(1) Understanding Neon and Power supplies

A project log for Real-Time Audio-Controlled Neon

Building a system that encodes and reads music in MIDI format and controls the flashing of a Neon Sign with minimal latency

davidgargesdavid.garges 10/07/2018 at 22:270 Comments

There is a huge demand for the ability for Neon to interact with music and sounds. The current infrastructure that supports musical interaction is a microphone that performs a Fast Fourier Transform to determine frequency components - much like an equalizer in your car. This is problematic because in order to detect a 100Hz bass drum, the interface must record the entirety of the sound (10ms) and then process it. The human ear can perceive delays of 10-20ms which means that the delay is already pushing the boundary of human perception. In addition, it is difficult to separate specific instruments such as bass drum, snare, or synthesizer because these instruments span the frequency spectrum. This is why it can be challenging to identify particular instruments visually when observing an equalizer in your car. 

As a DAWless Jammer myself, I realized that MIDI instrument signalling is a fast and unique way to trigger individual instruments. My vision is to read the trigger signals from individual drum instruments from a drum machine in order to then trigger a Neon tube on and off in sync with the sound that the listener is hearing. 

The first step in accomplishing high-voltage switching is understanding design requirements, the load (Neon gas), and how power is converted. 

At 180 BPM (upper limit of music tempos) and 4 hi-hat hits per beat (16th notes) this comes out to a constant on/off switching period of 80ms. This means that any transient or steady state latency issues have to be an order of magnitude lower than these design requirements. Latency could arise from the load or the power conversion.

I used the internet to understand Neon gas and any latency issues here: From this paper it is suggested that only a few tens of attoseconds are required for Neon Gas to glow. 

I enrolled in a class at the UC Santa Cruz Extension program to help me understand power supplies: High Efficiency Switch-mode Power Supply, Design Overview is a 10 week class that introduces the fundamental concepts of a real switch-mode power supplies and its functions, operations and interactions. Discussion cover the various topologies as they relate to power supply operation, design, component selection, and rating for a particular application. Using the resources from this class I was able to determine that Neon was based in an LLC Power Converter Topology with an input of 120Vac at 60Hz from the wall and an output of 5kVac at 25kHz. My first idea was to use a straight forward power supply with a GPIO-controlled relay.  Unfortunately, physical contact relays can only switch every 2 seconds which is far from the design requirements. Chatting with a gentleman in DigiKey, we realized that only solid state switchers would be able to toggle a voltage of this magnitude so quickly.

I contacted Neon transformer suppliers to understand any existing infrastructure that allowed : Tom at Tech22 helped me realize that I could not only take advantage of the opto-isolator that is inherent in the Neon transformers, but he also had developed a "switcher" which allows a Neon designer to make their lights flash. He claimed that these power supplies could have a turn on time of 30ms - which was perfect for my design requirements. Upon further investigation, I was able to understand that the switching interaction was strategically taking advantage of the opto-isolator in the voltage feedback control loop. The transformer and the switcher are two separate units where the power supply has been modified to allow access to the opto-isolator. The goal moving forward will be to utilize the transformer's switching input by imitating the switcher's output with an Arduino's GPIO.