WEEK 12: NETWORKING AND COMMUNICATIONS

Answers to my problems from last week:

1- The H bridge not working properly. Charles, thanks for the answer: “If you look at the A4953 datasheet at

http://www.allegromicro.com/en/Products/Motor-Driver-And-Interface-ICs/Brush-DC-Motor-Drivers/A4952-3.aspx,

notice how it has undervoltage protection at 7.9 volts. Meaning if it detects

VBB less than that voltage, it will not output anything. Because the A4953 is

an automotive grade chip, it makes sense for it to not totally tank your car

battery if, for instance, it were running something like an accessory motor.”

2- The servos not working properly. They were connected to the analog pins and they need to be connected to the digital pwm pins!

This week I did a few things:

1- Implement a Bluetooth module for my final project

I was very happy to see how straightforward this was using the atmega 328p. Using the rx and tx pins of the fabduino version I did last week, I just had to connect my laptop to the Bluetooth module and I could easily send signals through the arduino serial. The program that controls the dc motor via Bluetooth is the following:

I also downloaded a serial terminal app for my android phone and was able to control the movement from my phone:

http://www.youtube.com/watch?v=d9duS41gSfA&feature=youtu.be

2- Designing and fabricating a new Hasiduino board

Improvements:

- I created two 3 pin connectors (ground, 5 volt, control signal) that allow to directly plug the servo in. I did something similar in the older version, but there I did the mistake of using the analog pins instead of the pwm digital pins.

- I also connected the h bridge for my dc motor to the pwm digital pins, in case I need to control not only direction but also speed in the future.

- It is powered from a supply using a 5 volt regulator

As you can see in the pictures below, the design is based on Neil´s fabduino, but I added the h bridge, dc motor connector, servo connectors, regulator and headers for the pins. I´m getting decent with eagle and I managed to create a pretty small board.

Fabricate, burn the bootloader with the arduino IDE and go!

3- PLAYING WITH SERIAL BUSES

I was running out of time this week, so I tried to quickly test an RS232 bus using some existing boards I have.

The idea was to create a network communicating signals from my laptop to two boards, switching the led of each board from my laptop and having each board answer to that “led on” request by saying “Hello, I´m board number X”.

Operating one board work ok, but that´s not a network yet.

Then, I connected together the rx and tx pins of the two boards.

Receiving commands worked ok. I could control the lights of both boards from my laptop. http://www.youtube.com/watch?v=BQvaTi-tPH0&feature=youtu.be

The problem was when making the boards try to communicate to my computer through the serial. It did not work. Of course, both boards want to talk to the same bus, and the one that does not talk needs to be floating so that it does not interfere with the board trying to communicate. I read in the arduino website that the way to make a pin float is to define it as an input: PinMode(pin, INPUT). The issue is that I was not able to use that command to float the tx of the atmega328p. The arduino IDE uses pin 0 and 1 as its default serial communication, and it does not let me define if they are input or output. I was not able to make it float.

That´s when I decided to use other pins as a serial. Remember that in that case you need to use the software serial library in arduino. Unfortunately, I had issues with the software serial and I failed to make the boards respond to the call.