jeltedirks/motor-shield-control

A Rust library for controlling DC or stepper motors with the Arduino Motor Control Shield for (2x) L293D.

Arduino Motor Shield

A Rust library for controlling DC or stepper motors with the Arduino Motor Control Shield for (2x) L293D.

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This library is written as a means to provide Rust support for the Arduino Motor Shield and operating 4 motors and 2 servos. To use this library, some schematics are provided in the schematics directory. To start off using this library, make sure that you take a look at the schematics and feel confident that you at least have some knowledge about:

• basic electronics
• bitwise operations
• rust
• shift registers

Shift Register

The shift register has its own topic in the docs files, but I will introduce it here shortly. The shift enables one to use only 3 data lines to store a full byte into memory. This is accomplished by sequentially pushying pushing data into a register, moving the bits to the next data line. Once you have the byte you want, you open a latch and the byte is stored into a memory register which will retain these values untill power is withdrawn.

DC Motors

There is great documentation to be found on the workings of DC motors, so all that is important here is that we use the L293D register to power a maximum of 4 DC motors. The data lines from the shift register are fed into the inputs of these two L293D that are present on the arduino motor shield. More on this in the docs of the motor directions and on the schematics.

L293D

Documentation about the L293D is also in abundance, so we will go over the important parts again. To make the DC motors change direction, the L293D makes use of an H bridge. It will let current flow to the DC motors in a controlled manner, and handle any counter-electromotive force that the DC motors will generate once they are stopped abruptly.

Pulse Width Modulation (PWM)

Pulse width modulation is the repeatedly setting of a data line to high and low, which gives us an easy but very fine grained way of modulating the voltage on a line without using a lot of power with variable voltage power supplies and only using binary data outputs (0V and 5V). PWM is used to give the DC motors a certain speed, and give the servo motor a certain direction it should go to.

Servo

A servo is a motor that is geared to go into a certain position once it receives a pulse width modulation setting. In order to prevent writing the entire internets documentation in this README, once again the important bits: by addressing the servo enable line with a PWM signal, the tachometer inside the servo motor will give feedback on it's current state and compare this to the received input, after which it will try to stabilize by moving the motor in a certain direction. Once it is stabilized, it will no longer try to move. This enables us to give a certain PWM signal that will always move the servo arm into a fixed position.