Assembled PCBs

A project log for Brushless Actuator (Arduino-Compatible)

Ardunio-Compatible M0/Zero/SAMD21 with FET Driver, MOSFETs, Absolute Magnetic Encoder, USB and RS485 comms. ~$US50

Paul GouldPaul Gould 07/05/2020 at 15:290 Comments

Ordered the boards with assembly 18th June 2020 from JLCPCB in China and they arrived in Perth Australia 29th June 2020. There is a limited range of components available, so I had to order the remaining parts, mainly the connectors and sensors, from LSCS and Mouser.

I made a mistake with the polarizing of the diodes because I didn't read the full JLC assembly notes.

I made a mistake with the choice of the SM-regulator and dual power diode. Firstly the reg requires 6V to run the 3.3V supply for the SAMD21. This is fine when running of the external power supply but when operating for the USB this is not good. I reworked the boards with LMR14206 which operates from 4.5V. Which them leads onto the dual power diode. The one I chose has a voltage drop of 1V @ 30mA which is also not good from the USB supply. So a BAT721C can be used as the replacement. It has 0.4V drop at 100mA.

The second mistake was using the DRV8305N which requires a VREG input voltage of 3.3V. I based the design on the DRV83053 which has an internal 3.3V regulator. The '3' cost twice as much at JLC than the 'N'. I just made a link between to the VREG pin from the closest 3.3V pad.

The third mistake was with the pin multiplexing limitation of the RS485 TX and RX pins. These had to be swapped over. This required lifting two pins on the RS485 transceiver chip and adding some wire links.

The fourth mistake was the spacing of the though holes of the fan/servo connector. It was designed for various pitch SMT and TH connectors but a 2.54mm 3pin servo connector wouldn't fit.