In the last BLDC project "Run-A-CDROM-Brushless-Motor-With-Arduino" I've used a L293 to drive a brushless DC motor. There were two important problems in that project as follow:
- Low speed and torque of the motor due to minimal signaling.
- IC overheating due to signal feedback.
In this project I solve these problems via additional L293 and corresponding hi impedance state. According to grand Wikipedia, Hi-Z (or High-Z or high impedance) refers to an output signal state in which the signal is not being driven. The signal is left open, so that another output pin (e.g. elsewhere on a bus) can drive the signal or the signal level can be determined by a passive device.
As I mentioned before, each BLDC complete turn, needs 36 steps that each 6 steps are similar as next 6 steps. So you have a sequence of 6 which repeated 6 times.
Due to having just one IC, I've used the (110, 100, 101, 001, 011, 010) signals with two states 1=high, 0=low in last project. But the correct signaling for each step is to drive two of three phases and leave the third one open (hi-z).
With three phase A, B and C:
A: 1 1 - 0 0 -
B: - 0 0 - 1 1
C: 0 - 1 1 - 0
In this table the "-" state means hi-z. So there one low and one high signal in each step. Having multiple low or high in each step will lead to wrong signal feedback and IC overheat.
Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Circuit
In this project I used the chip enable pin to make hi-z state. According to l293 schematic, there is two enable pins, each one for each side. So we can make four hi-z pins via two l293 (three of them are enough).
So this circuit is a little bit different from the last one. The pins 2, 3, 4 are enable signals and 5, 6, 7 are motor input signals. Whenever the enable pin be low, the signals will be hi-z.
Step 2: Code
As the code has written optimized, some hints maybe helpful.
- In signals array, first index is the number of hi-z pin. Remaining 3 values are signal values.
- Wait value is used to make a delay after each step.
- Serial monitor window is used to get "+" or "-" to increase or decrease wait value and it will changes the motor speed.