Using analogRead() with ATtiny85

analogattiny85ledpotentiometer

I'm new the ATtiny series of Atmel MCUs and I've been trying to build a DC-DC boost converter with an ATtiny85-20PU recently.

To get started I've been trying to control the brightness of two LEDs by mapping the readings obtained using two 1k potentiometers. However only one LED responded and the other LED stays OFF the whole time.

So I did a minimal test and found out that whenever I try to use PB4 or PB2 to obtain an analogRead, it doesn't work for some reason. I'm able to get an analogRead only from PB3. The datasheet says that PB2, PB3 and PB4 are ADC channels

I'm using my Arduino UNO as ISP to program the ATtiny85 and I'm uploading the code using the Arduino IDE. I've tried looking up the datasheet and I was particularly going through the data given on the ADC unit and tried using the following.

According to the datasheet,

17.13.1 ADMUX – ADC Multiplexer Selection Register

• Bits 3:0 – MUX[3:0]: Analog Channel and Gain Selection Bits

The value of these bits selects which combination of analog inputs are
connected to the ADC.

So I tried including this in my setup,

ADMUX |= (6<<MUX0); #  this was  the bit configuration given for using PB3 and PB4 as the input channels

but had no luck.

This is my code:

int feedbackPin = 2; //Using 2 or 4 won't work.Only 3 works
int gatePin2 = 1;

void setup() {

pinMode(feedbackPin,INPUT);
pinMode(gatePin2,OUTPUT);

}

void loop() {

int v1 = analogRead(feedbackPin);
int del2 = map(v1,0,1023,0,255);
  analogWrite(gatePin2,del2);

}

I would appreciate any help in setting up the two analogReads correctly.

Best Answer

The analog and digital pin numbers are not the same.

PB3 is analog pin 3, that's why it works.

PB2 is analog pin 1.

PB4 is analog pin 2.

Related Solutions

Electrical – Should I use an LP2953 to power an ATTiny85 with a 12v battery

Unfortunately a linear regulator is a linear regulator - it drops the excess voltage and dissipates power as heat ... so just like the 7805 you had, the LP2953 is still a linear regulator.
12V in to 5V out makes it never much more than about 40% efficient, so however much power your ATTiny is using - 1.5x that is being wasted as heat in the regulator.
You could improve the regulator efficiency and reduce wastage significantly by using a DC-DC switch-mode regulator instead. They're more complicated to build from scratch, but ready-made modules are available - some are even drop-in replacements for the 3-pin 78xx linear regulators.
Chose the right one and you should easily get 80% or better efficiency from it.

Electronic – arduino – Missed Interrupt Problem with Attiny85

You go to sleep unconditionally in every iteration of loop(). That's not what you want. The way your code is now, you'll miss every wake up event that happens while your normal program code runs.

Your code spends most of the time delaying inside flash(). And the controller goes to sleep after flash() is done. Always. This means that whenever a wake up event occurrs while the LED is flashing, it will not cause a wake up. That's just because the interrupt occurred and was serviced before you went to sleep.

Have a look at the example in the avr-libc docs here.

Your code should look like this:

void loop(){

  cli(); // Disable interrupts to avoid race condition.

  if ( !resetEsp ) {
    // Only go to sleep if we have nothing to do right now.
    // Safe(*) code from the example in avr-libc:
    sleep_enable();
    sei();
    sleep_cpu();
    sleep_disable();    
  } else {
    sei(); // Can go on processing IRQs.
  }

  if (resetEsp) {

    cli();

    resetEsp = false; // clear the flags
    resetEnabled = false;

    sei();

    digitalWrite(pinRST, LOW); // reset the ESP
    delayMicroseconds(240);
    digitalWrite(pinRST, HIGH); // let the ESP Boot    
    flash(10, 50); // flash the led fast to show we're waking the ESP

  } else if (resetEnabled) {
    flash(10, 500);  // mostly never get here
  } else {
    flash(2, 500);   // these are the flashes I see most of the time
  }

}

The point here is that we disable all interrupts while we check to see if we want to go to sleep. This way, we make sure that no interrupt can happen after we checked but before we actually sleep. Is is crucial, however, that we enable interrupts again just before going to sleep, or we will never be woken up again.

Also, @jms is right in stating that you have another potential race codition when resetting your flags, so include some cli/sei there too.

set_sleep_mode(SLEEP_MODE_PWR_DOWN); can go into setup(). And if you're not controlling spacecraft the same goes for sleep_enable();, while omitting sleep_disable(); completely.

(*) The code labelled "safe" above is not absolutely bullet-proof because, in theory, during optimization the compiler could decide to reorder some instructions so that sei() and sleep_cpu() could end up not being in direct sequence. To be absolutely safe, check the generated assembler code (gcc -save-temps), or just write the reqired instructions as inline assembler yourself. (Can be as simple as asm volatile (" sei \r\n sleep \r\n " :::);.)

Best Answer

Related Solutions

Electrical – Should I use an LP2953 to power an ATTiny85 with a 12v battery

Electronic – arduino – Missed Interrupt Problem with Attiny85

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