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Stuart Longland
f8346cdea9
The ATTiny85, as good as it is, has too few pins to really do a lot. You can buy I²C GPIO expanders, but many cost more than programming an ATTiny24A (which has more brains). The nearest equivalent is the ATTiny861, it is basically the same core as the ATTiny85, features the same PLL for high-speed PWM, but comes in a 20-pin package. They cost ~AU$3 in individual quantities. (An ATTiny85 costs AU$1.74, an ATTiny24A costs AU$1.57; thus you save about 20c and a lot of interfacing effort in going to the '861.) Thus it can interface to 8 individual switches with ease. The circuit here uses a 74374 D-latch to drive up to 8 LEDs with PWM and two 4066s to isolate the 8 inputs. Idea being, when the GPIO_EN signal is high, the 4066s are turned on and port A sees the 8 GPIO lines on the other side of the 4066s. 4066s were used because I have 4066s up the wazoo… bought a box of random ICs off eBay many years ago and it came with 5 (!) tubes of MM74HC4066s with 25 ICs each (amongst other parts, some hard-to-find). The bonus being these can be ADC inputs too if desired, allowing sensing of piezo sensors. When we want to switch which LEDs are turned on, we bring GPIO_EN low, switch port A's pins to outputs, assert the desired LEDs, then bring GPIO_EN high again. The 74374 latches those pins, and we are free to put port A back to being inputs. This happens with each sample from the synthesizer, alternating between input and output. Thus the effective rate seen on the LEDs and inputs is half the sample rate. A spare GPIO is available for turning on and off an amplifier (I use the NJR NJM2113D) to save power. The 74374's nOE pin is connected to the PWM output for the lights, thus using pull resistors, one is able to use the one PWM channel for all 8 lights. The lights are turned on in round-robin fashion, so effective duty cycle is ⅛ and the refresh rate is ~500Hz. |
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| ports | ||
| .gitignore | ||
| adsr.c | ||
| adsr.h | ||
| debug.h | ||
| gensine.py | ||
| LICENSE | ||
| Makefile | ||
| README.md | ||
| synth.h | ||
| voice.h | ||
| waveform.c | ||
| waveform.h | ||
ADSR-based Polyphonic Synthesizer
This project is intended to be a polyphonic synthesizer for use in embedded microcontrollers. It features multi-voice synthesis for multiple channels.
The synthesis is inspired from the highly regarded MOS Technologies 6581 "SID" chip, which supported up to 3 voices each producing either a square wave, triangle wave or sawtooth wave output and hardware attack/decay/sustain/release envelope generation.
This tries to achieve the same thing in software.
Code is presently a work-in-progress.