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• TritiLED

  jaromir.sukuba • 08/04/2016 at 08:57 • 8 comments

  I tried to replicate #TritiLED of @Ted Yapo

  How I did it

  I suggested replacing the PIC12F508 with some newer, low-power MCU, but instead of suggesting only, I tried it for real.

  At first I tried the original code with original PIC12F508 that happened to sit nearby - to have solid ground for comparison. Then I modded it.
  

  I used PIC12LF1552, because that's what I had on hand. Instead of ceramic caps I used 10uF/16V tantallum caps, diode is BAT48, transistor 2N5401 and LED is HLMP-CE13-35CDD, because that's what I had on hand. By the way, I bought the LEDs for a particular project two or three years ago and now it's obsolete - fortunately I used different LEDs for the final version of the project. It was built on a breadboard, 5-minute quick job.

  The PIC12LF1552 is somehow different to PIC12F508, so I had to adjust the Ted's original code (by the way, missing <p12f508.inc> after #include keyword on 6th line, it assembler will throw error on original code) this way:

  ; tritiLED.asm : original version by Ted Yapo, for PIC12F508
  ; https://hackaday.io/project/11864-tritiled
  ; for PIC12LF1552 adjusted by Jaromir Sukuba
  #include    
   __CONFIG _CONFIG1, _FOSC_INTOSC & _WDTE_ON & _PWRTE_ON & _MCLRE_ON & _CP_OFF & _BOREN_OFF & _CLKOUTEN_OFF
   __CONFIG _CONFIG2, _WRT_OFF & _STVREN_ON & _BORV_LO & _LPBOR_OFF & _LVP_ON	
  	ORG     0
  	movlb	0x01		; bank 1, where interesting registers are
  	movlw	0x60
  	movwf	OSCCON		; set up to 2MHz
  	movlw	0x08
  	movwf	TRISA		; set up input-output pins
  	movwf	WDTCON		; fallthrough to WDTCON, set 16ms WDT	
          movlw	LOW LATA	; get LATA adress
  	movwf	FSR0L		; move to FSR0, use it as reference
  	movlw	HIGH LATA	; so I can avoid touching BSR again
  	movwf	FSR0H		; and high byte of address too
  	movlw	b'110110'	; GP1/2/4/5 H, GP0 L 
  	movwf	INDF0		; this is now actually LATA
  MAIN_LOOP:
  	comf	INDF0		; GP1/2/4/5 L, GP0 H -> discharge       
  ;	nop			; 
  ;	nop			; optional NOPs, wider pulse, more current
  	comf	INDF0		; GP1/2/4/5 H, GP0 L, sleeping, charging a cap
  	sleep			; sleep for 16ms
  HF_NR:
  	btfss	OSCSTAT,0	; after waking up by WDT
  	bra	HF_NR		; wait for oscillator to get ready
  	bra	MAIN_LOOP	; and do another blink
  	END

  In fact, there is not much of original code left, but the idea is still the same.

  Because PIC12LF1552 WDT doesn't allow 18ms, I set it to nearest value - 16ms.

  How it performs
  

  It works. With original Ted's circuit the 3us wide pulse and 18ms sleep time circuit draws 15uA (approximately half of the current draw measured by Ted - probably beacuse of different LED). With 2us impulse I got 11uA consumption at 3V, while light output was something I call OK-ish for night indication light. With PIC12LF1552 and 2us pulse I got approximately 1uA less current draw and the same light output.

  I breadboarded another LED next to the circuit, powered by DC current and tuned until the brigthness looked more-less the same.

  The DC powered LED has more green-ish output (higher wavelength, perhaps not very apparent on the picture) and draws only slightly more than total draw of pulsed circuit - 12,5uA versus 10,7uA. Ted's original circuit exhibited greater difference. Perhaps my LED isn't as efficient at high pulsed currents.

  I decreased power supply voltage to 1,8V and it still performed well, with acceptable light for the purpose; DC powered LED produced no visible output. Interesting it drew only 3uA at 1,8V.

  What to do now

  I'll try to get some better LEDs and will see.
  

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