Homebuilt Hardware

I have built a digital VCO with a dspic30f3013. It is a numerically controlled oscillator (NCO) with the exponential conversion performed in the dspic using a lookup table. The NCO phase is used to lookup a triangle waveform. The triangle wave is output through an 8bit R2R DAC. The normal VCO waveforms, sine, sawtooth, and PWM, are generated using analog circuitry. For this first version, I wanted to create a traditional VCO, but future versions may include additional waveforms.

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I have built a simple sallen-key VCF using a miniature tube (1J17B) as the main amplifier. There are a few opamps in the signal path, but they are only used with a gain of 1 as inverting and non-inverting buffers. The circuit is based on Ken Stone’s tube VCA which uses the 1J24B. The cutoff frequency is controlled using a dual vactrol.

project page

A little tutorial on Atmel AVR Development in Ubuntu with the AVRDragon and STK500. Part 1 describes  hardware setup and interface modes. It can be found here. This tutorial covers the initial setup of the AVRDragon in Ubuntu linux. Most of it is applicable in other Linux distributions. The goal is to show how to set the AVRDragon’s programming mode and connect through the USB port.

I have just purchased www.homebuilthardware.com. This site is basically live now. It is a generic name but eventually I plan to have the Synth-DIY section as a subsection of a more general electronics DIY website. It has been a while since I have completed any projects. In the next few weeks I plan to finish up some modules that are partially complete. I now have all the needed parts to set up the my second cabinet. Last week I received some MOTM bread boards which will do nicely for prototyping some designs.

Over the last few days, I have been thinking about a digital noise circuit. The CD4006 (18-bit shift register) is commonly used but it is becoming difficult to find. Instead, I have written assembly code for a 32bit Linear Feedback Shift Register (LFSR). This code is programmed in an ATTiny13 8bit AVR microcontroller. The tiny13 runs with an internal clock of 4.8MHz. I have coded two versions; the first runs in self-clocked mode with a 192KHz shift rate and the second uses an external interrupt for the shift clock and this one supports up to 145KHz shift rate (290KHz with a 9.8MHz cpu clock). These two designs offer a low parts count and small footprint noise source. I’ll be updating the project page here after I have tested these and some more ideas.