MLC – Projects

Getting Started

When playing Just Dance, indicators appear on the screen to tell you how well you performed a move. There are four indicators, Perfect, Good, Okay and miss – which is denoted by a red X. As part of this project I wrote a Python program using OpenCV to detect the colour and each indicator. This information is then sent via a serial port to an Arduino, which using my favourite radio modules – NRF24L01 – sends a wireless signal to the electrifying wristbands that I built.

I technically lied in my title for this project…. I am not electrocuting my friends, as this would mean death by electrifying them and as annoying as they may be I still need people to play the game with me.

Understanding The Wristbands

These wristbands are designed to deliver a controlled shock to the players when given a radio signal. They’re powered by an individual li-po cell connected to a battery management system. This then connects to the Seeeduino XIAO, which manages the radio communication through the NRF24L01 radio modules, and the shocking circuit – which is also triggered by the Seeeduino.

The shocking circuit starts by charging a 100μf capacitor to 12V. This capacitor is quickly discharged through a MOSFET into a 1:44 turn transformer, giving an output voltage of approximately 300 volts after losses.

Safety

Don’t be stupid enough to try this yourself, electrifying yourself always poses a risk. To try and minimise this whilst I was working on the project, I measured the resistance of my wrist after playing a couple games of Just Dance – As sweat would decrease this resistance – and then used an oscilloscope to record the peak voltage across an equivalent resistor set-up. Using this voltage and resistance of about 250,000 ohms I calculated the current through my wrist to be about 1.2mA – which is unlikely to cause severe damage.

Similarly, by ad mistering the shock on my wrist, I avoid the risk of damaging my brain, spine or heart – as the current only passes through a few cm on the surface of my wrist.

Finally, The Result

The shocks honestly weren’t that bad, but when I tested them on my friends their anticipation made their reactions hilarious and great for content… So I made a YouTube video!!!