16 pin18,19,21 are OC1A,OC1B and OC2 respectively.

The PULSE WIDTH is set by these OCR registers only.

The time upto which MCU will send supply depends on what is value of OCR register.

Suppose the value of OC1A is 128 then while the timer which is running is between 0-128 the MCU will send supply to pin19 (atmega16) or pin15 (atmega8)   and when its between 129-255 the MCU will not send supply to that pin, so the bottom line is that for exactly half time pin is getting the supply and for exactly half time the supply is off, so the effective voltage reduces from 5v to 2.5v. The motor will run slow , the led will dimmed.

Below is the code shown for using PWM

This will make the LED to glow from minimum intensity (OCR1A=0 ) and then the increases  upto highest intensity (OCR1A=255) . You can add delay to increase the time required to complete one cycle.

To get full code download the link.

Download this link which has the required Header Files (timer0.h,timer1.h,timer0.c,timer1.c).

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Measuring tempearture using LM35.

Things you Need

1. LM35 IC
2. Male & Female Burg-Stick (optional if using breadboard)
3. Solder wire & Soldering Iron
4. Connecting Wire

Time Needed

1-2  hour depending on how good & fast you are at soldering. If using breadboard to make temporary circuit it will hardly take an hour.

Difficulty Level

Easy :)

The pin configuration of LM35 is shown below.

Step 1:

Insert the female burg-stick to a small piece of PCB (I do so to make circuit more stable and durable) or insert in a breadboard. Then Solder it. Also insert the Male burg-stick and solder it.

Now insert the LM35 IC in that female stick.

Step 2 (If using AVR-KIT from BRiCS):

Connect pin1 of IC (VCC) to pin2 of stick, pin2 of IC (VOUT) to pin4 of stick, pin3 of IC (GND) to pin1 of stick.

Step 2 (If using BreadBoard):

Connect pin1 of IC (VCC) to VCC of MCU (pin10 in Atmega16,pin7 in Atmega8), pin2 of IC (VOUT) to any ADC pin (port-A in Atmega16, port-C in Atmega8) of MCU, pin3 of IC (GND) to GND of MCU (pin11 in Atmega16,pin8 in Atmega8).

Step 3:

Connect the stick directly to kit . Those using breadboard don’t need to anything.

Hardware part is done. :)

Coding & Concept:

Lm35 IC gives a linear output voltage in Degree Celsius.

There is rise of 10mV of output voltage for one degree rise in temperature. This means,

500 mv == 50°C       100 mv == 10°C     and so on.

Datasheet tells that it may measure tem[erature from -50°C to 150°C!!  :O

 We know that (I suppose :P) in avr MCU the ADC reading is in 10 bit, that means

1024 adc reading = 5 volt = 5000 mv = 500°C  (not measurable).
1 adc reading = 5/1024 = 0.0049 volt = 4.9 mv = 0.49°C
x adc reading = 0.0048828*x volt = (4.8828 * x )°C.

So we have our formula ready i.e. Temperature =   (4.8828 * adc_reading )°C.

The coding is shown below.

 For full code download this file.

Now lets see the output.

Ok but now how can I produce a high temperature, lets bring the soldering iron (which I left on) near the IC, It should increase the temperature.

See its working. It rised to 41°C from 31°C.

You can make this circuit on PCB also.

We can use two 7segment LEDs also to display the temp, it looks cool :)

To learn how to use 7segment LEDs please have a look on my post "How to interface 7segment LED with Microcontroller"  Link will be updated soon.

To learn "How to control a fan speed according to temperature variation" please  refer to my post "How to use PWM with Atmega-16" Link will be updated soon.

If you have any other idea about what else we can do with the temperaure from LM35 in other projects please let me know, I'll try to include it here.

Suggestions And Queries are most welcome. :)  

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Circuit Diagrams

The page is internally linked, so click on any link to go to that particular circuit-diagram.

1. L293d - Motor Driver IC
2. 7805 - Voltage Regulator ICC
3. LED display without using shift registerC
4. LED display using shift registerC
5. Keypad 4x4 [16 buttton]C
6. Keypad 7x4 [28 button]C
7. MT8870 - DTMF [Dual Tone Multi-Frequency]C
8. DS1307 - RTC [Real Time Clock]C
9. IR sensorC
10. Propeller/Spinning ClockC
11. Propeller Clock Using Motor & InteruptC
12. MCU to MCU Rx TxC
13. 
    

Interfacing L293D IC with Atmega-16 to drive two motors.

Interfacing LED display with Atmega-16 without shift register

Interfacing 7805 - Voltage Regulator IC with Atmega-16

CM8870/MT8870 [DTMF] IC 

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How to make a Propeller Display

Things U Need

1. 8 LEDs
2. 8-10 meter long wire
3. 11 Male Burg-Stick pins
4. A small dot-PCB (optional)
5. A wire-cutter (optional)
6. Soldering Iron & Solder Wire
7. AVR kit (Brics Students already have it) or a microcontroller+programmer+breadboard

Time Required

1-2 hours maximum.

Difficulty Level

Between easy-average.

Actually after reading this it'll be very easy to make your own propeller clock.

Step 1:

Take 8 leds and short the negative terminal of each led. If you want to make it easy then first insert every led in  a dot-PCB (first cut the PCB as shown in image). Make sure all leds are in same format (either +ve terminal upward or vice-versa). Now you can easily bend the -ve terminals of all leds  and solder them.

Step 2:

Cut the +ve terminals as shown in image, leave only 2mm approx. of terminal.

Step 3:

Take 8 wires each of 1 meter and solder each wire to each led's +ve terminal, and lastly tie the end with some wire so that the wires don't fly out when you are rotating them.

Step 4:

Take 11 male burg-stick pins, solder the 1st led's wire (starting from bottom) to 1st burg-stick pin, 2nd wire to 4th pin (yes leave 2 pins empty [only for BRiCS kit]) likewise other wires to remaining pins. Other Students can directly insert wires into breadboard (See the pins of ATMEGA-16, ATMEGA-8 first).

Step 5:

Now students having kit insert the pins into any port, others dont need to do anything else if you have already connected your MCU on breadboard to wires.

Construction part is over, isn't that was fast!

Now only programming part is left over

If you know the concept behind the working of propeller clock then skip to Step-6, else read this.

When the array of led is moving fast in circle then the leds which are blinking very fast gives a impression that some message is being printed because of Persistence of Vision (POV). 

Lets assume on time 't' the array is at 90 degree in air, all leds are glowing, after a milli sec later when the array displays a little in clockwise direction then lets say from top 4th led is glowing, similarly for 3 more times 4th led is glowing and 4th time again all led glows.
Can you guess what will happen?
You will see that letter 'H' being printed in air.

Step 6:

Produce the "decimal numbers" of the required message that you wish to print in air, by using excel if you dont know how to do it dont worry read this post "How To Use Excel To Generate Code For Propeller Clock & LED Display".

lets assume you wished to display a heart, the decimal code for heart is 6,15,31,62,124,62,31,15,6,0. You can guess how this works by seeing the image below or else read the above post "How to Use Excel..........".

The code will be:

char a[]={6, 15, 31, 62, 124, 62, 31, 15, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, i=0; 

// extra zeros so that two hearts dont overlap

for(i=0;i<=20;i++){

  PORTB=a[i]; _delay_ms(5); // if it flickers then use _delay_us(500) or even low.

}

To get complete .c file click download.

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Introduction to MCU [MicroController]- Atmega-16 & Atmega-8

There are many MCUs available in market.

Some famous are AVR, 8051, pic,ARM, etc

We'll be using atmega series (atmega-8, atmega-16,atmega-32,etc).

In atmega-16 there are 40 pins, 4 ports, PORTA, PORTB, PORTC, PORTD.Each port has 8 pins. So you got a total of 32 input/output pins. The rest 8 pins  are 2-VCC, 2-GND,2-XTAL (crystals) 1-AREF(reference),1-RESET. 

Each PORT has 3-registers, for e.g. port-A has PORTA, PINA, DDRA. 

Each register has 8 BITS, as you can see in the following image. By default all 8 BITS are zero.

Lets talk about port-A, same will be for others also.

NOTE: port-A & PORTA are different terms. Dont confuse between them.

The PORTA & DDRA registers are writable that means we can change there value by PORTA=8; or like any value between 0-255. But PINA register is not writable, we can only read from it.

Read from it? Wait a min.... I didn't got it.

We'll see it in a couple of minutes.

First you need to know that what is the role of DDRA register. Well you can see it as a switch, if any particular bit's value is one then the respected bit's of PORTA & PINA are shorted. It means the value of PORTA gets copied to PINA if DDRA is 1. 

If you don't know how PORTD=12 make bit 2 and bit 3 as 1 and rest 0 then you need to read this before going further.
Its an article on "How to use decimal and binary numbers to change values of ports of a Micro-Controller".

Link Broken? Post a comment, i'll renew it.

Now when you have read the above article then u may know whats the meaning of DDRB=69, so lets see how DDR register works.

Lets suppose we want to glow a LED.
To do that you have to connect it to any pin of MCU, then just make that pin 1 (ON).
Naa its not that simple, first you have to short the DDRB's bit 0 with PINB's bit 0.
For that use DDRB=1; before main() function.
Now connect the negative terminal of LED to ground of MCU, and make PORTB=1.
This will glow the LED.

If you want to glow all LEDs then what will you do?
The answer is simple

DDRB=255;
main(){
PORTB=255;
}

What you have to remember

If DDR register is so necessary then why not permanently set it to 255.

Well thats the thing you have to remember that before using any port in your program don't forget to make its DDR register to 255.

This will permanently short each bit of that particular port.   

Do you remember i said something "copy value from pin"

Yes, you can copy the value (High or Low) of any pin. In embedded systems 0 means 0v and 1 means 5v. So you can check whether a pin is at High or Low state.

Why i need to check the value of any pin?

Suppose you are making some project in which you want that if power comes something shoud happen and if power goes off then some other thing should happen,

or simple you want to make a LFR (Line following Robot) or "DTMF controlled Robot" that requires to read the values from pin then you will need this.

Caution !

Are you getting any clue from these images what i want to say?
Yes, if you are shorting PORT and PIN then dont give input as it may cause short-circuit.

What you have to remember

If you want to take input from a pin then set DDRB=0; and if you want to give output to a pin then set DDRB=255; .

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Installing Eclipse- - Complete Walk-through

What is ECLIPSE?

The software that I'll be using is eclipse.

It’s a freeware. The standard version that is available on net does not has that "AVR plug-in" that is required to upload program in a microcontroller.

You can download the required version of eclipse from here.

eclipse.7z     Link Broken? Post a comment, i'll renew it.

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A Word From Writer.......

Hey guyz, 

My name is Harendra Singh, i am a CSE student at IIITDM JABALPUR in 2nd yr. I have done course in Robotics & Advanced Embedded System from BRiCS and also taught there.

This blog is essentially for the starters in robotics, the later sections will include posts for advanced robotics also. This blog will help you in the basic understanding of the embedded system. I will post the detailed tutorial on all topics. Feel free to request your queries or any other help. :)
Before taking any tutorial please go through these two basic tutorials-

1. Installation of Eclipse Software needed to program Micro-controller

2. Intro to Atmega-16        Introduction to Basics of Microcontroller

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