Creating Realistic Fire Effects
In various settings, whether it’s simulating an open fire in a nativity scene, replicating a forest fire in a model railway landscape, generating the warmth of a log fire in a doll’s house, or even creating the ambiance of an artificial candle, the standard steady light or the commercially available regularly flickering lights lack realism. This circuit offers a far more convincing imitation of the irregular flickering seen in real fires. To achieve this effect while maintaining flexibility and minimizing component count. A microcontroller from the Atmel ATtiny range has been chosen.
This microcontroller generates a flickering pattern, controlling two miniature light bulbs through transistors using a PWM signal. The PWM signal ensures the bulbs produce eight different light levels, creating a more natural and dynamic flickering effect. Potentiometer P1 in the RC network allows adjustment of the clock speed to the microcontroller, influencing the pace of the flickering, thus enhancing the simulation’s realism.
Intelligent Light Level Generation
Creating varied light levels through software is relatively straightforward in practice, yet the underlying theory is notably intricate, as indicated by the term ‘intelligent’ in the title. The method involves employing a digital pseudo-random number generator, specifically an 8-bit shift register with feedback organized based on the coefficients of a primitive polynomial, to generate a sequence of period 255. To avoid overly violent flickering, this sequence undergoes smoothing using a digital Finite Impulse Response (FIR) low-pass filter. This filter calculates the average of the last two sample values. For additional customization, a jumper can be added to compress the output’s dynamic range by incorporating a fixed basic intensity. The outcome is an irregular flickering pattern remarkably akin to that of a real fire.
Flexible Brightness Control
An alternative approach permits brightness values to be derived from a look-up table rather than utilizing the sequence generator. This alternative provides the utmost flexibility. A jumper allows the selection of two distinct tables. These look-up tables can be harnessed to generate diverse decorative light effects, like a light fader or the seamless blending of two differently colored lights. The concept could even be extended to replicate rotating flashing lights on a model. With an expansion to three channels, it becomes possible to connect three miniature light bulbs in red, green, and blue (or an RGB LED) and create arbitrary color patterns. The printed circuit board, measuring just the size of a postage stamp, facilitates easy integration within small models or model landscapes.
Practical Aspects and Cost-Efficiency
The board design is single-sided, devoid of Surface-Mounted Devices (SMDs), making both the fabrication and assembly relatively trouble-free. Additionally, the absence of SMDs significantly simplifies the assembly process. The overall component cost remains remarkably low, averaging around two or three pounds, excluding the circuit board expenses. Power can be sourced from any regulated 5 V supply. In instances where only an unregulated supply is accessible, it should be connected to V+. The circuit’s power consumption predominantly hinges on the chosen lamp, determining its overall efficiency.