The microcontroller is the brain of the U-Build Bionic Knee. You upload your code to the microcontroller and it sends commands and receives data to the peripheral components including the motor, rotary encoder, inertial measurement sensor, and the ground contact sensor.
The microcontroller we use for the U-Build Bionic Knee is a Feather M0 Express from Adafruit. Adafruit has many resources and documentation for this device which you can find here. You will need to connect all the peripheral components to their designated pins. We use 4 pin JST PH connectors so that you can easily connect and disconnect the peripheral electronics.
The first step of the project is to wire the entire board so you can plug each system in as you go. Using connectors decreases the chance of wires breaking or ripping off the board and allows you to take components on and off the frame without having to re-solder. Follow the instructions below and reference the wiring diagram to learn how to setup each connector.
Introduction:
Construction of the main electronics board is completed in five steps. First you will add circuity to prepare the board to receive the I2C multiplexor. Second, you will connect the motor controller wires to M0 Feather Express. Third, you will build the emergency stop circuit based around an N-type MOSFET. Fourth, you will add the emergency stop connector. Fifth, you will add the PCA I2C multiplexor breakout board to communicate with different sensor units.
This project requires soldering. If this is your first time soldering, here is a link to a tutorial on how to get started. There are plenty of other resources on the basics if this doesn't answer your questions. The soldering for this project should be fairly simple and it's an easy skill to learn.
We recommend constructing the main electronics unit prior to building the leg mechanics. This way, sensors can be tested as they are installed on the leg. However, it is possible to start with preparing the shank and thigh frames, and the transmission unit prior to completing this step.
Step 1: I2C Multiplexor Wiring
This video guides you through preparing the Adafruit Feather M0 Express board to receive the I2C multiplexor. Specifically, you will route the SDA, SCL, 3.3V power, and ground pins of the Feather to the small section of protoboard on the Feather. In step 5, you will add the I2C multiplexor and make the final connections between the multiplexor and the wires added here in step 1. To complete this step, you will need small gauge wire, a soldering iron, solder, wire snips, and wire strippers. It may also be helpful to use tape or another method to stabilize the wires while you solder.
Step 2: Motor Connector
This video guides you through the process of adding the motor control wires to the Feather M0 express board. To complete this step, you will need a 4 pin pico blade receptacle, a soldering iron, solder, wire snips, and wire strippers. It may also be helpful to use tape or another method to stabilize the wires while you solder.
Step 3: E-Stop Circuit
This video guides you through the process of adding the MOSFET and E-stop circuit. This circuit combines a digital and mechanical switch such that either can disable the electric motor. In this video, we construct the digital switch component. To complete this step, you will need: the N-type MOSFET, a soldering iron, solder, wire snips, and wire strippers. It may also be helpful to use tape or another method to stabilize the wires while you solder.
Step 4: E-Stop Connector
This video guides you through the process of adding the E-stop connector. To complete this step, you will need: a 2 pin pico blade receptacle, a soldering iron, solder, wire snips, and wire strippers. It may also be helpful to use tape or another method to stabilize the wires while you solder.
Step 5: I2C Multiplexor
This video guides you through the process of adding the I2C Multiplexor. The majority of sensors used in this project transfer data over the I2C protocol. However, since some of them have the same address, we use an I2C multiplexor (PCA 9548) to route the I2C data packet to the correct sensor. To complete this step, you will need: the 8 channel PCA9548 I2C multiplexor, a soldering iron, solder, wire snips, and wire strippers. It may also be helpful to use tape or another method to stabilize the wires while you solder.
At this point, the main electronic board should be completely assembled. Move on to the next step!