The Octet Project and Endoskeleton

By Robert L. Motl

I write and perform experimental classical music in my spare time. The eight acoustic musicians in my chamber ensemble have the ability to play at a pace, or tempo, that is independent of the other musicians in the group. Instead of a conductor's single time reference, the multiple downbeat rates are individualized and presented privately to each performer through sight and touch. This guidance comes through a custom electronic timing device I designed and called an Endoskeleton, which is a compound metronome with remote displays.

The Endoskeleton is in the upper left-hand corner of screen while the Octet Project plays.

Endoskeleton Prototype My work on the device began after graduate school in 1984. My master's thesis in music was theoretical; a 20-minute composition that couldn't be performed due to rhythmic complexity. Though finished with school, I continued working on the technology to make a performance possible. Over time it led to a modest career in machine language computer programming and during that period I struggled to get started on the necessary hardware.

Were it not for Jameco Electronics' contact information listed in the February 1986 issue of Electronic Musician magazine, I would not have known where to begin acquiring parts for my only custom digital circuit. The CMOS Cookbook, also then sold by Jameco, showed what various integrated circuits do. I was trained in IBM mainframe assembly language, so I was happy to find that making a design for my needs was similar to coding in assembler but using hardware logic circuits instead.

In the same magazine issue, Thomas Henry contributed an article, "The RS-232 Drummer," showing how to energize and send serial data to an AY-3-1015D UART to make a drum machine. Though the article didn't apply the parallel data output as I'd hoped, it did provide a starting point for my Endoskeleton.

Using the trial-and-error method of design, I eventually finished my hand-made device in 1989, and it's still used today in its original state for performances of the eight-part Octet.

The Endoskeleton is composed of:

10 AY3-1015D UARTs
1 4076 CMOS Quad D Register
2 4051 CMOS 1 of 8 Switches
2 4006 CMOS Variable length Shift Registers
2 4024 CMOS 7 Stage Binary Ripple Counters
1 4023 CMOS Triple 3 Input NAND Gate
10 4001 CMOS Quad 2 Input NOR Gates
3 4050 Hex Non-Inverting Buffer
9 4069 CMOS Hex Inverting Buffers
9 4071 CMOS Quad 2 Input OR Gates
27 4511 CMOS 7 Segment Latch and Decoders
5 4076 Tri-State Latches
27 Seven Segment LEDs
18 LEDs
12 Miscellaneous Diodes
248 Resistors
70 Capacitors
28 2N2222 Transistors
46 Various Connectors
1 1MHz Crystal
8 250Ω Coil SPST Reed Relays
8 25' Four Conductor Phone Cords with Modular Connectors
8 9 Volt Batteries
8 Mini Buzzers (replaced in 2014 with vibration motors)
8 100Ω linear potentiometers
1 Power supply (from Jameco and still working!)
1 Fan
22 Blank perforated boards
11 Housings
- Miscellaneous Wiring

Complete System in Case The parts form a switch that sends two 8-bit packets of serial data to one of eight identical numeric LED display terminals. The 16-bits are enough space to express a data route, a key bit, a three-digit decimal number, a flash of light, and a tactile or haptic pulse for the musician/performer to follow when using the terminal as a metronome. The parts list includes one spare display terminal and an "error register" diagnostic device.

Besides the physical labor of hand-wiring the electronic components together, the greatest challenge was figuring out a 16-bit protocol that would work in an 8-bit architecture. I needed to send the required 16-bits as two 8-bit packets to one display, but there was only enough data space for the route code to fit in one of the two 8-bit packets. After experimenting with flip-flop circuitry, I eventually worked out a solution using a data delay method.

Complete System in Case The transistors shown on the "tactile pulse" portion of the schematic drew too much power, so it was remedied with a reed relay/battery solution.

I sketched and photographed the design as I went along, making formal documents after the device was successfully running, correctly done or not. You can visit my website to see the musical outcome, a detailed technical narrative, software code, music scores, and more.

Robert L. Motl is an IT Risk Analyst living in Smithville, Texas and is celebrating his 30th year of professional work in the information technology field. His interests include early music and working on old cars. Robert has been a Jameco customer since 1986.