Arduino to RPi -- Galvanically Isolated I2C

Originally posted on www.letsmakerobots.com

Breakout PCB Arduino Code

I’ve waited to finish incorporating my Raspberry Pi into my bot for an ample bit. But since I know so little about electricity, I swore to myself I wouldn’t add my Pi to my bot until I was absolutely sure I wouldn’t fry it.

Well, I’m still not “absolutely” sure, but I feel this little optoisolator has brought me a lot closer. This builds on my post a week or so ago about making Eagle parts.

I plan to actually list out what tweaks a Wheezy image needs to get this optoisolator build to work. It’s actually pretty easy–but whatever you, don’t be lured in by quick2wire. Those buggers wasted most of my day :(

If anyone has questions let me know.

Oh, one note. When I populated the board I used 4.7k resistors on the Arduino side, but I pulled off everything on the Raspberry Pi side. It seems the Pi has built in pull-ups that do the job rather well.

ADUM1250ARZ Datasheet

Hope everyone is well :)

Populating and Programming and APM

Originally posted on www.letsmakerobots.com

I decided to try making an Arduino Pro Mini at home. Being done, it’s not worth it. You can buy one for a dollar more than you can make them, and it took awhile to populate. Although, it’s “fun.”

This projects was also a chance for me to test the Spying-Stalactite I built.

I’ve enjoyed it. It allows me to reflect on my strategy while populating boards. It’s simply a drop down with some high-powered LEDs (~2500 lumen), heatsink, and coolant fan. It has a hole for my iphone to do the recording. Cheap and simple. Although, I need to diffuse the light, as you might see by the video that it washes out the details of the projects. Also, I’ll add a few more lights and do away with the tungsten lamp, since the iphone is constantly in a white-balance battle as I move infront of the mixed lightsources.

I populated this board; everything came out fine (although, it was much more difficult trying not to block the camera with my head). I popped it into Atmel studio and it read out the device voltage and signature. Of course, I bricked it, as I seem to do a lot.

My next projects is a Fuse Doctor. :)

I had ordered the boards from OSHPark and had planned on making three. So, I populated another and took some time programming it. I’ve outlined my steps below:

1. Hook up the AVRISP MKII

2. Open Atmel Studio. Go to Tools – Device Programming.

3. Setup:

  • Tool: AVRISP mkII
  • Device: ATmega328P
  • Interface: ISP

Click apply

4. Read Target voltage (it should be ~5V). Read Device Signature.

  1. Open boards.txt that comes with Arduino (\Desktop\arduino-1.0.3\hardware\arduino\boards.txt).

  2. Scroll down to the area marked:

8. Pull the programming information for the board from this area. Now, I’ve bricked a few boards, but I think I’ve figured this one out. When programming this board with the MKII and Atmel Studio, you should follow this order.

1. Set the fuses:

  • Extended: 0xFD
  • High: 0xDA
  • Low: 0xFF
  • (Double check the board file to make sure I didn’t make typos)
  • Hit “Program”

2. Upload Bootloader.

“The bootloader for the 5v, 16mhz Arduino Pro Mini (which is what I built) is “ATmegaBOOT_168_atmega328.hex (Desktop\arduino-1.0.3\hardware\arduino\bootloaders\atmega\ATmegaBOOT_168_atmega328.hex).
It’s important to note that the 3.3v and 5v versions use different bootloaders.

  • Go to the Memories tab
  • Hit the browse ellipsis.
  • Select the “ATmegaBOOT_168_atmega328.hex”
  • (Double check the boards file to make sure I’m not screwing you up).
  • Hit program.

3 Set Lock Bits.

  • Go to the “Lock bits” tab.
  • Check the boards.txt file for Lockbit number
  • Lockbit: 0xCF
  • (Double check the boards.txt. I don’t take blame for bricked boards :P).
  • Hit “Program”

9 Upload the Blink Sketch; the LED by the reset button should blink.

10 Let me know how it went. If you bricked a chip using these instructions, let me know so I can modify them quick.

Now that I’m used to the camera and stalactite, I plan to annotate my next board for tips on working with 0402s.

Hope all are well.

ps. Birdmun et al., sorry bout the copyright issues. Not a professional at anything, especially video editing :)

My Eagle PCB Walkthrough

Originally posted on www.letsmakerobots.com

Addendum: Please don’t watch my videos. After Birdmun’s comment I found Hack-a-Day has created better videos (shakes fist at Hack-a-Day) and I don’t want anyone to waste anyone’s time. Although, mine has a better soundtrack and less mutton-chops :)

Hack-a-Day videos:

  1. Learning Eagle CAD Part 1 – Schematic & Custom Parts
  2. Learning Eagle CAD Part 2 – Schematic & Custom Parts (includes making a part)
  3. Learning Eagle CAD – CAM Processor
  4. Learning Eagle CAD – Layout

Original: I was speaking with TeleFox and Birdmun about finding an optoisolator for use with my Raspberry Pi; I had gotten some samples of these ICs: ADUM1250ARZ. Well, for awhile now I’ve wanted to share my dumb-luck methods for designing a board around a sampled IC.

So here it is, 20mins (sorry).

Hope everyone is well :)

Part 1 – Making the Part

Part 2 – Finishing the Part and Making the Board

Finished Eagle Files: ADUM1250ARZ Breakout Board

Mega Mini Motor Shield (M^3)

Originally posted on www.letsmakerobots.com

I finally got in my Mega Mini Motor (M3) shield that I designed. I was surprised, after populating the board: It actually worked. The board came about after making the Arduino Mega Mini. I noticed I wouldn’t really be reducing the bulk of my bot because of the amount of wiring it would take to get logic to the Arduino Motor Driver shield I was using. Therefore, I set out to design a motor driver shield that would plug right into the MegaMini. I broke out Eagle and some datasheets on an assortment of ICs.

I started out working with the L298D chip, but quickly got frustrated with the way it set on the MegaMini footprint. Plus, the flyback diodes were pissing me off. I had remembered reading that the SN754410 had internal ESD diodes. I started playing with the chip layout and got a board design I was pretty happy with.

I’ll attempt a full write up later;I’m pretty mentally fatigued from learning html/css (I know, easy. But as many know by now, cognitively, I’m as slow as a snail on salt.)

My Eagle PCB Walkthrough

Originally posted on [www.letsmakerobots.com](www.letsmakerobots.com

  1. Get over to Analog Devices and sign-up for a sample account. They seem to be pretty nice and let you order several samples every month, I believe.

2. Order a few samples of the ADXL345 chip from Analog Devices.

  1. Download the Eagle files from Sparkfun: ADXL345 (Note the price).

  1. **Sign up for an OSHPark account. **Then, upload the .brd found in the Eagle files.

  1. Order the capacitors.

2 x 0.1uF

1 x 10uF

  1. Try to learn Python while the mail peoples do their magics.

** **

  1. Flip-off your Python code and get the mail.

  2. Take everything out. ADXL breakout board, ADXL345 chip, and caps.

  3. Populate your board. At this point, a good iron will do you well. But as a general rule, start with the largest chip when soldering SMDs. In our case, it is the ADXL345. Paint some solder flux all over the exposed pads. Now, take a very fine solder, such as .022 and put some on the tip of your iron. Drag the droplet of solder across the exposed pads of where the ADXL will go. Now, after the beads have cooled, paint your solder flux over the hardened beads. The idea is to have the chip floating on this flux.

  1. Place the ADXL345 on the invisible flux, hovering over the pads. Make sure the small white dot on the the corner of the chip is in the same place the red is below.

  1. Put the board on an over turned iron. **This is the most important part: **Watch the chip. What you are hoping to see is the chip magically float in place as the solder flux flows out from under the chip, leading to the solder beads bonding with the exposed copper of the ADXL345. **Seriously, don’t look away :). **If for some reason you don’t feel the chip has bonded at each pad, then very lightly press down in the middle of the chip. I said lightly!

12. Cap that B. Erm, populate the capacitors.

** **

** **

13. Plug and pray.

14. Realize it doesn’t work because you suck at life.

15. Pull the ADXL back off, clean the pads with solder wick, and try again.

16. Repeat step 11, but this time, watch the chip, no seriously.

**17. Hook it up and check it out. **The chip is both SPI/I2C ready, but I prefer I2C. So, hook that sucker up to the Arduino and see if it works. This fellow provided code and instructions on connecting are in the code’s comments at the top.

Arduino Code for ADXL345 I2C

18. Watch as your one dollar(ish) ADXL345 does witchery.

19. Ponder the ethics of sampling chips, borrowing board layouts from SparkFun, and buying underpriced capacitors from China; all leading to saving you around $12~25–or have a beer.

20. Try not to abuse the sampling previlige.

If you have any questions, I’ll do my ignorant best.