AVR Freaks

Arduino has a really nice "MAP" function that is useful for scaling one range to another:

ex. map( 0, 1023, 3, 98);    // maps adc range 0-1023 to pwm range 3-98

Source code for this function is easy to find using google.

Jim

LOL -- while we can see that OP doesn't have a good grasp of the situation, from time-to-time over the years I've chosen fixed-TOP 8-/9-/10-bit PWM in production apps.  It eliminates picking a TOP register and in some cases makes for a trivial yet useful transfer function.

He appears to be using mode 14. So ICR1 sets TOP - that is the PWM frequency, not the duty cycle. In mode14 OCR1A sets the duty cycle of the pulse on OC1A and OCR1B sets the duty cycle of the pulse on OC1B. So to vary the frequency (and also the couting range of the timer) he should vary ICR1 and to modulate the pulses he should change OCR1A / OCR1B.

You do however highlight the fact that he sets:

    ICR1 = 50; // Frequentie

So setting OCR1A values 0..1023 is not going to work as the majority of the range is beyond the end of the timer's counting range. So he actually needs to map 0..1023 from the ADC to 0..49 that the counter uses. That would seem to involve a division by 20.48. Wonder why he chose to set ICR1 to just 50 ?? Sure it's a very high PWM frequency but why? Anyway he needs:

   OCR1A = dutyCycle / 20.48;

as things stand at present. But life would be much simpler with:

    ICR1 = 1024; // Give timer same counting range as ADC readings for 1:1 mapping

in that case

   OCR1A = dutyCycle;

really could be used.

Showing your actual code (as revised) will help us help you...

As these things go, the code looks OK at a first glance...

1)  Learn how to use the Code tages <> on the formatting toolbar to preserve formatting

2)  ...the below should be 1023 not 1024 but won't affect operation much

3)  From your attached .JPG we see a PWM frequency of about 2kHz.  Does that make sense with your setup?  Which pin of the AVR are you actually probing with Channel 2 of your logic analyzer?

4)  Show the connections to your potentiometer.  Which AVR pin is the wiper connected to?  When you probe right at that pin, what Voltage do you see?  Does it change when you turn the pot?

5)  You are getting a runt PWM duty cycle, so I'm guessing ADC counts of zero.  So now we need to ask about AVcc and AGnd connections, and the level on those pins.

5a)  Now we need to ask about connections and the level on the AREF pin.

Discussion on the above:  Are you sure your AVR is running at 8MHz?  The PWM period suggests 16MHz to me, which is the Arduino frequency, right?

Still waiting:

You've also been asked if a PWM frequency of 314 kHz is what you wanted.  Is it?

You said:

I do not need a certain frequency for my project, but I want to be able to arrange the duty cycle between ~ 3 and 98%.

But that's not good enough.  Is a 1 Hz signal alright?  What about a 31.25 kHz signal?  Or an 80 kHz signal?  How about 0.0001 Hz?

"I want to get from New York City to Los Angeles.  It doesn't matter how long it takes."

Ok, if you walk 8 hours a day, 5 days a week, starting now, you'll get there in time for International Youth Day in August.   Is that OK?

You must decide what range of frequencies will be suitable for your needs.

Ok, lets say frequency between 30 and 150 kHz? Is that alright?

30 Hz?  Or 30 kHz?

e.g. ~ 3% to 98%

With what degree of precision?  That is, how fine a step size do you need?  Is 5% per step sufficient?:

• 3%
• 8%
• 13%
• .
• .
• .
• 88%
• 93%
• 98%

Or do you need 1%?  Better than 1%?

3% and 98% seem fairly arbitrary and specific.  Is this to control a specific device?  Where do these numbers come from?

I'd like to see the generated code, such as the .LSS file.  And perhaps the build log and the ISP log -- is the right file getting to your target chip?

Although, you can be forgiven for not doing so, since a site upgrade earlier today broke the code editor.

#define F_CPU    8000000UL
#include <avr/io.h>
#include <avr/interrupt.h>

volatile uint16_t dutyCycle;


int main(void) {

  DDRB = (1 << PORTB1);
  TCCR1A |= (1 << COM1A1) | (1 << COM1A0) | (1 << WGM11);
  TCCR1B |= (1<<WGM13) | (1 << WGM12) | (1 << CS11);
  ICR1 = 1023;
  //OCR1A = 6;
  //OCR1B = 250;
  TIMSK1 = (1 << TOIE1);
  setupADC();
  sei();
  while(1) {}
  
}


void setupADC() {
  ADMUX = (1 << REFS0) | (1 << REFS0) | (1 << MUX0) | (1 << MUX2);
  ADCSRA = (1 << ADEN) | (1 << ADIE) | (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0);
  DIDR0 = (1 << ADC5D);
  startConversion();
}


void startConversion() {
  ADCSRA |= (1 << ADSC);
}


ISR(TIMER1_OVF_vect) {
  OCR1A = dutyCycle;
}


ISR(ADC_vect) {
  dutyCycle = ADC;
  startConversion();
}

Although it does no harm, you've specified (1 << REFS0) twice.  Once is enough ;-)

Should I use OCR1A=6 and OCRB=250 with Timer1? But OCR1A is already used in the (Timer1_OVF_vect) what about this?

I think you've misunderstood.  With mode 14 on TIMER1, ICR1 sets the >>resolution<< of the timer, while OCR1A and OCR1B are used to set the duty cycle of the two outputs OC1A and OC1B, respectively.  They do not set minimums and maximums.

You've made PB1/OC1A and output, so you should use OCR1A, which you are.

I think you can do away with the TIMER1 overflow interrupt altogether (and refrain from enabling it with TOIE1), and assign the new value for OCR1A directly in the ADC.

Your schematic doesn't make much sense.  Why two variable resistors?  Why not just a potentiometer?:

assign the new value for OCR1A directly in the ADC --> how should I make this in the source?

Whoops that was supposed to say ADC_vect ISR.  What I mean is that you can assign the new value for OCR1A in the ADC ISR.  You don't need the timer ISR to do that.

The 1k 10 turn adjustment potentiometer serves as a pre-setting to set 2Vdc as bias, with another "potentiometer" this value should be 1Vdc

I'm not certain I understand.  Are you saying that the 1K pot needs to be adjusted such that when the sensor is 280 ohms (is that 'full'?), then the voltage of the resultant divider should be 2V, and when it is 65 ohms (is that empty), it should be 1V?  If not, then please say exactly what you mean.  Tell the range of voltages you want to see when the sensor swings from 65 ohms to 280 ohms.

This is what I mean by being specific when you state your requirements.  Here we are at post #40 and we are hardly any closer to answering your question than when this thread began.  Statement of the problem and the subsequent statement of the requirements for solving it are arguably the most important steps in any engineering endeavour.  I would argue that they are the most important steps in >>any<< human endeavour, technical or not.

Assuming I'm right and you want 1V-2V swing from the sensor, then there is a bit of arithmetic to do.  First we should try to determine the resistance needed on the 1K pot to achieve that range.

If:

• the 1K pot we call R2
• the 'full' voltage we call Vf
• the 'empty' voltage we call Ve
• the 'full' resistance of the sensor we call Rf
• the 'empty' resistance of the sensor we call Re

... then we have two equations:

Vf = (Vcc * Rf) / (Rf + R2)

Ve = (Vcc * Re) / (Re + R2)

Filling in known values, we get:

2 = (5 * 280) / (280 + R2)

1 = (5 * 65) / (65 + R2)

Solving the first:

             2 = 1400 / (280 + R2)

2 * (280 + R2) = 1400

     560 + 2R2 = 1400

           2R2 = 840

            R2 = 420

Now we do the same for the second:

      1 = (5 * 65) / (65 + R2)

      1 = 325 / (65 + R2)

65 + R2 = 325

     R2 = 260

So we see that it is not possible to set the 1K to a single value which will result in the voltage swing you require.  Either I have misunderstood what you've said, or your circuit is not adequate to the task.  You need another resistor 'below' the sensor:

         VCC
          ^
          |
          |
          |
         +-+/
         | /   R3
         |/|   1K
         / |
        /+-+
          |
ADC5------+
          |
         +-+/
         | /  Sensor
         |/|  65-280
         / |
        /+-+
          |
          |
          |
         +-+/
         | /   R1
         |/|   1K
         / |
        /+-+
          |
          |
          |
         GND

Now we have two new equations:

Vf = (Vcc * (R1 + Rf)) / (R1 + Rf + R3)

Ve = (Vcc * (R1 + Re)) / (R1 + Re + R3)

Filling in known values:

2 = (5 * (R1 + 280)) / (R1 + 280 + R3)

1 = (5 * (R1 + 65)) / (R1 + 65 + R3)

Solving the first for R3 w.r.t. R1:

                  2 = (5 * (R1 + 280)) / (R1 + 280 + R3)

2 * (R1 + 280 + R3) = 5 * (R1 + 280)

    2R1 + 560 + 2R3 = 5R1 + 1400

          2R1 + 2R3 = 5R1 + 840

                2R3 = 3R1 + 840

                 R3 = (3R1 + 840) / 2

Solving the second for R3 w.r.t. R1:

           1 = (5 * (R1 + 65)) / (R1 + 65 + R3)

R1 + 65 + R3 = 5R1 + 325

          R3 = 4R1 + 260

Now we combine the two to solve for R1:

4R1 + 260 = (3R1 + 840) / 2

8R1 + 520 = 3R1 + 840

      5R1 = 320

       R1 = 64

Now we plug our solved value for R1 back into one of the equations (it doesn't matter which) to solve for R3:

          R3 = 4R1 + 260

             = (4 * 64) + 260

             = 256 + 260

             = 516

We can verify our results by plugging those values in to each initial equation:

Vf = (Vcc * (R1 + Rf)) / (R1 + Rf + R3)

   = (5 * (64 + 280)) / (64 + 280 + 516)

   = (5 * 344) / 860

   = 1720 / 860

   = 2

Ve = (Vcc * (R1 + Re)) / (R1 + Re + R3)

   = (5 * (64 + 65)) / (64 + 65 + 516)

   = (5 * 129) / 645

   = 654 / 645

   = 1

So that seems to work.  In order to get the 1V-2V swing on ADC5, you'll want a 516 ohm resistor above the sensor, and a 64 ohm resistor below the sensor.  A good value for the top trimpot is 1K as you already have.  A good value for the bottom trim pot would be 100 ohms.

If this makes sense to you, you can move on to the code.  If I've misunderstood your requirements for the voltage range presented to ADC5 by your sensor voltage divider, then please set me straight.  You might also want to explain the rationale behind those requirements.  For instance (if I'm right) why do you require a 1V-2V range?  Is this a requirement given to you by your teacher with no explanation?  Or was an explanation provided to you?

I think I've done enough of your homework for you for today ;-)

You haven't answered my questions:

I'm not certain I understand.  Are you saying that the 1K pot needs to be adjusted such that when the sensor is 280 ohms (is that 'full'?), then the voltage of the resultant divider should be 2V, and when it is 65 ohms (is that empty), it should be 1V?  If not, then please say exactly what you mean.  Tell the range of voltages you want to see when the sensor swings from 65 ohms to 280 ohms.

If I've misunderstood your requirements for the voltage range presented to ADC5 by your sensor voltage divider, then please set me straight.  You might also want to explain the rationale behind those requirements.  For instance (if I'm right) why do you require a 1V-2V range?  Is this a requirement given to you by your teacher with no explanation?  Or was an explanation provided to you?

Once you nail down the range of voltages you want to see on ADC5, then we can determine what range of values you'll see from the ADC, and then create a transfer function which converts that range of values to the 3%-98% PWM values you want.

ADC max value = 409.6 and ADC min value = 122.88    because ADC=(Vin*1024)/Vref

How did you get 122.88 from a required range of 0.1V to 2.0V?

The higher number is right (although Cliff has pointed out you can't represent fraction numbers in an integer), but the lower number represents 0.6V, not 0.1V.

Cliff has explained it perfectly well.  And both Jim and I have even pointed out where you can find the source code which will completely solve your problem.  Jim even actually posted it here!  Why are you still working on this?

IF you expect the ADC to return a value no lower than 20, and

IF you expect the ADC to return a value no higher than 410, and

IF you want a minimum OCR1A value of 6 (2.73%), and

IF you want a maximum OCR1A value of 250 (98.05%), and

WERE you to use the Arduino map() function, then it would look like this:

OCR1A = map(ADC, 20, 410, 6, 250);

Since you're not using the Arduino environment, you can simply implement the same function in your own code.  Have you even >>looked<< at the source?

You will need to handle cases where the ADC value is outside the range you expect so that your device doesn't explode.  What happens if the sensor fails?  What happens if there is a short somewhere?

I will not open a random .docx file.  Post the text of it here instead.

???  Does everyone else know what that means?  Do you mean that you want a duty cycle greater than 99.9% ?  What duty cycle >>do<< you want?  For which input value?  What duty cycle are you getting now?

Define "doesn't work".  Start over and show schematic/connections.  Tell voltages >>right on the AVR pins<<.  Show a complete test program.  Tell language, toolchain, and build settings including optimization level.  Tell how you are testing.  Tell what you expect to happen; tell what >>is<< happening.

There is a reason for knowing each piece of information requested, to answer your query.

What answer is map() giving you?  For what input?

All that said, perhaps depending on your timer setup you are getting the "single pulse" PWM at 0.  You can't get full-on and full-off at the same time with Fast PWM on an AVR8.  If you want full-off then use inverted PWM at the expense of not being able to get full-on.

Be_logic,

You do understand what's happening when Joey does this?...

#define ADC_MIN 21
#define ADC_MAX 409
#define PWM_MIN 6
#define PWM_MAX 250

OCR1A = map(adc, ADC_MIN, ADC_MAX, PWM_MIN, PWM_MAX);

so in other words it's just:

OCR1A = map(adc, 21, 409, 6, 250);

So that's saying "here is an ADC reading in the "adc" variable, it will be somewhere between 21 and 409, now map the value to the range 6 to 250". So this can only ever set OCR1A to values between 6 and 250. It will set it to 6 when "adc" is 21 and set it to 250 when "adc" is 409. It will linearly scale all readings between 21..409 to be PWM values between 6 and 250.

If these limits for ADC readings or for PWM range do not match your actual implementation then change:

#define ADC_MIN 21
#define ADC_MAX 409
#define PWM_MIN 6
#define PWM_MAX 250

If you want an ADC reading of 0 to map to a PWM setting of 0 then perhaps:

#define ADC_MIN 0
#define ADC_MAX 409
#define PWM_MIN 0
#define PWM_MAX 250

All this is a long version of what Kartman said in #65

More generally you need to determine:

What is the reading of ADC at the minimum point  - set this as ADC_MIN

What is the reading of ADC at the maximum point - set this as ADC_MAX

What is the minimum PWM/OCR value you want at the "bottom end" - set this as PWM_MIN

What is the maximum PWM/OCR value you want at the "top end" - set this as PWM_MAX

Job done.

Ummmm...not necessarily:https://www.avrfreaks.net/commen...

[you answered in that thread as well]

Apparently, the message got through after many repeated attempts.

the frustrating part is that he dug up the old pertinent thread, which had the same symptoms and outlined the cause and solution.  Yet the discussion was ignored, and something to the effect of "what could be the problem and how can it be cured" was posted.  Similarly in this thread.

Also note that this looks wrong:

        // constrain

        if (adc < ADC_MIN)
        {
            adc = 0;

        }
        else if (adc > ADC_MAX)
        {
            adc = ADC_MAX;
        }

0 is not in the range ADC_MIN to ADC_MAX (unless you changed the values?) so you cannot set this as the lower bound or the map() function will not work. You should have:

        // constrain

        if (adc < ADC_MIN)
        {
            adc = ADC_MIN;

        }
        else if (adc > ADC_MAX)
        {
            adc = ADC_MAX;
        }

It seems to me that you are just throwing code at your C editor without actually thinking about what you are doing. Software authoring should be a case of careful design followed by easy implementation. You seem to be skipping the design steps. If this is because you don't understand something then ask questions don't just guess at things randomly.

EDIT: oh this is ludicrous - I just read back through the thread as I can't believe it's taken 75 posts to get here and I found in #63 that Joey already gave you the correct code and you have actually CHANGED IT?!?! If you don't know what you are doing then don't just throw random ideas at the thing.

I already told you in #70 how to map to PWM_MIN=0 and that is by adjusting the four #define's - which bit of that sentence is it that you can't wrap your brain around??

This is like pulling teeth. No one here is psychic (AFAIK) so we can't possibly know what you have changed the MIN/MAX values to if you don't show us?!?!

And have you confirmed that if you simply set OCR1A to 0 or 115 it changes the duty "full scale"? Have you also confirmed that your ADC really does provide readings of 0 and 438 at either end of the Pot travel?

Just as an aside, likely not related to your issue... One subtle change needed in the code I posted in #63:

    // Constrain.
    if (adc <= ADC_MIN) {
      adc = ADC_MIN;
    }
    else if (adc > ADC_MAX) {
      adc = ADC_MAX;
    }

This will avoid a warning when ADC_MIN is defined as 0.

Unless you're using -Werror (which, you should, by the way), the code in #63 will still build.  If you >>are<< using -Werror, >>and<< you failed to notice a failed build, it might explain why you're not seeing the results you're expecting i.e. the new code isn't actually making it onto the target.