6 Channel DRSSTC Show Controller

Published: July 21, 2021. Updated: July 15th, 2022.

This project is about building a Tesla coil show controller that can control up to 6 Tesla coils at once. It will all be housed in a transportable 19″ rack mount flight case for ease of transportation and to protect the electronics. It will feature individual interrupters, touch screen controlled MIDI interrupter, safety features to ensure a safe method of working with the Tesla coils before a show, under a show and after a show.

The 6 channel MIDI interrupter is the feature-rich Syntherrupter. Made by Max as he shares all the plans, documentation, code and schematics.

The normal DRSSTC interrupters with additional audio input is a free and open design made by Dan / Profdc9, you can download the schematics and gerber files to order the PCB boards for yourself.

The above layout is my initial idea of how I would place the different features, with a high focus on ergonomics for the most used parts like interrupters and a high focus on safety, so that pushing anything by accident is limited to a minimum. This is a rather big project and a lot of the detailed design is first done at each stage. I have split the project into the following 8 parts.

Part 1 – The parts
Part 2 – Programming Syntherrupter
Part 3 – 6 optical outputs build
Part 4 – Interrupters
Part 5 – Syntherrupter and MIDI
Part 6 – Audio input panel
Part 7 – Safety panel
Part 8 – Power supply

Part 1 – The parts

I bought a 19″ transportation rack, empty panels and power bar from the German company Adam Hall. A supplier to many smaller retailing companies of disco, event and show business equipment like audio, light and transportation gear. In this video I go through unpacking and unboxing of all the parts and walk through the initial layouts.

Part 2 – Programming Syntherrupter

In part 2 I go through features of the syntherrupter, firmware flashing, microcontroller / display programming and test of the Tiva development board and Nextion display. Max wrote an extensive and very good documentation on setup, programming and all features.

Having the “Intelligence” version of the Nextion display did result in some issues. For some reason Nextion decided that a more powerful version of their display should have a whole range of new properties on screen elements and not interpret a project file the same way that the basic / enhanced versions does… Some of the missing graphics was fixed by copying links to graphics to an additional configuration field called pic1, but the way nightmode is made, it was not possible to get the right graphics for that. Max has since this video was recorded released a new Nextion display software version, that will be shown in a later video. This also includes new functionality support for the “Intelligence” version of the Nextion display.

I tested the output from the Syntherrupter, through a optical output circuit and into the driver of a DRSSTC. The results are described on the individual oscilloscope screenshots, but it really shows nothing out of the ordinary. Its a good sturdy drive with good rise and fall times, only worth noting is the 3 uS delay in turn-off caused by the total delay from Syntherrupter to optical input in the driver.

Part 3 – 6 optical outputs build

The single output that was tested in part 2 is made into a complete set of 6 optical outputs in a panel with switches for selecting different interrupters, indication LEDs and dry test speakers. The panel features for each of the 6 channels:

  • Optical output transmitter IF-E96E, 1mm plastic fiber
  • Output LED indicator
  • Switch to turn on/off optical output transmitter
  • Switch to select between two different interrupters
  • Switch to turn on/off dry test speaker
  • Dry test speaker

I wanted everything on one PCB for the outputs, like switches and wires for all. Luckily I still have a lot of color-coded multi conductor cable that I cut up to use the single wires. Makes it very easy to work with large wire bundles and quickly identidy or make some identical.

Download Schematic and download PCB layout. Schematics are made in https://www.expresspcb.com/pcb-cad-software/ which is just an old habit of mine for creating real fast schematics and PCB layouts, when I etch the PCBs myself.

Part 4 – Interrupters

6 regular DRSSTC interrupters are build from the free and open designs from Dan / Profdc9 on highvoltageforum.net.

Download layout drawings. Drawings are made with the free draw.io software, which can be used both online and a downloadble dekstop application.

I built 7 interrupters, one for each channel and a master interrupter, that by a switch, can take over any channel. Each channel can also switch between normal and burst mode.

The interrupter also has a “sound” input option, which can take any kind of regular audio output and transform it into a on-time limited square-wave signal. This feature is first implemented in another part, as this panel could not fit anymore control inputs.

Using the color coded wires, it was easy to keep track of the hundreds of wires. Each interrupter repeats the individual colors I used for the output panel channels, but also for the interrupter itself it uses identical colored wires for each interrupters control inputs. This way its easy to distinguish each channel, but also rule out any faults as all channels looks identical.

Part 5 – Syntherrupter Installation And MIDI Test

In this video I mount, update and test the Syntherrupter with its MIDI capabilities and gives a walk-through on how I am using it. Some of the details from the video is written as a part of this post. To read all the parts, read the article about the complete DRSSTC controller project.

First I had to upgrade the firmware, since this was about half a year since it was first done. Max had put out 6 new releases in the meantime, which also included support for the 7″ Intelligence version of the Nextion display. So no more custom editing and changes to the display, I can just download the image to it!

MIDI Setup for Tesla Coil

The first tests after upgrading the Syntherrupter firmware from v4.1.0 to v4.2.0-beta.3, was to test the simple mode with coil settings with oscilloscope. It was confirmed to be 100% accurate with an example of 280 Hz at 60 uS on-time.

For the PC MIDI Setup, I ran through the suggested programs in the Syntherrupter documentation. https://github.com/MMMZZZZ/Syntherrupter#pc-midi-setup. The free SynthFont 1 program gave me a lot of problems with virtual COM port locking up after each played MIDI. I had to close the program and open it again. I then tried Hairless MIDI<->Serial and loopMIDI together with my regular MidiEditor program. That worked flawlessly.

To get into the coil settings, its good to remember that buttons with additional settings behind, are highlighted with a double frame in the Syntherrupter UI. You access these deep menus with a long press, as defined in ms in the overall settings menu.

The cutout for the display was not great, I have unfortunately misaligned something. So its shifted 2 mm both left and down. But overall you do not really notice it and the layout of the panel is satisfactory.

Part 6 – Analog Audio Interrupter and Test

In this video I install and test the analog audio interrupter and gives a walk-through on how I am using it. All schematics for the circuits and PCB layouts are available at the project thread: Project thread: https://highvoltageforum.net/index.php?topic=1417.0

The DRSSTC analog interrupter audio input is quite simple and build up around a single LM339 op-amp. It has a toggle switch between normal BPS interrupter output and the op-amp output. The potentiometer is a frequency bandwidth limiter setting somewhere between allowing a maximum frequency from 100 up to 500 Hz. Overall on-time is still limited by the normal potentiometer for on-time adjustment.

The amount of wires is getting out of control. I am however very happy about the color-coded wires, as its still easy to follow single wires back to its origin.

If you missed the first 5 parts of this project, check out the earlier videoes here:

Part 1: https://www.youtube.com/watch?v=Ad2129sZv6w
Part 2: https://www.youtube.com/watch?v=jQZj8DPNvJg
Part 3: https://www.youtube.com/watch?v=DCFt82_SrNI
Part 4: https://www.youtube.com/watch?v=pOEmQ9KFFWY
Part 5: https://www.youtube.com/watch?v=JB4-n_mJty4

I am building a Tesla coil show controller that can control up to 6 Tesla coils at once. It will feature individual interrupters, touch screen controlled MIDI interrupter, safety features to ensure a safe method of working with the Tesla coils before a show, under a show and after a show. It will all be housed in a transportable 19″ rack mount flight case for ease of transportation and to protect the electronics. The 6 channel MIDI interrupter is the feature rich Syntherrupter made by Max Zuidberg. He shares all the plans, documentation, code and schematics on: https://highvoltageforum.net/index.php?topic=1020.0

Part 7 – Safety Features

In this video I install and test the safety features. A lot of the original plan to have the safety relay in the show controller has changed and instead turned into a separate project, with building a soft start safety box that receives a special emergency signal from the controller.

A encoded signal (666 Hz) is sent over fiber optical link to a soft start safety box (bandpass filter from 400 to 1100 Hz) where a industrial grade safety class circuit is made to cut off mains supply to the Tesla coils in case of a malfunction in the monitored circuit or a pressed emergency stop.

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