Tag Archives: SMD

Silkopter FC

Finally, after some DHL delivery trouble the boards arrived:

pcb

After watching a few tutorials I immediately tried soldering the most difficult part – the MPU9250 chip. Turns out – if you don’t have the right flux type it’s impossible. I managed to ruin 2 boards in the process and broken 1 chip…

broken pcb

Notice the PCB changing color next to the IMU I2C pins and the ‘dry’ look. The pin header holes are also darker than the others due to the heat.

 

2 days later my new flux came: Chip Quick SMD291 ordered from farnell. This time it went much better as I was able to solder 2 chips in 5 minutes, from the first try. The trick is that tacky solder flux doesn’t evaporate from the hot air and keeps the chip floating while the solder melts (and prevents oxidation). When the solder flows, the chip kinda snaps into place and that’s it. In my first tries I used a flux pen that dried immediately and the friction between the chip and the PCB was greater than the solder surface tension – preventing the chip from snapping into place.

So this is the board almost complete, except for the ADS1115 ADC that didn’t arrive still:

final pcb

 

The last few days I spent trying to get the RF4463 chip to respond on SPI1. I expected surprises and I got them:

  • first of all, activating SPI1 on a RPI3B results in boot times of 2 minutes due to an interrupt issue with the UART driver. Solution: disable the bluetooth and use ttyAMA0 instead of ttyS0
  • next I simply couldn’t get the chip to respond at all. 2 days I spent on this until I went back to the schematic thinking the wiring is not ok. Then I realized that the chip select is connected to CS2 which is GPIO 16 but the SPI1 overlay I used uses GPIO 18 as CS. Duh! Solved by adding dtoverlay=spi1-1cs,cs0_pin=16 in /boot/config.txt
  • that’s it – it works now 🙂

 

In the last moment I added 3 WS2812B RGB LEDs thinking that I will be able to drive them with PIGPIO. I didn’t check the datasheet closely enough to see that they need PWM impulses in the order of 0.5ns whichare way below the resolution of the library.

So today after soldering the LEDs I realized that I cannot drive them. Desperate, I turned to the schematic and saw that by sheer luck I connected the LEDs to GPIO 13 – which happens to be the hardware PWM channel 1. Yaay – exactly what this library needs.

So I downloaded the lib, configured it on DMA channel 4 and PWM channel 1 and ran it and voila! It works with <1% CPU usage:

final pcb2

 

So now I have almost all the hardware working – the dual IMUs, the Baros, the RF chip and most importantly – vital for a 2016 multirotor – the LEDs.

 

I have 6 unpopulated left to give away (for free of course, shipping covered by you) if someone is interested!

boards

 

So now – back to software. The RC is coming along nicely.

Schematic & PCB

The Silk FC schematic is finished and the PCB is 70% done.

Here are some screenshots:

 

There is a bit of wiring acrobatics with the PWM connector as I couldn’t find an eagle 6×3 header so I improvised one from 3 2×3 headers… Ugly but it works.

As soon as they are done I will put them on github.

The board is 2 layers only and has the specs from my last post.

I intend to add a footprint for a RFM22B as well as the RF4463F30 so I can choose which to use, in case one of them has issues.

The board should work in both single-imu-baro more and also in dual-imu-baro.

I got 2 MPU9250 and MS5611 from my previous Drotek 10 DOF boards with a bit of hot air.

 

I’m really curious how it will end up as this is my first SMD board and especially my first QFN package. The MPU is really really tiny – like 2 square millimeters.