RPi Homemade Hat

I have a Raspberry Pi 3B+ and I use it for simple home automation like control the TV, AC and some lights. Recently I bought a cheap Chinese CNC router and started to make simple PCBs. (I want to point that I am absolute beginner in electronics so there might be some mistakes).

One of the first idea I had was to build board for the RPi that has temperature sensor and IR LED. So this tutorial is about what tools I use to accomplish this idea.

Step 1: PCB Schematic

The schematic is very simple, the Si7020 use i2c protocol so it must be connected to pin 3 and 5 on RPi, the fan must be connected to pin 2 or 4 and all other component can be assign at different pins. Currently I use these pins because for me it was the simplest way to design the traces for the pcb.

It is important to say that when I add component(or make trace) in the pcb design I always make this component pads at least 0.6mm. For example if the pad is with size 0.6x0.4mm I make it 0.6x0.6 and this is because my CNC is unable to make it smaller without cutting too much.

Step 2: PCB Milling

For pcb milling I use 30˚ angle bit with 0.1mm tip.

FlatCamp setup

For traces cutout

• Tool Diameter: 0.13 Type V.
• The "Cut Z" should be -0.06mm.
• Enable Multi-Depth with value: 0.03
• Travel Z: 1.2
• Spindle speed: 8000(this is max for my DC motor)

For holes drill and board cutout

• Cut Z: -1.501 *I use 1.5mm F4 PCB so this value should be changed according to your pcb thickness.
• Travel Z: 1.2
• Spindle speed: 8000(this is max for my DC motor)

I left all other settings unchanged:

• Feed Rate X-Y: 80
• Feed Rate Z: 80

bCNC setup

Before start milling I run autolevel and I aways set X-Y steps for probing to be maximum 3mm.

Step 3: Soldering

For soldering I use Dremel Versatip which can be used as hot air gun or soldering iron.

First I start with the iron tip. I apply flux to every pad I will use(the brown and black sports on the pcb in image gallery are flux). After that I apply very little amount of tin. Then I switch to hot air gun, position the components on there places and start heating them.

Step 5: Run and Useful Links

For IR LED I use Lirc and for the sensor I wrote a little python script.

As you can see the temperature measured by the sensor is 31˚. The actual temp is the room was 24˚. The difference comes from the RPi temp, which is 45˚ with fan running. So when I return the measured temperature from the sensor I subtract "7˚" and the returned value is pretty accurate.

FlatCamp + bCNC tutorial

Python i2c for Si7020

Instructables for Lirc

RPi fan tutorial

If you have any questions I will happy to answer you.