Reading Temperature with AVR ADC The Atmega32 comes with a 10-bit, 8 channel inbuilt Ananlog to Digital Convertor (ADC). We will set it up and read temperature from LM35 and light with a simple (light dependent Resistor)LDR. I want to use an ATmega32 ADC in its 4 channel single-ended mode to convert four analog signals into digital (one at a time). I have written the C code but what I cannot figure out is what I should do with the ground pins of those four analog signals. Hard drive low level partition program for mac. I have no good knowledge about ADC conversion. At my projects i just can use only 1 channel ADC on ATmega32, but actually i want to use 4 channel ADC in the same time. Please help me how to use 4 channel ADC? Product FeaturesEASY TO CONNECT: With the kwmobile USB to TTL UART Converter you can easily connect your devices such as microcontroller or an Arduino to a PC module.MODULE INCLUDED: Along with the USB to TTL converter you also will receive an Atmega328 module.WITHOUT POWER CORD: The kwmobile USB to TTL converter does not need an [].
This tutorial is about ADC in AVR ATmega32A Microcontroller. ADC stands for analog to digital converter which allows us to interact with physical world. Almost all microcontrollers come’s with built-in circuitry of ADC. ADC allows us to read data from sensor using microcontroller. This way we could able to control, sense and communicate with real world data. Let’s get into little more technical. ADC in AVR ATmega32A Microcontroller is multiplexed with PORTA that means ADC channel are shared with PORTA. The ADC can be operated in single conversion mode and free running mode. In single conversion mode the ADC does the conversion and then stop. While in free running, it used to convert continuously. It does a conversion and start next conversion immediately after that.
How ADC Works?
In real world example, every sensor senses physical parameters (voltage, temperature or pressure etc.) and converts it into equivalent analog signal. But for efficient and ease of signal processing, this analog signal is converted into a equivalent digital value using analog to digital converter. This digital value is then fed into microcontrollers ADC featured pin.
The ADC of AVR has 8 channel and 10-bit resolution
8-channel: This means there are 8 ADC pins are multiplexed together. We can see those pins named as PA0, PA1….PA7. 10-bit Resolution: This means there are 2^10=1024 steps/counts.
Suppose we use 5V reference. In this case any analog value in between 0V and 5V is converted into its equivalent ADC value. The 0-5V range is divided into 2^10=1024 steps. Using the default reference voltage of 5v and this voltage is converted to a 10 bits value, the resolution of each bit is 5v/1023 = 4.88mV for each consecutive value, but imagine that you have an analog accelerometer, those are almost always 3.3v part, so if you used the 5v reference you would have 5 – 3.3 = 1.7v of unused values and also a reduced resolution, now let’s see what is the resolution if you used an 3.3v reference voltage 3.3/1023 = 3.22mV for each consecutive value, so it’s a gain in resolution and you would be able to use the full range of the ADC.
The internal ADC can also be used in an 8-bit mode, where only the most significant 8 bits of the full 10 bits resolution are used, this might be useful when working in noisy environments and you only need 8 bits resolution, using this mode is a plus because you don’t need to spend extra time shifting the full 10 bits result into an 8 bits.
Powerpoint download for mac. Let me introduce you something which is important to know that. As our chip is being feed with 5v we can plug any signal that we want to the ADC input pins if the signal is inside the 0-5v range, above or below that and the ADC circuitry will be damaged forever and you might even destroy the whole chip. We can also change(given that its always below the Vcc of chip) the maximum voltage that the ADC uses, for that you can put your desired max voltage(it’s called the reference voltage and it’s against this voltage that all analog to digital conversions are done) in the Aref pin, that is pin 32 of the DIP package and then configure the ADC in software to use that voltage reference, I will not explain this in this tutorial, but if you have doubts just shoot a question.
Let’s understand ADC Prescaler and ADC Register:
ADC PRESCALER
The ADC needs a clock pulse to do its conversion. This clock is generated by system clock by dividing it to get smaller frequency. The ADC requires a frequency between 50 KHz to 200 KHz. At higher frequency the conversion will be fast while at lower frequency conversion happens to be slow and accurate. First system frequency can be set to any value by their user. So the Prescaler is produces acceptable frequency for ADC from any system clock frequency. System clock can be divided by 2, 4, 16, 32, 64, and 128 by setting prescaler.
The ADC needs a clock pulse to do its conversion. This clock is generated by system clock by dividing it to get smaller frequency. The ADC requires a frequency between 50 KHz to 200 KHz. At higher frequency the conversion will be fast while at lower frequency conversion happens to be slow and accurate. First system frequency can be set to any value by their user. So the Prescaler is produces acceptable frequency for ADC from any system clock frequency. System clock can be divided by 2, 4, 16, 32, 64, and 128 by setting prescaler.
ADC REGISTERS
As we know registers are related to particular peripheral module (like ADC, Timer, and USART etc.) provides the communication link between CPU & peripheral. You can configure ADC according to your need using these registers and also you can get conversion result in appropriate register.
As we know registers are related to particular peripheral module (like ADC, Timer, and USART etc.) provides the communication link between CPU & peripheral. You can configure ADC according to your need using these registers and also you can get conversion result in appropriate register.
- ADC Multiplexer Selection Register- ADMUX
- ADC Control & Status Register- ADCSRA
- ADC Data Register- ADCL and ADCH
ADC Registers | Functions |
ADMUX | For selecting reference voltage and input channel |
ADCSRA | It represent status of ADC & also use for controlling it |
ADCL/ADCH | For collection of final result of conversion |
Let’s start by doing a simple test program so we can see our ADC in action. For this our atmega will read an 10Kohm POT connected to pin 0 of PORT A, that is the PA0 pin of ATmega32A, and the read value of POT will be displayed on serial terminal of PC. We’ll use USART Code Libraries for serial communication.
CONNECTIONS: ADC in AVR ATmega32A Microcontroller
The pot will be connected as shown in following schematic:
Please make sure to connect 16 MHz external crystal to ATmega32A microcontroller and do not forget to burn fuse bits after loading hex file into ATmega. Fuse bits are LFUSE: 0xFF HFUSE: 0x99. If in case you have any question, just write into comment section and we’ll help you out.
To make use the ADC in AVR ATmega32A Microcontroller. We have to perform some steps. Here is pseudo-code and this is what we need to do:
- Configure ADC
- Turn ON ADC
- Start ADC Conversion
- Read ADC value from ADC Data Register
Here is complete C Program to use ADC in AVR ATmega32A Microcontroller. Later on in this tutorial we’ll slice down program into several pieces to get more inside view.
First few lines represent some standard includes that we’ll be using while structuring our code. If you compare code from previous tutorial you’ll find lots of similarities. Here we’ll only discuss functions which are added into previous project. I recommend you to grab a datasheet and jump right on Chapter:22 and Page No: 223. Apart from that in main function.
First we need to provide a clock to the ADC, and as we have seen before this signal as a maximum recommended value and this clock is generated using prescaler, so let’s first setup our prescaler. This is configured in the ADCSRA register and the bits that are related to the prescaler settings are ADPS2, ADPS1 and ADPS0, you can see on page no: 226 the possible values for the prescaler are 2, 4, 8, 16, 32, 64 and 128, as we are running at 16Mhz we will use the 128 prescaler so our ADC clock will be of 125Khz (16000000/128= 125 Khz), to set this value we need to set the three ADPS bits to 1.
Now we will configure the voltage reference that our ADC will use, in this tutorial we will use the voltage that is also used to power the rest of our ATmega (+5v), with a external capacitor connected to AVCC pin. The reference voltage source is configured in the ADMUX register with the REFS0 and REFS1 bits. In our case we will make REFS0 bit to 1, it’s also in the ADMUX register that we can select which channel will be used to perform an analog to digital conversion, this is selected using the MUX3 to MUX0 bits, in this example we’ll not touch this bits as we are reading from channel 0 and all the bits in the registers are in the 0 state when we power up our ATmega.
Now our ADC is almost setup, we just need to turn it on (because by default it’s turned off so the micro-controller consumes less current), and for that we put the ADEN bit at 1 in the ADCSRA register. Remaining things are well commented into code itself.
Now here in this function we have to select the ADC input channel. In this example we’re going to read data from channel 0 which is PA0 pin of ATmega chip. Bootcamp windows 7 mac download. It can be done by setting or clearing the MUX4, MUX3, MUX2, MUX1 and MUX0 bits in the ADMUX register, the mapping between the MUX values and the selected channel is shown in this table:
MUX4 | MUX3 | MUX2 | MUX1 | MUX0 | Pin that will be read |
0 | 0 | 0 | 0 | 0 | PORTA0 Analog 0 |
0 | 0 | 0 | 0 | 1 | PORTA1 Analog 1 |
0 | 0 | 0 | 1 | 1 | PORTA2 Analog 2 |
0 | 0 | 0 | 0 | 0 | PORTA3 Analog3 |
0 | 0 | 1 | 0 | 0 | PORTA4 Analog 4 |
0 | 0 | 1 | 0 | 1 | PORTA5 Analog 5 |
0 | 0 | 1 | 1 | 0 | PORTA6 Analog 6 |
0 | 0 | 1 | 1 | 1 | PORTA7 Analog 7 |
when running in single conversion mode there are some new things that we must check, as the ADC clock is rather slow (125Khz compared to the 16Mhz that the chip is running) and each conversion takes 13 cycles of that 125Khz clock when we read the ADC we start a new single conversion and we need to wait until it’s done, to do this we check the bit ADSC until its cleared, when its cleared the conversion is done, and as we are doing single conversions we don’t need to mess with the ADTS and ADATE bits.
The code is still easy to read and understand, and now we have two handy functions that you can just copy and paste into your projects and read the ADC, the number that you pass to the read_adc(). It’s also the pin number from PORTA, so analog channel 0 is in PORTA0 and can be read using read_adc(0). The remaining setting is well commented in code itself and self explanatory.
You may wonder what is ADCW? Where does it come from? Its AVR LIBC function which supported by most of avr-gcc compilers, where we get result of ADC conversion. This could be handy instead of shifting bits to get 10 bit result from ADCH and ADCL. These are ADC Data Registers.
In never ending loop We’ll read the ADC converted value, and this has done using simple function read_adc(0). In order to convert the 10 bits ADC value to a readable number string we need to use a function called ITOA(stands for Integer TO ASCII) this function takes 3 input parameters, one is the value that we want to convert, this can be an uint8_t, uint16_t, int, and other similar types of integer variables, other of the input parameters is the base for where we want to convert, 2 to convert to binary, 8 for octal, 10 for decimal, and 16 for hexadecimal, and finally a small array that will be the output string plus the NULL string terminator, this output array must have at least space for the maximum number of chars that our number as plus one for the NULL, so as we are using 10 bits values from the ADC, this means that our maximum value is 2^10-1 = 1023, so we can have a maximum of 4 numbers plus the terminator so we need an array with space for 5 chars. Also, itoa is one of the standard functions of C, and thus it is located in the stdlib.h header and that header must be included so the compiler doesn’t complain.
When we compile and download output file to AVR ATmega32A (Make sure to set fuse bits). We’ll get ADC output on serial terminal of PC. Here is output from our project.
We hope you will find this tutorial educational and entertaining to use ADC in AVR ATmega32A Microcontroller. If you have any question then post into comment section of website.
Using LM35 Sensor and Atmega32 ADC to measure Temperature
Analog to digital conversion is generally needed whenever we deal with a sensor that produces an analog output (for example: LM35 temperature sensor), which is the case for a wide range of sensors. When dealing with such sensors we have to convert the analog signal coming out of them into digital words of ones and zeros so that our microcontroller can process it and make decisions based on it. In order to do that we need a device called an ADC (Analog to Digital Converter) and fortunately, many controllers now have this device built-in.
In this article, we shall learn about using the ADC of the Atmega32 to convert an analog signal to a digital one. As an example of an analog signal, we shall use the output signal coming out of the LM35 temperature sensor. By the end of this article, we will be able to make a simple fire alarmthat triggers a buzzer when the temperature exceeds a certain limit (60 Celsius degrees as an example).
ADC Reference Voltage
The reference voltage is the maximum voltage you are expecting to receive from the sensor on the input channel of the ADC. In Atmega32 you can use one of three sources for the reference voltage:
- An internal voltage from within the Atmega32 MCU. This voltage is set to 2.56V and cannot be changed.
- The AVCC pin can be your reference voltage, but this pin must be connected to the VCC and in this case, your reference voltage is the VCC
- Finally, you can use your own customized reference voltage by connecting a voltage source that has the same value as the reference voltage you want to the pin AREF (pin32).
Choosing between these three sources of reference voltage happens while configuring the ADMUX Lanscan for mac os x. register as we will explain later in this article. We will use the internal voltage option.
![Download Atmega Adc Conversion Time For Mac Download Atmega Adc Conversion Time For Mac](/uploads/1/2/6/1/126143172/939814689.jpg)
Hardware Requirements:
Before using the ADC of the Atmeg32 there are a few hardware connections required in the circuit so that you can get the best results:
- You should make sure that pins (VCC & AVCC) that are pins (10 & 30) are connected. This is because the ADC gets its power supply from the AVCC pin.
- If conversion accuracy is critical all the time, it is preferable that you connect a coil between the 2 pins and a capacitor between AVCC and GND. These 2 connections make the supply voltage of the ADC more stable and not easily fluctuated by noise.
- Also, it is preferable to connect a capacitor between AREF and GND so that the reference voltage of the ADC is more stable and not affected by noise. (Even if you choose to use the internal voltage or the AVCC)
- If you are going to use an external reference voltage, then you should connect it to the AREF pin. In this article, we will use the internal reference voltage so we will not need this step.
Atmega32 ADC Input Channels
https://exlutama.tistory.com/6. ADC of the Atmega32 can accept inputs from up to eight channels. This means that you can connect up to eight analog input signals to the Atmega32 ADC, but at each conversion, only one channel input is converted. So, at each conversion, you should first choose the input channel to convert before starting the conversion. This is also done in the ADMUX register.
Adc Conversion Time Formula
The input channels are multiplexed over the pins of port A of the ATmega32. These are the pins (33 to 40) Photoshop elements 10 mac download.
LM35DZ
LM35D is a temperature sensor Download zoosk chat for mac. of the LM35 temperature sensors family. It has 3 pins assigned as demonstrated in the below diagram. Where Vs is connected to the high voltage (VCC), GND is connected to GND and Vout is connected to the Input channel of the Atmega32 ADC
Important note: The pin-out diagram above (which is the same of the datasheet) is showing the sensor pin-out from the bottom view. So take care not to connect the sensor in reversed pin order.
The LM35 output voltage is linearly proportional to the temperature. It represents each 1 Celsius degree by 10 mV, so that if the temperature is 20 Celsius degrees, then the output voltage of the LM35 will be (20*10mV=200mV).
When the LM35 is connected as explained above it can detect temperatures between 2 and 150 Celsius degrees which means that the maximum output voltage will be (150*10mV=1500mV=1.5V). This means that we should use a reference voltage of 1.5V for best accuracy. However, for simplicity we can use the internal voltage (2.56V) and this is what we shall do in this article.
Temperature Calculation
The Atmega32 ADC has a resolution of 10 bits, which means that the output of the ADC will be a 10 bits binary word. This also means that the maximum output of the ADC will be the binary 1111.1111.11 that corresponds to a value of 1023 in decimal.
Now, as the maximum output of the ADC is 1023 and the maximum input is 2.56 (The Reference Voltage), then we can calculate the corresponding ADC output to an input of 10mV using the below equation:
So, each 10mV will cause the ADC to output a value of 4, and as 10mV corresponds to 1 Celsius degree, then each Celsius degree will cause the ADC to output a value of 4. So, if the temperature is 20 Celsius degrees, the output of the ADC will be (20*4=80) and in binary this is (0001.0100.00). We will read this value from the ADCH and ADCL registers as we will explain.
So, as a conclusion in our case, we can calculate the temperature value from the ADC output using this equation:
So, as a conclusion in our case, we can calculate the temperature value from the ADC output using this equation:
Software Requirements
Now, let’s get to the ADC Software configuration on the Atmega32
To enable the Analog to Digital Converter on Atmeg32 we need to do the following steps: https://heavytaste157.weebly.com/pod-farm-free-version-download-for-mac.html.
- In the ADMUX Register (ADC Multiplexer Selection Register):
- Set both bits (REFS1 & REFS0) to one. This tells the Atmega32 to use the internal voltage of 2.56 as a reference voltage.
- Clear the ADLAR bit to Zero. This will left adjust the ADC output (will be explained later in reading the ADC output)
- Choose the ADC input channel by setting the value of the 5 bits (MUX0…MUX4). In this article, we will clear them all to zero to choose the first input channel. This channel is the first pin in port A which is pin 40 of the Atmega32 IC. If you want to use another channel, check the below table to know the proper value for these bits.
MUX0 … MUX4 | ADC input Channel |
00000 | ADC0 |
00001 | ADC1 |
00010 | ADC2 |
00011 | ADC3 |
00100 | ADC4 |
00101 | ADC5 |
00110 | ADC6 |
00111 | ADC7 |
ADMUX Register | |||||||
REFS1 | REFS0 | ADLAR | MUX4 | MUX3 | MUX2 | MUX1 | MUX0 |
1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
- In the ADCSRA Register (ADC Status Register A):
- Set bit ADEN to1. This enables the ADC.
- The ADC module needs a clock to work and it takes this clock from the MCU clock. However, the MCU clock is divided by a factor before it is fed to the ADC. This factor is determined by the bits (ADPS2, ADPS1, ADPS0) in the ADCSRA register. In this article, we will set the three bits to 1 so that the division factor is 128. If you want to use another division factor, check the below table for the proper value of these bits.
ADPS2 | ADPS1 | ADPS0 | Division Factor |
0 | 0 | 0 | 2 |
0 | 0 | 1 | 2 |
0 | 1 | 0 | 4 |
0 | 1 | 1 | 8 |
1 | 0 | 0 | 16 |
1 | 0 | 1 | 32 |
1 | 1 | 0 | 64 |
1 | 1 | 1 | 128 |
ADCSRA Register | |||||||
ADEN | ADSC | ADATE | ADIF | ADIE | ADPS2 | ADPS1 | ADPS0 |
1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 |
Starting conversion and reading the ADC output
To start an analog to digital signal conversion, we set the 6th bit in ADCSRA (ADSC bit) to one. The ADC starts reading the analog signal immediately from the input channel (specified in ADMUX as explained above) and converts it to a digital 10-bit word. After finishing the conversion, the ADSC bit is cleared to zero again and the ADC module writes the output of the conversion (10-bits) in two registers named ADCH & ADCL. The bits are organized as demonstrated in the below figures.
Note the difference between ADLAR=0 and ADLAR=1. In this article, we had set ADLAR=0 in the ADMUX register.
If ADLAR=0:
– | – | – | – | – | – | ADC9 | ADC8 | ADCH |
ADC7 | ADC6 | ADC5 | ADC4 | ADC3 | ADC2 | ADC1 | ADC0 | ADCL |
If ADLAR=1:
ADC9 | ADC8 | ADC7 | ADC6 | ADC5 | ADC4 | ADC3 | ADC2 | ADCH |
ADC1 | ADC0 | – | – | – | – | – | – | ADCL |
When reading the ADC output, we should read ADCL first then read ADCH. This is because reading ADCL, informs the ADC module that a read process is in progress and so no conversions happen until the ADCH is read as well.
In our program, we will convert the output of the LM35 from analog to digital using the first ADC channel, we will turn on a buzzer that is connected to pin5 in port D when the temperature exceeds 60 Celsius degrees.
Below is the schematic, program code, pictures of the circuit and a video for the demonstration.
![Download Atmega Adc Conversion Time For Mac Download Atmega Adc Conversion Time For Mac](/uploads/1/2/6/1/126143172/230802444.jpg)
Circuit Diagram
Circuit Schematic – LM35 to AVR Atmega32
Program/Code
Output Photograph
I implemented this circuit on my AVR development board. If you have any doubts, please feel free to ask in the comments section.
Demonstration Video
Adc Conversion Time
I hope you all enjoyed my tutorial!