# Overview TinyCandle is a simple tealight candle simulation based on the ATtiny13A. - Firmware (Github): https://github.com/wagiminator/ATtiny13-TinyCandle  # Software ## Candle Simulation The simulation code is based on the great work of [Mark Sherman](https://github.com/carangil/candle). With most LED candles, the random flickering is rather silly and lacks the spooky element of candlelight: shadows cast by the candle move because the flame is in motion. With TinyCandle, four LEDs are arranged in a square, their intensity forms a "center" of light balance that can be moved around smoothly. This 'physics-based' candlelight has the following properties: - The flame has a position and a velocity. - If the position is not centered, the velocity will accelerate towards the center in proportion to the displacement (hooke's law of springs). - The velocity has a very small damping value, which means that corrections towards the center always overshoot a bit (underdamped system). - Random "pushes" into the center position of the light are performed to mimic random drafts. - The strength of the drafts changes periodically (alternating periods of calm and windiness). ## Pseudo Random Number Generator The implementation of the candle simulation requires random numbers for a realistic flickering of the candle. However, the usual libraries for generating random numbers require a relatively large amount of memory. Fortunately, Łukasz Podkalicki has developed a [lightweight random number generator](https://blog.podkalicki.com/attiny13-pseudo-random-numbers/) based on [Galois linear feedback shift register](https://en.wikipedia.org/wiki/Linear-feedback_shift_register#Galois_LFSRs) for the ATtiny13A, which is also used here, slightly adapted. When compiled, this function only requires **86 bytes of flash**. ```c // Start state (any nonzero value will work) uint16_t rn = 0xACE1; // Pseudo random number generator uint16_t prng(uint16_t maxvalue) { rn = (rn >> 0x01) ^ (-(rn & 0x01) & 0xB400); return(rn % maxvalue); } ``` ## Compiling and Uploading Firmware ### If using the Arduino IDE - Make sure you have installed [MicroCore](https://github.com/MCUdude/MicroCore). - Go to **Tools -> Board -> MicroCore** and select **ATtiny13**. - Go to **Tools** and choose the following board options: - **Clock:** 1.2 MHz internal osc. - **BOD:** disabled - **Timing:** Micros disabled - Connect your programmer to your PC and to the ICSP header on the board. - Go to **Tools -> Programmer** and select your ISP programmer (e.g. [USBasp](https://aliexpress.com/wholesale?SearchText=usbasp)). - Go to **Tools -> Burn Bootloader** to burn the fuses. - Open the TinyCandle sketch and click **Upload**. ### If using the precompiled hex-file - Make sure you have installed [avrdude](https://learn.adafruit.com/usbtinyisp/avrdude). - Connect your programmer to your PC and to the ICSP header on the board. - Open a terminal. - Navigate to the folder with the hex-file. - Execute the following command (if necessary replace "usbasp" with the programmer you use): ``` avrdude -c usbasp -p t13 -U lfuse:w:0x2a:m -U hfuse:w:0xff:m -U flash:w:tinycandle.hex ``` ### If using the makefile (Linux/Mac) - Make sure you have installed [avr-gcc toolchain and avrdude](http://maxembedded.com/2015/06/setting-up-avr-gcc-toolchain-on-linux-and-mac-os-x/). - Connect your programmer to your PC and to the ICSP header on the board. - Open the makefile and change the programmer if you are not using usbasp. - Open a terminal. - Navigate to the folder with the makefile and the Arduino sketch. - Run "make install" to compile, burn the fuses and upload the firmware. # References, Links and Notes 1. [ATtiny13A Datasheet](http://ww1.microchip.com/downloads/en/DeviceDoc/doc8126.pdf) 2. [Candle Simulation Implementation by Mark Sherman](https://github.com/carangil/candle) 3. [Lightweight Random Number Generator by Łukasz Podkalicki](https://blog.podkalicki.com/attiny13-pseudo-random-numbers/) 4. [NeoCandle based on ATtiny25/45/85](https://github.com/wagiminator/ATtiny85-TinyCandle)   # License  This work is licensed under Creative Commons Attribution-ShareAlike 3.0 Unported License. (http://creativecommons.org/licenses/by-sa/3.0/)