Sensor Board Schematic


Originally published at:


I’ve run across the confusion you had with the hidden pins before, I think with a 555 timer, this is actually done intentionally by many of the KiCad built-in parts. There is a page that describes how they are intended to be used, coincidentally uses the exact same part:


I am working now on this course and can’t see really why we need a capacitor on the latch pin of the shift register. I understand the decoupling capacitors attached to the power pins of the shift register and the temperature sensor, but the latch pin is different. Wouldn’t it slow down the signal that clocks the internal latch? Moreover, wouldn’t that require a larger initial current from the gpio pin used to drive that signal? I have also looked at the web page that Chris was referring to in the videos, and I cannot see that capacitor anymore. Can anybody help me to undertand it?


Christian Tenllado's build log

Yes, this would be the main function, as well as removing any potential small spikes that could mistakenly latch the circuit. I believe it was in there to ensure all other pins had settled before the latch happened. The latch will happen “last” even if all the signals occur at the same time.

You don’t need to populate this, but if you see errant behavior, this might be a place to check.


Thanks Chris, now I see.