You are reading a single comment by @allObjects and its replies.
Click here to read the full conversation.
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.
@allObjects
As @Gordon points out, the pull-down has to be strong enough to keep noise in check. The Espruino built in pull-downs are pretty weak - only 30..40k. The limitation to 4 wires is not an issue, because the additional pull-down resistors are anyway best placed close to the watched input pins.
Since you run everything outlet powered anyway, you can have an interval triggered update of your peripherals. Having the controlling Espruino power decoupled / stabilized is good enough. Using the same (simple) decoupling technique for the shift register does not really work, because the shift register requires 4.75V minimum according to datasheet, and a regular Si diode has typically a 0.7V drop leaving only about 4.3V to the shift register. Some Ge diodes have a lesser drop - about 0.2V - but it is not a typical application. You can use a MOSFET which gives you better results (same concept as Espruino uses on the board when powered by battery: see PICO Reference, POWER, AND THE FET/B0 JUMPER).
Before going there, work on making the switching robust. The extra pull-down will for sure increase the noise resistance. You may start with just one diode and one pin and one switch and a pot in series with the current limiting fixed resistor and find optimal working point.