Tag Archives: PCB

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.

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Custom FC

In the past weeks I made progress on the software side. I have the node editor working again and the basic RC also.

To avoid getting bored I switched again to HW and started designing the FC PCB. It will include:

  • 2 x MPU9250 and MS5611 for redundancy and better noise filtering. One of the 9250 will use SPI and the other I2C, to have bus redundancy
  • 1 RF4463F30 transceiver.
  • 1 ADS1115 for ADC conversion
  • Several status LEDs

 

PWM will be handled by PIGPIO which works very nicely. Better than a PCA9685 that only allows 1 frequency for all the outputs.

It will have a HAT layout, without the EEPROM (still not very clear what good is it).

I already started designing it in Eagle (the free version) and will do the PCB using DirtyPCB.