# global open time

- use kicad 8, 9 still has some problems  
- have 2 leds: power & debugging  
        debugging: run a blink program and make sure your mcu is still alive.  
        how to use the pin with the led? just solder pin header before or after the led.  
- 2 layers  
        put pin through the board -> bam, 2 layers  
        you can connect then the two pins on the backside with a cable. there is no shame in that btw.   
- suggestion: use labels. makes your design a bit easier.  
- use disconnected mark in kicad if pins are not connected  
- use power flags if you get errors regarding power  
      - you need to tell kicad where power is coming into the board  
      - hit p on keyboard  
- pull-up & pull-down: check adrians doc  
        - if you do not connect the open switch directly to pin, there will be noise due to --- internal processes in the chip  
        - add pulldown resistor with low resastance so that noise rather goes to ground.  
        - how big pulldown resistors to be? (ricardo marques)  
            - for buttons you can use lke 5k,  
            - LEDs between 500 and 1k  
            - i2c depends on a few variables but between 900 and 5k.  
            - for 3.3v logic don't go over 2.5k  
- [getting started with electronics](https://archive.org/details/getting-started-in-electronics/page/n5/mode/2up) pgase 6 to 41. for this weeks assignment  
- make beautiful pcb, not a square. it is the design week  
        - check ccc talk  
- make power lines of fatter thickness on a pcb  
        - you see it better  
        - signal lines you want to be thin  
        - thick power lines can handle more current  
- some more about pullup/pulldown by ricardo marques  
        - if you dont use pulldown pullup, there a tristate. its not defined what voltage is on the pin. internals of mC.  
        - this is explained further by neil in input devices  
- only use bat gnd and bat vin if usb is not used. otherwise they will conflict.  
    (source: rico)