Which Synthesiser Modules Has Jet Holt Made with Frequency Central?

Jet Holt has co-designed and programmed four synthesiser modules with Frequency Central: Bartos Flur (an esoteric sequencer/trigger generator), Deep Thought (an all-in-one boolean logic module), Polygraf (a programmable drum sequencer), and Chronograf (a start/stoppable low frequency oscillator). According to his site, he works with PIC microcontrollers and writes the firmware in assembly code. The module pages link out to Frequency Central for product details, so use those links for current availability and specifications.

The Four Modules at a Glance

Bartos Flur: Esoteric Sequencer/Trigger Generator

Bartos Flur was the first synth module Holt programmed, created at age 17 for his A-level Electronics course. Its defining quirk is that the active step is set by the input voltage level rather than by a conventional clock-and-counter arrangement. Holt describes it as "weird... but fun, too." If you want a sequencer that responds to control voltage in an unusual way, this is the one to look at; if you expect a standard step sequencer, its behaviour will likely surprise you.

Deep Thought: All-In-One Boolean Logic

Deep Thought grew out of a joke: while explaining logic gates to a teacher, Holt suggested building a circuit with gates, switches, and LEDs that could serve as a learning tool. The result includes all the logic gates plus a section that can act as any gate. The name is a Hitchhiker's Guide reference, and Holt's own framing—hoping it won't take 7,500,000 years to produce answers—signals that this is a hands-on teaching and experimentation module rather than a performance tool.

Polygraf: Programmable Drum Sequencer

Polygraf began as an experiment in which Holt inadvertently built a powerful sequencer that "normal people" would struggle with, since reading binary was effectively required. Adding seven-segment displays and a reworked record mode made it usable, and Holt quotes a description of it as "like something Roland would have created in 1978." The lesson from its development: a deep sequencer needs a readable interface, and the displays and record mode are what turn the underlying engine into a playable drum machine.

Chronograf: Start/Stoppable Low Frequency Oscillator

Chronograf was designed as a controller for Polygraf and similar modules—something to tell them when to start, when to stop, and which sequences to play. Holt's favourite feature is the variety of waveforms it can produce, which makes it a flexible modulation source as well as a transport-style controller. If you already run a Polygraf-style sequencer, Chronograf is the companion module; if you need a general-purpose LFO with many shapes, its waveform range is the draw.

How the Modules Fit Together

The set splits into two rough groups. Bartos Flur and Deep Thought are exploratory and educational—one plays with voltage-controlled step selection, the other with logic gates. Polygraf and Chronograf form a performance pair: a drum sequencer plus a module that conducts it. Holt's technical approach is consistent across all four: PIC microcontrollers programmed in assembly, a choice he notes gets him called a troglodyte.

Practical Notes Before You Look Further

• Check Frequency Central for current status. Holt's pages describe these as collaborations and link to Frequency Central; the stages listed (prototype, in development) reflect the site's own labels and are not a statement about what is sold today.
• Expect documentation to matter. Polygraf's history shows that a sequencer this deep lives or dies on its interface; read the Frequency Central materials on the record mode and display behaviour before committing.
• Match the module to your goal. For learning logic, Deep Thought; for unconventional CV-driven sequencing, Bartos Flur; for drum programming, Polygraf with Chronograf as its controller.

Holt's personal site also covers his other interests—video games, running, languages, photo editing, and SVG—but the synthesiser modules above are the extent of the Frequency Central collaboration described there.