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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
No problem! It's pretty common as people tend to forget to mention it, and even circuit diagrams often leave out a connecting wire for it because they assume GND is always connected together :)
On most things you need GND connected. A voltage isn't really absolute - you (and the microcontrollers) need to measure it relative to something else. It's like me showing you where the top of my head is and asking you to measure my height - it's impossible unless you can also measure from where my feet are.