35. Arduino for Production! AVR ADC How to use multiple channels on the analog to digital converter 

Using a bitwise mask to blankout the higher bits of ADMX helps keep the switch cases clear of unrelated bits : switch(ADMUX & 0x0F) { case 0x00 : // ... break; case 0x01 : // ... break; } These tutorial series are GRRRREAT ! Its about half a year I'm wandering around this MC topic ... Now I'm started the right way. Thanks !!

Very good tutorials man, I Gave myself a mini-project that was intended to help me with a much bigger project. I essentially ended up branching out to use ADC, LCD, PWM and USART. I created a Proteus ISIS simulation file with the schematic and hex code loaded on the "virtual" ATMEGA32. I used the USART aspect to send and receive data serially (async) via the RXD and TXD pins. The used Channel 0 of the ADC to read in analogue information from an LM35 Temperature sensor and used some signal conditioning to get the equivalent temperatures to send to the LCD. The ADC value was also used to modulate the power going to a motor/fan that changed speeds depending on the temperature. I printed all the data to the 20x4 LCD (Temperature, Duty cycle, etc.) With the help of this video, i figured out how to include a POT on another ADC channel and just displayed its ADC value to the LCD. **I have a few questions though: 1. How do you know what resolution to use when reading sensor data ? For example: Using the AVCC gives arguably the best full-scale resolution but for the ACCELEROMETER you said something about using the internal. Does that not low your accuracy and precision ? due to you not having a large enough resolution ? 2. Why do you always use "lowADC = ADCL" then "thenBitADC = ADCH

wow ur an angel

Thanks. That is a good comment. I will try that method to see if it improves.

Great I was going to ask for it :P thanks for all these tutorials. It help me getting back on microcontrollers

Hi Patrick! You can use the & operator to check the channel number in the ADMUX which is an easy way and need not to also check the REFS bits. Thanks a lot for making these interesting tutorials :)

@marcfeyzeau Very good idea. I will add annotations on the video to show this option.

@pcangeldust Yes, I will be doing the 4-bit interface very soon.

@pcangeldust You need to see the LCD tutorials where we construct that routine.

Thank you. very helpful.

Hey there. Even after this much time, these videos are still awesome! :D Just wanted to give you a heads up, and tell you that, just as ADCL and ADCH will give you the low and high results, and combining them will give you a 16 bit result, so will just ADC. ADC is mapped as a 16bit value, to the address of ADCL, and will therefore include the next 8 bits right after, which happens to be ADCH :) Take a look at iotnx5.h (might be different which header file your chip is referenced in, this is an attiny85)

Excellent

Thank you Sir problem solved.

@anajonesr Yh I went back and saw that I missed that thanks for your efforts, one question when will you do the 4-bit interface tutorial if you are still planning to do it?

Thanks for the tutorial! so if i wanted to use multiple inputs, I could do sensor1 = ADMUX | 0b0000001, sensor2 = ADMUX | 0b00000010 ? then that will assign the respective pins to a variable?

Super

so i followed this tutorial and adopted it to my project... trying to connect three sensors. however, i keep getting this error "error: expected identifier or '(' before numeric constant ISR(ADC_vect) //selecting between multiple adc channels" what could be the solution.

Hi Patrick, I have a problem about this topic. When I want to test the circuit, the microcontroller reset itself before going into the while loop, I don´t know if this problem is caused for a hardware or a software issue. I'm using an ATmega164P.

What program are you using to code?

Hum would be better to filter ADMUX into another variable to only keep the MUXs values and not have to change them if you change ADMUX at the setting. mux = ADMUX | 0b00011111; (0x1F) and do the switch with mux (case 1/ case 2 etc...) Thanks again for you work. this is great !

where did you get a send an interger to lcd, I thought you had to covert it to char and then send string

Hi. How do I make three input ADC Channel? for example 2 pot 1 temp sensor and 3 hall sensor ınput etc.. Thanks.

two ways: use an op amp or a voltage divider with 2 resistors if you don't need high acuracy.

Im getting error results if I switch between channels, I did not use ISR, but I manually waited until the ADSC bit is clear, I don't know how ISR made a difference. What could gone wrong?

I would probably be easier to adjust the 0-10v to 0-5v in the circuit.

@marcfeyzeau Great. Nice coincidence.

Yes, I meant that, how to accept 10v by discrete components and adjust it to max. 5v for AVR adc pin ? If I put voltage divider with two same value resistors (10K) than I will loose range from 0-5v on input , if I understand good ? O.o

How can I "expand" ADC "range" for voltage 0-10v ? :)

hey sir, do you need x and y table to read the value from the Accelerometer

i used your program to read two rotary pots....and it works thanks! ..i wished to modify it so that when one value is greater than the other then a certain led should glow..it tried various logics....using variables but am not getting the results...can you help?

On your conversion ,what is your refence value?i think the microcontroller need a range of values to ratio to the analog value

for two channels you can just ADMUX |= ( 1

Hello sir :D , if i may ask , what if i want to tie more than 2 sensors to the ADC in the video u said we go back and forth between the channels but how does that apply to three channels do i go one by one , and what if i want to make for some reason only pin 0 and pin 2 work as an analog pins what should i do in that case ? Thank u so much for your tutorials and your kindness.

Why messing with ADCL and ADCH, when C compiler take care of it as ADC. If you build assembler program, then it is your task. Else C compiler take care of everything else. Just: int value=ADC; .