0000 0001 0000 0000

It works! Super Caps for the win...

It's 0000 0001 0000 0000, or in other words a momentous binary moment of 256 videos for this channel, and...

After around 5 years of development I'm so happy to report that one of my long term projects has been converted from the energy source of a rechargeable (NiMH) battery to a super capacitor.

It seemed unlikely at the outset of this endeavour as there were four major miracles that needed to happen.

1. How to charge a super capacitor to 3.8V from a QX5252 that is used to charging a 1.2V NiMH battery? See this video for the - partial - solution.

2. Is it possible for a super capacitor to run a micro-controller for any significant length of time? See this video for the answer.

3. How does a micro-controller with no ADC determine if there is no sunshine about? See this video for the answer.

4. And finally - putting all of these components together in a fake "candle"? Will that even work? Well, see the video linked below.

Here is the final(ish) code:

/*
  Super Capacitor Candle with Three PWM

  Pseudo-random flickering to simulate a candle. Output is
  via 3xPWM channels, variables can be changed to
  alter the simulation.

  Code includes checking to see if there is light and
  sleeping during the day while the capacitor is charging.

  Tue 27 May 2025 14:13:42 AEST

  DEVICE = PFS154
  F_CPU = 50000 Hz
  TARGET_VDD = 3.8 V
       _________
      /         |
  1--|VCC    GND|--8
  2--|PA7    PA0|--7
  3--|PA6    PA4|--6
  4--|PA5    PA3|--5
     |__________|


PAC = 0b00000000 all inputs as standard

                output           off              on          pullup
                ------           ---              --          ------
pin 2 PA7 PAC = 0b10000000, PA = 0b10000000, PA = 0b00000000, PAPH = 0b10000000
pin 3 PA6 PAC = 0b01000000, PA = 0b01000000, PA = 0b00000000, PAPH = 0b01000000
pin 4 PA5 PAC = 0b00100000, PA = 0b00100000, PA = 0b00000000, PAPH = 0b00100000
pin 5 PA3 PAC = 0b00001000, PA = 0b00001000, PA = 0b00000000, PAPH = 0b00001000
pin 6 PA4 PAC = 0b00010000, PA = 0b00010000, PA = 0b00000000, PAPH = 0b00010000
pin 7 PA0 PAC = 0b00000001, PA = 0b00000001, PA = 0b00000000, PAPH = 0b00000001

*/

// libraries needed
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>

#include "../auto_sysclock.h"
#include "../delay.h"
#include "../device.h"
#include "../easy-pdk/calibrate.h"

uint16_t myrand = 2901;  // happy birthday

// initialise variables
uint8_t slowcounter = 0;
uint8_t medcounter = 0;
uint8_t fastcounter = 0;
uint8_t slowstart = 0;
uint8_t slowend = 0;
uint8_t medstart = 0;
uint8_t medend = 0;
uint8_t faststart = 0;
uint8_t fastend = 0;
uint8_t faster = 0;

// variables for different types of flicker - change to suit!
const uint8_t percentnormal = 82;     // cutoff for normal/calm
const uint8_t percentsputter = 20;    // cutoff for sputtering/normal
uint8_t flickdelay = 40;              // initial speed of flicker
const uint8_t flickdelaysputter = 9;  // "sputtering" activity
const uint8_t flickdelaynormal = 40;  // "normal" activity
const uint8_t flickdelaycalm = 95;    // "calm" activity
uint8_t choosearray = 1;              // normal waves
uint8_t delaycounter = 50;
uint8_t delaydelay = 20;

bool sunshine = false;  // is the sun shining?

// can change these too if you want to play with the candle
uint8_t waves[9][4] = {
    {4, 6, 40, 50},      // sputter flicker waveslow
    {6, 8, 50, 80},      // sputter flicker wavemed
    {8, 10, 110, 130},   // sputter flicker wavefast
    {15, 25, 60, 100},   // normal flicker waveslow
    {10, 25, 110, 140},  // normal flicker wavemed
    {20, 25, 100, 120},  // normal flicker wavefast
    {40, 60, 100, 140},  // calm flicker waveslow
    {50, 70, 120, 160},  // calm flicker wavemed
    {70, 80, 140, 180}   // calm flicker wavefast
};

bool fastup = true;
bool slowup = true;
bool medup = true;

void mydelay(uint8_t counter) {
   for (uint8_t thiscount = 0; thiscount <= counter; thiscount++) {
      _delay_us(1);
   }
}

// my random routine that hasn't changed for years!
uint16_t gimmerand(uint16_t small, uint16_t big) {
   myrand ^= (myrand << 13);
   myrand ^= (myrand >> 9);
   myrand ^= (myrand << 7);
   if (abs(myrand) % 13 == 0) {
      myrand = myrand - 23;
   }
   if (abs(myrand) % 17 == 0) {
      myrand = myrand + 11;
   }
   return abs(myrand) % 23 * (big - small) / 23 + small;
}

void getnewslow(uint8_t whicharray) {
   slowstart = gimmerand(waves[whicharray][0], waves[whicharray][1]);
   slowend = gimmerand(waves[whicharray][2], waves[whicharray][3]);
}

void getnewmed(uint8_t whicharray) {
   medstart = gimmerand(waves[whicharray + 1][0], waves[whicharray + 1][1]);
   medend = gimmerand(waves[whicharray + 1][2], waves[whicharray + 1][3]);
}

void getnewfast(uint8_t whicharray) {
   faststart = gimmerand(waves[whicharray + 2][0], waves[whicharray + 2][1]);
   fastend = gimmerand(waves[whicharray + 2][2], waves[whicharray + 2][3]);
   faster = gimmerand(2, 6);
}

// interrupt triggered when the sun goes away, voltage of small
// capacitor is drained
void Interrupt(void) {
   __disgint();  // disable global interrupts
   INTEN = 0;    // disable all interrupts
   INTRQ = 0;
   sunshine = false;
   __engint();  // enable global interrupts
}

// compares the cap voltage with the internal voltage
bool checksolar(void) {
   uint8_t compresult = 0;          // initially a byte
   compresult = GPCC & 0b01000000;  // mask the result output
   compresult = compresult >> 6;    // shift it to the least significant bit
   sunshine = (bool)compresult;     // cast result as a boolean
   return sunshine;
}


void candlingon() {
   PAC = 0b00110001;
   PA = 0b00000000;

   // see datasheet
   PWMG1DTL = 0x00;
   PWMG1DTH = 0x00;
   PWMG1CUBL = 0xff;
   PWMG1CUBH = 0xff;
   PWMG1C = 0b10100110;
   PWMG1S = 0b00000000;

   PWMG0DTL = 0x00;
   PWMG0DTH = 0x00;
   PWMG0CUBL = 0xff;
   PWMG0CUBH = 0xff;
   PWMG0C = 0b10100110;
   PWMG0S = 0b00000000;

   PWMG2DTL = 0x00;
   PWMG2DTH = 0x00;
   PWMG2CUBL = 0xff;
   PWMG2CUBH = 0xff;
   PWMG2C = 0b10101010;
   PWMG2S = 0b00000000;

   getnewfast(choosearray);
   getnewslow(choosearray);
   getnewmed(choosearray);
   slowcounter = slowstart;
   fastcounter = faststart;
   medcounter = medstart;

   while (!sunshine) {
      // ramp up slow
      if (slowup) {
         slowcounter++;
         if (slowcounter > slowend) {  // ramp finished so switch boolean
            slowup = !slowup;
         }
      } else {
         // ramp down slow
         slowcounter--;
         if (slowcounter < slowstart) {  // ramp finished so switch boolean
            slowup = !slowup;
            getnewslow(choosearray);
         }
      }

      // ramp up med
      if (medup) {
         medcounter++;
         if (medcounter > medend) {  // ramp finished so switch boolean
            medup = !medup;
         }
      } else {

        // ramp down med
         medcounter--;
         if (medcounter < medstart) {  // ramp finished so switch boolean
            medup = !medup;
            getnewmed(choosearray);
         }
      }

      // ramp up fast
      if (fastup) {
         fastcounter = fastcounter + faster;
         if (fastcounter > fastend) {  // ramp finished so switch boolean
            fastup = !fastup;
         }
      } else {

        // ramp down fast
         fastcounter = fastcounter - faster;
         if (fastcounter < faststart) {  // ramp finished so switch boolean
            fastup = !fastup;
            getnewfast(choosearray);
         }
      }

      // delay + a re-purposed random for ramp speeds
      mydelay(flickdelay + faster);
      delaycounter = delaycounter - 1;

      if (delaycounter == 0) {
         delaycounter = gimmerand(1, 100);
         if (delaycounter > percentnormal) {  // calm
            flickdelay = flickdelaycalm;
            choosearray = 6;
            delaycounter = 100 - delaycounter;
         } else if (delaycounter > percentsputter) {  // "normal"
            flickdelay = flickdelaynormal;
            choosearray = 3;
         } else {  // sputtering
            flickdelay = flickdelaysputter;
            choosearray = 0;
         }
         sunshine = (bool)checksolar();
         delaycounter = delaycounter * delaydelay;
      }

      // finally the actual PWM output
      PWMG2DTL = slowcounter & 255;
      PWMG2DTH = slowcounter;
      PWMG0DTL = fastcounter & 255;
      PWMG0DTH = fastcounter;
      PWMG1DTL = medcounter & 255;
      PWMG1DTH = medcounter;
   }
}

// close down
void candlingoff() {
   PWMG2DTL = 0;
   PWMG2DTH = 0;
   PWMG0DTL = 0;
   PWMG0DTH = 0;
   PWMG1DTL = 0;
   PWMG1DTH = 0;
   PWMG0C = 0b00100000;
   PWMG1C = 0b00100000;
   PWMG2C = 0b00100000;
}

// here is where the uC goes to sleep
void sleepnow() {
   __disgint();                      // disable global interrupts
   MISC |= MISC_FAST_WAKEUP_ENABLE;  // fast wakeup
   PAC = 0;
   PA = 0;
   PAPH = 0xFF;
   PBDIER = 0;          // there is no port B on the -S08 package,
                        // without setting this to 0 the uC will wake unexpectedly
   INTEN = 0b00010000;  // enable comparator interrupt
   INTRQ = 0b00010000;
   __engint();   // enable global interrupts
   __stopsys();  // go to sleep
}

void main() {
   // page 66 datasheet
   GPCC = 0b10010000;
   GPCS = 0b00000011; // sensitivity is affected by bit 0-3
   _delay_ms(100);  // small settle time delay

   while (1) {
      if (!sunshine) {
         candlingon();  // it's dark, start candling action
      } else {
         candlingoff();
         sleepnow();    // it's light, go to sleep
         __reset();     // seems harsh but helps with the flickering anew
      }
   }
}

// Startup code - Setup/calibrate system clock
unsigned char _sdcc_external_startup(void) {
   /* Set the system clock note it is necessary to enable IHRC
   clock while updating clock settings or CPU will hang  */
   PDK_USE_ILRC_SYSCLOCK(); /* use ILRC 55kHz clock as sysclock */
   PDK_DISABLE_IHRC();      /* disable IHRC to save power */
   EASY_PDK_CALIBRATE_ILRC(F_CPU, TARGET_VDD_MV); // Makefile has these values
   /*
   DEVICE = PFS154
   F_CPU = 50000
   TARGET_VDD_MV = 3800
   TARGET_VDD = 3.8
   */
   return 0;  // Return 0 to inform SDCC to continue with normal initialization.
}

Apologies for the non-standard circuit diagram rendered by hand!

And here is a picture of the final product.

If you think this is awesome - like I do - please share widely as feedback on this sort of breakthrough is a really important part of the development of these ideas into future projects.