Generating good Signal with 60 kHz not possible?

Projects Programming
1

I want to generate a signal with about 50 to 60 kHz. I tried it with severall microprovessors:
Arduino is too slow, ESP32 with 240 MHz is good, Teensy 4.0 is better...
My problem is that even when I can generate the signal it is not stable. I think there are interrupts behind which I cannot stop. I already use:

WiFi.disconnect(true);
WiFi.mode(WIFI_OFF);
btStop(); 
setCpuFrequencyMhz(240); 
noInterrupts();

I've tried to make the signal in a separate processor-core. It doesn't help.
I've also tried to se interrupts to make the signal: Doesn't help.
I made it with a separate task (with high priority): Doesn't help.

Is there a way to make such a signal stable with a code like this (or anything else?):

while(1) {
  digitalWrite(outPin1, LOW);
  delayMicroseconds(2);
  digitalWrite(outPin1, HIGH);
  delayMicroseconds(2);
}

I've already tried to use an own delay-function, but it doesn't help.
I always have the jitter in the signal, when I look at it on the oscillocope.

3

For a digital signal: use PWM.
For analog: did you find a controller with DMA for DAC?

4

I don't know but the write statements and the looping take some time and it's probably too much time relative to 2 microseconds. ...If it doesn't come-out even and you get errors and jitter.

If there's a way to timer-interrupt every Xus that might work better.

And to be "exact" the generated frequency usually has to divide the clock frequency evenly. (I've forgotten my math... a "factor"?)

7

have a look at direct-digital-synthesis
years ago I used a pair of DDS modules to generate a pair of 1MHz sine waves with a preise phase difference for a medical experiemnt
have a look at Arduino-Controlled-AD9833-Function-Generator
e.g. 100KHz sine wave
image
you can select sine, square or triangle

10

60KHz square wave generated using a Nano with a AD9833 function generator
image

11

Thanks for the many answers.
Unfortunately, there is no suitable solution among them.

Solution with interrupts: Doesn't solve the jitter-problem.
Solution with PWM: Would work, but only for one signal. I need 2 digital signals synchronized. But the PWM outputs are independend from each other.
AD9833 has the same problem: Only one output.

This are the 2 signals I need (without jitter):
ESP32-Signal_a
The frequency and duty cycle of the two signals are the same, but they must be just as out of phase.

12

What the phase difference you need (exact value)?
Is this phase difference have to be constant or should be varied?

You need two PWM timers, chained together. It definitely could be achieved on STM32, I don't know about other MCUs.

13

have a look at the AD985X
and How to connect multiple AD985X devices
and Synchronizing Multiple AD9850/AD9851 DDS-Based Synthesizers

14

using a FY6800 2-Channel DDS Arbitrary Waveform Signal Generator to generate two 60KHz square waves phase difference 60degrees
image

using suitable DDS modules it should be possible to replicate this functionality on the ESP32?

15

Did you know that when using ledc, the ESP32 has 8-pairs of pwm channels that are inherently synchronized?

Its simple to setup (this uses channel pair 0, 1) by default ...

image
image847×136 3.8 KB

Reference

16

Thank you for all your help. I found the solution with PWM. Here is my working code:

const int output1 = 12; 
const int output2 = 4; 

// setting PWM properties
const int freq = 60000;
const int OutChannel1 = 0;
const int OutChannel2 = 8;
const int resolution = 8;
const int dutyCycle = 30;
int d;

void setup(){
  // configure PWM functionalitites
  d = 1/freq * 1000000;
  d = d - d * dutyCycle/255 /2;
  ledcSetup(OutChannel1, freq, resolution);
  delayMicroseconds(d);
  ledcSetup(OutChannel2, freq, resolution);
  
  // attach the channel to the GPIO to be controlled
  ledcAttachPin(output1, OutChannel1);
  ledcAttachPin(output2, OutChannel2);

  ledcWrite(OutChannel1, dutyCycle);
  ledcWrite(OutChannel2, dutyCycle);
}
 
void loop(){
    delay(20);
}

This is the output of the 2 signals:

output
output800×480 19.4 KB

I have used ESP32 for this. (FireBeetle ESP32-E)

17

Hi,
What is the application?

Thanks.. Tom... :grinning: :+1: :coffee: :australia:

18

I see you're using the same timer, which is good (maybe). Can't simulate on Wokwi because of an issue with the simulator.

I strongly suggest using a channel pair ch 0,1...2,3...4,5...6,7...8,9...10,11...12,13...14,15 to ensure
Jitter is within 150ns. If you inadvertently choose a channel that's on another timer, then the jitter will be up to several orders of magnitude worse!

For improved performance, use:

const int OutChannel1 = 0;
const int OutChannel2 = 1;

instead of:

const int OutChannel1 = 0;
const int OutChannel2 = 8;

Could also get better than only 8-bit resolution if needed.

20

Yes, sorry. I thought when I can make a signal without jitter I can make every signal.
But I have learned a lot from your answers and other readers will also learn how to make such signals, when they read the answers.

21

Hi [dlloyd], first I have tried with channel 0 and 1. But it doesn't work. I always get the exact same signal on both pins. That's why I used channel 0 and channel 8.

22

Hi TomGeorge, it if for testing of transformers: I use the signal as input to a H-bridge to switch the polarity in a coil of a transformer.

23

Yes, without installing the library, it won't work.

24

I have now installed your library Version 4.3.4.
When I compile your script I get this error-message:

..\Documents\Arduino\libraries\ESP32_ESP32S2_AnalogWrite\src\pwmWrite.cpp: In member function 'void Pwm::tone(uint8_t, uint32_t, uint16_t, uint16_t)':
..\Documents\Arduino\libraries\ESP32_ESP32S2_AnalogWrite\src\pwmWrite.cpp:85:62: error: 'ledcChangeFrequency' was not declared in this scope
         ledcChangeFrequency(ch, frequency, mem[ch].resolution);
                                                              ^
..\Documents\Arduino\libraries\ESP32_ESP32S2_AnalogWrite\src\pwmWrite.cpp: In member function 'void Pwm::ledc_attach_with_invert(uint8_t, uint8_t)':
..\Documents\Arduino\libraries\ESP32_ESP32S2_AnalogWrite\src\pwmWrite.cpp:308:3: error: 'ledc_channel_config_t' has no non-static data member named 'flags'
   };
   ^

exit status 1

Compilation error: exit status 1
25

You're using a version of Arduino Core for ESP32 that's too old. Its now at v2.0.9

26

Why would there be increased jitter if the second channel is on a different timer?
Aren't they all synchronous with the same clock?

Solution with PWM: Would work, but only for one signal. I need 2 digital signals synchronized. But the PWM outputs are independend from each other.

Similarly, while the PWM outputs are controlled by timers that all operate from the same clock as well. They're less "independent" than you might think! You might have to adjust some initial values to account for the setup time, but after that the outputs should pretty much stay synchronized...