WEEK
11: OUTPUT DEVICES
This week I decided it was time to start
getting concentrated into the development of my final project.
Quick reminder:
http://fab.cba.mit.edu/classes/863.13/people/Hasier/Week1.html
The system has three output devices: one
dc motor to move through the track and two servos for the moving head to point
the beam of the projector in any direction.
H
BRIDGE FOR DC MOTOR CONTROL
I first built Neil«s H bridge
board. The trickiest part was to remember the bottom ground pin of the h
bridge.
The board was working, but had some issues
that I was not able to completely understand:
- When I
disconnected the ISP, the board stopped working.
- When the motor
is running in the air (no rolling resistance), the h bridge works perfectly.
When the motor tries to move the car though, the h bridge still receives
signals from the microcontroller but something weird happens. The input voltage
of the board is 9 volts, and this is what the h bridge gets. But the output of
the h bridge is only 1.5volts, so the car is unable to move.
I build a second board in case there were
some issues with the traces, but I had exactly the same issues.
SERVO
MOTORS
Time to program the servos. I fabricated
Neil«s servo board. It works perfectly with Neil«s code, but it does not work
with my arduino code. My guess is that the attiny 44 does not support the servo.h
library of arduino.
Also, I found this article very useful to
understand why it is so difficult to find pure servos (not continuous servos)
that have more than 180¼ of angle control.
http://www.pololu.com/blog/24/continuous-rotation-servos-and-multi-turn-servos
BUILDING
THE HASIDUINO
Taking into account I will need a board that
controls my system, I decided to build the first version of the hasiduino: arduino + h bridge +
two servo 3 pins connectors + I/O pins.
The process was very intense, but very
exciting too. I felt self fulfilled at the end.
Sunday night: board strategy schematic. I decided
to follow the component locations of the fabduino,
and fit all the extra features in the lower part.
Monday: draw in Eagle
This process demands a lot of concentration.
The weird angled wires in the schematic are afterthoughts (when I realized I
was forgetting some connections).
Tuesday: solder components and test
First, I saved the png
at 400 dpi and the traces of the atmega 328 were too
small (left picture). Then I saved the files at 2400 dpi and it worked much
better (right picture).
Another evening in the electronics room andÉ
I burnt the bootloader
and the hasiduino works, BUT:
- I«m still
having the issue with the h bridge. It switches, but somehow only 1.5 volts get
to the car
- The servos are
powered correctly but are not responding to the program.
Homeworks for this week
I guessÉ