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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
Are you powering the shift register and LEDs from the watch battery? Sounds possible if two LEDs on are dim?
It might be that your battery is running down! 74 series logic probably won't work that well at lower voltages.
While the watch battery is generally enough for Puck.js, as soon as you start powering external things (or executing code really frequently) you can run it down in no time at all!
To get around it, you should be able to power your shift register and LEDs from an external source of power, and connect only ground, data, latch and clock - so leaving Puck.js working off its own battery (so you don't have to worry about keeping the voltage it is powered from within range).