Led Light by Gerhard Schmidt

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21772947 06 Dec 2025 14:28

Over 10 years ago Gerhard Schmidt DG4FAC on avr asm tutorial.net (site already not exists) presented such a circuit LED effect based on ATtiny13

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; ; *********************************** ; * Ledlight with an ATtiny13 * ; * (C)2012 by avr-asm-tutorial.net * ; *********************************** ; .nolist .include "tn13def.inc" .list ; ; ******************* ; H A R D W A R E ; ******************* ; ; ____________ ; / | ; RES o--| |--o VCC ; | AT | ; S3 o--| |--o S2/SCK ; | tiny | ; S4 o--| |--o OUT/MISO ; | 13 | ; GND o--| |--o S1/MOSI ; |_____________| ; ; Input port bits .equ bS1In = 0 .equ bS2In = 2 .equ bS3In = 3 .equ bS4In = 4 ; ; Output port bit .equ bOut = 1 ; ; ******************************* ; H O W T H I N G S W O R K ; ******************************* ; ; Processor: ; Operates with 1.2 Mcs/s clock ; Default R/C oscillator dived by 8 ; Default fuse settings ; Timer 0: ; Operates as fast PWM with TOP=15 ; System clock prescaled by 256 ; f(PWM) = 293 c/s ; OC0B controls PWM ratio (0 .. 15) ; OCR0B set by lower nibble of control byte ; sets OC0B output on restart, ; clears output on compare match ; OC0A sets TOP and interrupts ; Timing of cycles: ; Upper nibble of control byte sets number ; of PWM cycles (16 to 256) ; Results in times between 0.055 and 0.88 seconds ; Input switches: ; S1: if set dims down LED by half current (PWM / 2) ; S2: accelerates speed by 16 (cycle duration / 16) ; S3, S4: selects program ; 00: LEDs on and off seven times ; 01: linear up and down of LEDs ; 02: sinewave-type LEDs ; 03: anything from 00 to 03 in sequence ; ; ********************* ; R E G I S T E R S ; ********************* ; ; Free: R0..R14 .def rSreg = R15 ; for saving and restoring SREG .def rmp = R16 ; multipurpose outside ints .def rimp = R17 ; multipurpose inside ints .def rCnt = R18 ; count register for PWM cycles .def rC3 = R19 ; counter for cycles in all-mode ; Free: R20 .. R29 ; Used: ZH:ZL as Pointer to table in flash ; ; ******************************************* ; R E S E T A N D I N T - V E C T O R S ; ******************************************* ; rjmp main ; Reset vector reti ; INT0 reti ; PCINT0 rjmp Tc0Int ; TIM0_OVF reti ; EE_RDY reti ; ANA_COMP reti ; TIM0_COMPA reti ; TIM0_COMPB reti ; WDT reti ; ADC ; ; Interrupt vector TIM0_OVF ; Tc0Int: in rSreg, SREG ; save SREG dec rCnt ; next PWM cycle brne Tc0IntRet ; if not zero, continue lpm rCnt, Z+ ; read from table in flash mov rimp, rCnt ; copy byte to rimp andi rimp, 0x0F ; mask upper nibble sbis PINB, bS1In ; half intensity? lsr rimp ; half PWM cycle out OCR0B, rimp ; write to PWM compare andi rCnt, 0xF0 ; mask lower nibble sbis PINB, bS2In ; double speed? swap rCnt ; 16 times faster Tc0Int1: lpm rimp, Z ; read next table value tst rimp ; zero? brne Tc0IntRet ; not zero out SREG, rSreg ; restore SREG set ; set T-flag reti ; return from int Tc0IntRet: out SREG, rSreg ; restore SREG reti ; return from int ; ; ************************************* ; M A I N P R O G R A M S T A R T ; ************************************* ; Main: ; Init stack ldi rmp, LOW(RAMEND) ; RAMEND to SPL out SPL, rmp ; Init ports ldi rmp, 1<<bOut ; Output port as output out DDRB, rmp ldi rmp, 0x1F-(1<<bOut) ; Switches pull-up, LEDs on out PORTB, rmp ; init Z-Pointer ldi ZH, HIGH(2*Tab1) ; Point Z to Tab1 ldi ZL, LOW (2*Tab1) ldi rCnt, 1 ; counter stage 1 ; init Timer 0, Fast PWM, COMPB as positive PWM ldi rmp, 0x0F ; Compare A sets TOP out OCR0A, rmp ldi rmp, 0x00 ; Compare B to LED off out OCR0B, rmp ldi rmp, (1<<COM0B1)|(1<<WGM01)|(1<<WGM00) ; Fast PWM out TCCR0A, rmp ldi rmp, (1<<WGM02)|(1<<CS02); Presc=256 out TCCR0B, rmp ldi rmp, 1<<TOIE0 ; int on TOP out TIMSK0, rmp ; init sleep and interrupts ldi rmp, 1<<SE ; enable sleep mode idle out MCUCR, rmp sei ; enable interrupts ; ; ******************* ; M A I N L O O P ; ******************* ; Loop: sleep ; go to sleep nop brtc Loop ; nothing to do, go to sleep again clt ; clear flag in rmp, PINB ; read switches andi rmp, 0x18 ; mask all switches other than S3+S4 brne Loop2 ; program is 4 inc rC3 inc rC3 cpi rC3, 7 ; beyound limit brcs Loop1 clr rC3 Loop1: ldi ZH, HIGH(2*TabPtr) ; point to pointer table ldi ZL, LOW (2*TabPtr) add ZL, rC3 ; add displacement ldi rmp, 0 ; MSB correct? adc ZH, rmp lpm rmp, Z+ ; Read table address lpm ZH, Z mov ZL, rmp rjmp Loop Loop2: ; read switches lsr rmp ; divide by 2 lsr rmp ; divide by 4 ldi ZH, HIGH(2*TabPtr) ; pointer to pointer table ldi ZL, LOW (2*TabPtr) add ZL, rmp ; add displacement ldi rmp, 0 ; MSB correct? adc ZH, rmp lpm rmp, Z+ lpm ZH, Z mov ZL, rmp rjmp Loop ; ; Table pointers ; TabPtr: .dw 2*Tab1 ; program 4, start with program 1 .dw 2*Tab3 ; dto., program 3 .dw 2*Tab2 ; dto., program 2 .dw 2*Tab1 ; point to table of program 1 ; ; Tables for programs ; Tab1: .dw 0xFFF0 ; off and on .dw 0xFFF0 .dw 0xFFF0 .dw 0xFFF0 .dw 0xFFF0 .dw 0xFFF0 .dw 0xFFF0 .dw 0xFFF0 .dw 0xFFF0 .dw 0x0000 ; end Tab2: ; Modulated Up/Down .dw 0xA0C1 .dw 0xA1C2 .dw 0xA2C3 .dw 0xA3C4 .dw 0xA4C5 .dw 0xA5C6 .dw 0xA6C7 .dw 0xA7C8 .dw 0xA8C9 .dw 0xA9CA .dw 0xAACB .dw 0xABCC .dw 0xACCD .dw 0xADCE .dw 0xAECF .dw 0xAFCE .dw 0xAECD .dw 0xADCC .dw 0xACCB .dw 0xABCA .dw 0xAAC9 .dw 0xA9C8 .dw 0xA8C7 .dw 0xA7C6 .dw 0xA6C5 .dw 0xA5C4 .dw 0xA4C3 .dw 0xA3C2 .dw 0xA2C1 .dw 0xA1C0 .dw 0xA0C1 .dw 0xA1C2 .dw 0xA2C3 .dw 0xA3C4 .dw 0xA4C5 .dw 0xA5C6 .dw 0xA6C7 .dw 0xA7C8 .dw 0xA8C9 .dw 0xA9CA .dw 0xAACB .dw 0xABCC .dw 0xACCD .dw 0xADCE .dw 0xAECF .dw 0xAFCE .dw 0xAECD .dw 0xADCC .dw 0xACCB .dw 0xABCA .dw 0xAAC9 .dw 0xA9C8 .dw 0xA8C7 .dw 0xA7C6 .dw 0xA6C5 .dw 0xA5C4 .dw 0xA4C3 .dw 0xA3C2 .dw 0xA2C1 .dw 0xA1C0 .dw 0x0000 Tab3: .dw 0xC1C0 ; linear up/down .dw 0xC3C2 .dw 0xC5C4 .dw 0xC7C6 .dw 0xC9C8 .dw 0xCBCA .dw 0xCDCC .dw 0xCFCE .dw 0xCDCE .dw 0xCBCC .dw 0xC9CA .dw 0xC7C8 .dw 0xC5C6 .dw 0xC3C4 .dw 0xC1C2 .dw 0xC1C0 ; restart .dw 0xC3C2 .dw 0xC5C4 .dw 0xC7C6 .dw 0xC9C8 .dw 0xCBCA .dw 0xCDCC .dw 0xCFCE .dw 0xCDCE .dw 0xCBCC .dw 0xC9CA .dw 0xC7C8 .dw 0xC5C6 .dw 0xC3C4 .dw 0xC1C2 .dw 0x00C0 TabEnd: ; ; End of source code ; .db "(C)2012 by Gerhard Schmidt",0x00,0x00 .db "C(2)10 2ybG reahdrS hcimtd",0x00,0x00

😊 Taking inspiration from it I made my version from a universal board (my DIY) with attiny13 , a traistor on a spider and a star with diodes 🛠️

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

🎥

🎅 Btw It's a shame the sites are disappearing from the net Recently also disappeared khoam 👀 I hope it has a chance to come back to us yet 😇

Cool? Ranking DIY

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_ACeK_ _ACeK_

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_ACeK_ wrote 129 posts with rating 121, helped 3 times. Been with us since 2024 year.

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#2 21773292 06 Dec 2025 21:06

Urgon Urgon

Level 38

» | Helpful post? (+2)

Post #2
21773292 06 Dec 2025 21:06

AVE...

I used to do such things in C, in a few lines of code. Generally the assembler is ok, if you need to count every clock cycle. But in general you should write in C, for example. High-level languages are easier to port between platforms - in the case of microcontrollers, this is usually limited to renaming registers and sometimes changing the values in those registers. Compilers are now so good that code from C to machine code is efficiently converted. If one wants, one can set the compiler to also generate intermediate ASM source code to see how efficiently the compiler compiles....

Many old, defunct pages are available via Archive.org. I there a few years ago found a lost page about joule thieves, which hasn't existed for over a decade, and saved it to a PDF for myself....

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#3 21773564 07 Dec 2025 10:14

gulson gulson

System Administrator

» | Helpful post? (+1)

Post #3
21773564 07 Dec 2025 10:14

Beautiful times, beautiful code written by a human in assembler and not generated. Thanks for sharing a forgotten solution. May it last forever.

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#4 21773896 07 Dec 2025 15:42

robgold robgold

Level 22

» | Helpful post? (0)

Post #4
21773896 07 Dec 2025 15:42

@Urgon let me disagree with you. Nowadays, time-critical things are also generated in ASM for a given CPU and this is not a problem. I'm not talking about low-volume projects, but where every cent counts and you can't always use a more powerful CPU. At university we wrote almost everything in ASM on a '51 and it worked. Such were the times, I also preferred to write in C in AVR Studio or MPLAB rather than the bloody Platforimio or Arduino, but such were the times.

@gulson today I think it's getting harder and harder with so much code not to use AI. Especially as with the free ones you need to know what they generate for you anyway, how it works otherwise you get a mass of nonsense. Of course you can say a firm "no" but it's like trying to spell reality that you won't use a smartphone.

#5 21773929 07 Dec 2025 16:10

Urgon Urgon

Level 38

» | Helpful post? (0)

Post #5
21773929 07 Dec 2025 16:10

AVE...

Well, but nowadays in college you rather learn ARM programming in C++, not '51 in ASM. As I wrote earlier, ASM is good where you need to count every clock cycle. I generally program in C myself, but once or twice I've had to have an ASM insert because a precise sequence of instructions is required to edit the program memory. Generally, however, apart from this particular case, I have not had a situation where assembler programming was needed. And deliberately I usually reach for smaller microcontrollers, like the PIC10F322....

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Led Light by Gerhard Schmidt

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FAQ

TL;DR: ATtiny13 ASM LED effect with 293 Hz PWM; “LED effect based on ATtiny13.” Built from a 2012 tutorial, revived with code, HEX, and video. [Elektroda, ACeK, post #21772947]

Why it matters: This FAQ helps hobbyists quickly rebuild, tweak, or port the classic Gerhard Schmidt LED effect using modern tools.

Quick Facts

- MCU/clock: ATtiny13 on default RC oscillator/8 ≈ 1.2 MHz; Timer0 Fast PWM, TOP=15. [Elektroda, _ACeK_, post #21772947] - PWM rate: prescaler 256 gives fPWM ≈ 293 cycles/s for smooth dimming. [Elektroda, _ACeK_, post #21772947] - Inputs: S1 halves intensity; S2 speeds timing ×16; S3–S4 select program. [Elektroda, _ACeK_, post #21772947] - Modes: 00 on/off x7, 01 linear ramp, 02 sine‑like, 03 cycles all. [Elektroda, _ACeK_, post #21772947] - Shared pin roles: PB1=OC0B LED output; PB0=S1, PB2=S2/SCK, PB3=S3, PB4=S4. [Elektroda, _ACeK_, post #21772947]

What is the Gerhard Schmidt LED light project?

A compact ATtiny13 assembly program creates multiple LED effects using Timer0 Fast PWM and a lookup table in flash. The thread revives the 2012 design with source comments, a ready-to-flash HEX, build photos, and a demo video. [Elektroda, ACeK, post #21772947]

Which ATtiny13 pins do I connect for switches and LED output?

Use PB1 (OC0B) for the LED or LED driver. Map switches to PB0 (S1), PB2/SCK (S2), PB3 (S3), and PB4 (S4). VCC, GND, and RESET wire per the ATtiny13 standard. The code defines these bits and enables pull‑ups for the inputs. [Elektroda, ACeK, post #21772947]

How do I change brightness and speed during runtime?

S1 halves LED current by halving the PWM duty. S2 accelerates the effect timing by 16×. S3 and S4 select the effect program.

Hold S3/S4 to pick a mode.

Tap S1 to dim by half.

Tap S2 to speed the sequence. [Elektroda, ACeK, post #21772947]

What LED patterns are included out of the box?

Four programs: 00 toggles LEDs on/off seven times, 01 ramps linearly up/down, 02 generates sine‑like fades, and 03 cycles through all modes automatically. The data tables in flash drive the sequences and end with a zero marker. [Elektroda, ACeK, post #21772947]

What PWM frequency and timing does it use?

Timer0 runs Fast PWM with TOP=15 and prescaler 256, yielding about 293 Hz PWM. The upper nibble sets cycle counts, producing steps from roughly 0.055 to 0.88 seconds per segment. This avoids flicker while keeping soft transitions. [Elektroda, ACeK, post #21772947]

Can I port this to C or other microcontrollers easily?

Yes. One author notes high‑level code ports across MCUs with minor register changes, and modern compilers generate efficient machine code. Quote: “Compilers are now so good that code from C to machine code is efficiently converted.” [Elektroda, Urgon, post #21773292]

Is assembler still useful for time‑critical or cost‑sensitive designs?

Yes. Another contributor argues ASM is still generated or hand‑tuned where every cent or cycle matters. Quote: “Nowadays, time‑critical things are also generated in ASM for a given CPU.” This perspective reflects production constraints on low‑end MCUs. [Elektroda, robgold, post #21773896]

How can I recover the original tutorial if the website is gone?

Try Archive.org’s Wayback Machine. A participant retrieved a long‑lost “joule thief” page years after it vanished and saved it to PDF. Search by the original URL or page title, then export for offline use. [Elektroda, Urgon, post #21773292]

What hardware did the builder use in this thread?

A DIY universal board with an ATtiny13, a discrete transistor on flying leads (“spider”), and a star‑shaped LED assembly. The post includes photos, a HEX file block, and a video link showing the effect. [Elektroda, ACeK, post #21772947]

What fuse/clock assumptions does the code make?

It assumes default fuses: internal RC oscillator divided by 8, giving about 1.2 MHz CPU clock. Timer0 and the ISR are configured for those defaults, so set fuses accordingly if flashing a blank chip. [Elektroda, ACeK, post #21772947]

How does the interrupt routine drive the LED effect?

The Timer0 overflow ISR decrements a cycle counter, then fetches the next table byte via Z from flash. It packs duty (low nibble) to OCR0B and timing (high nibble) to set cycle length, with zero as a table terminator to switch sequences. [Elektroda, ACeK, post #21772947]

Any edge cases or failure modes to watch for?

Programming flash sometimes requires a precise instruction sequence; one author needed small ASM inserts for self‑modifying workflows. While this project does not self‑program, mixing C and ASM may still be necessary for such tasks. [Elektroda, Urgon, post #21773929]

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