How to implement ESP8266 5 kHz PWM? - esp8266

Question

I need to realise a PWM output with 5 kHz +/- 5%. (Presumably due to a filter circuit into which this feeds over which I have no control.)
Is this realisable with a ESP8266 (ideally with NodeMCU)?
I realise that the software PWM of the ESP8266 has a maximum frequency of 1 kHz while the sigma-delta can be used to implement a PWM with a fixed frequency of about 300 kHz.
So is there a reliable way to achieve 5 kHz? I know some people experimented with the I2S peripheral for waveform output but I am unsure whether it can be used for 5kHz output.
Has anybody looked at into a similar problem before?

Answer 1

The essential code is:
#define qap 2 // Quick As Possible ... Duty cycle only 0, 50, 100%
#define HFreq 5150
#define pPulse D2 // a NodeMCU/ESP8266 GPIO PWM pin
analogWriteRange(qap); analogWriteFreq( HFreq ); analogWrite(pPulse, 1); // start PWM
TL;DR
Just did some crude benchamrks
// had HFreq=126400 with 75 KHz pulse at 80 MHz ESP clock, every 1 sec but proof of evidence lost
nominally with 80 MHz clock got
// 72.24 KHz 361178 2015061929
// 72.23 KHz 361163 2415062390
// 72.23 KHz 361133 2815062824
and
// 141.52 KHz 353809 2009395076
// 141.54 KHz 353846 2409395627
// 141.52 KHz 353806 2809395946
with 160 MHz clock
CAVEATS!!!
1. The duty cycle range is 2!
2. As well the system had no other conditioning, so other timing artifacts were still present from Serial IO etc. In particular instability due to the WDT and WiFi penultimately appeared. (Anyhow, presumably this is an issue only when the ESP8266 is under stress and duress.)
// 141.50 KHz 353754 619466806
// 141.52 KHz 353810 1019467038
// ...
// ad infinitum cum tempore finitum, infinitus est ad nauseum?
// ...
// 141.54 KHz 353857 735996888
//
// ets Jan 8 2013,rst cause:4, boot mode:(1,7)
//
//wdt reset
When using the following code to generate a 5 KHz square wave signal, the considerations above are not an issue and do not occur.
// ------------ test results for 80 MHz clock --------------
//
//
// PWM pulse test
//
// F_CPU: 80000000L
// ESP8266_CLOCK: 80000000UL
// PWM "freq.": 5150
//
//
// connect D1 to D2
//
//
// raw MPU
// frequency count cycle
// 0.00 KHz 1 407976267
// 4.74 KHz 9482 567976702
// 5.00 KHz 10007 727977137
// 5.00 KHz 10006 887977572
// 5.00 KHz 10006 1047978007
// 5.00 KHz 10007 1207978442
// 5.00 KHz 10006 1367978877
// 5.00 KHz 10006 1527979312
// 5.00 KHz 10007 1687979747
// 5.00 KHz 10006 1847980182
// 5.00 KHz 10006 2007980617
// 5.00 KHz 10007 2167981052
// 5.00 KHz 10006 2327981487
// 5.00 KHz 10006 2487981922
// 5.00 KHz 10007 2647982357 ...
//
// crude testing for 5KHz signal
// extracted from:
// highest frequency / shortest period pin pulse generate / detect test
//
// uses raw ESP8266 / NodeMCU V1.0 hardware primitive interface of Arduino IDE (no included libraries)
//
// timing dependencies: WDT, WiFi, I2S, I2C, one wire, UART, SPI, ...
//
// Arduino GPIO 16 5 4 0 2 14 12 13 15 3 1 0 1 2 3 4 5 ... 12 13 14 15 16
// NodeMCU D pin 0 1 2 3 4 5 6 7 8 9 10 3 10 4 9 2 1 ... 6 7 5 8 0
// | | | | | | | | | | |
// a WAKE | | F Tx1 | | Rx2 Tx2 Rx0 Tx0
// k (NO PWM or | | L blue | | | |
// a' interrupt) | S A * H | H | H | | * led's
// s red S D S S M S H
// * C A H C I I C
// L T L S M S
// K A K O O
// └ - - - - └----UART's----┘
// └--I2C--┘ └-----SPI------┘
//
// rules of engagement are obscure and vague for effects of argument values for the paramters of these functions:
// analogWriteRange(qap); analogWriteFreq( HFreq ); analogWrite(pPulse, 1);
//
// http://stackoverflow.com/questions/42112357/how-to-implement-esp8266-5-khz-pwm
//
// system #defines: F_CPU ESP8266_CLOCK
#define pInt D1 // HWI pin: NOT D0 ie. GPIO16 is not hardwared interrupt or PWM pin
#define pPulse D2 // PWM pulsed frequency source ... ditto D0 (note: D4 = blue LED)
#define countFor 160000000UL
#define gmv(p) #p // get macro value
#define em(p) gmv(p) // evaluate macro
#define qap 2 // minimal number of duty cycle levels (0, 50, 100% ) Quick As Possible ...
#define HFreq 5150 //((long int) F_CPU==80000000L ? 125000 : 250000) // ... to minimize time of a cycle period
// max values ^ and ^ found empirically
// had HFreq=126400 with 75 KHz pulse at 80 MHz ESP clock, every 1 sec but proof of evidence lost
#define infoTxt (String) \
"\n\n\t PWM pulse test " \
"\n F_CPU: " em(F_CPU) \
"\n ESP8266_CLOCK: " em(ESP8266_CLOCK) \
"\n PWM \"freq.\": " + HFreq + "\n" \
"\n\n connect " em(pInt) " to " em(pPulse) "\n" \
"\n\n raw MPU " \
" \n frequency count cycle "
long int oc=1, cntr=1;
unsigned long int tc=0;
void hwISR(){ cntr++; } // can count pulses if pInt <---> to pPulse
void anISR(){ tc=ESP.getCycleCount(); timer0_write( countFor + tc ); oc=cntr; cntr=1; }
void setup() { // need to still confirm duty cycle=50% (scope it or ...)
noInterrupts();
Serial.begin(115200); Serial.println(infoTxt); delay(10); // Serial.flush(); Serial.end(); // Serial timing?
analogWriteRange(qap); analogWriteFreq( HFreq ); analogWrite(pPulse, 1); // start PWM
pinMode( pInt, INPUT ); attachInterrupt(pInt, hwISR, RISING); // count pulses
timer0_isr_init(); timer0_attachInterrupt( anISR ); anISR(); //
interrupts();
}
void loop() { delay(10); if (oc==0) return;
Serial.println((String)" "+(oc/1000.0*F_CPU/countFor)+" KHz "+oc+" "+tc); oc=0; }
//

Answer 2

You can also use the hardware SPI interface which has an adjustable clock speed.
By writing continuous data, the output waveform appears on SCLK.
I've figured out the abovementioned while creating a knight rider effect with IC 74hc595 on ESP8266, using MicroPython (which is indeed slow, as being a script language).
It worked for me up to 4MHz SPI clock speed.
The disadvantage is, for permanent waveform, you need to write data to MOSI forever (as when SPI data buffer goes empty, there is no signal on SCLK anymore).