The Hardware Level: Tales of hardware development from a software developer’s perspective

This past year I had the fantastic opportunity of getting to work with designing, developing, and integrating embedded hardware into a (soon to be viable) product. Prior to this I had absolutely no background knowledge in hardware engineering apart from the basic concepts of circuits from Physics in high school. I come from a software background so this was very new and exciting to me. I’m sure more experienced people will have much better advice but here are something I have learned from my stint at developing embedded hardware.

 

Open Source reference designs are your best friend when getting started

Without Arduino and Adafruit the project I am working on would honestly not be possible. The simple and approachable nature of many of their products is what helped me really hit the ground running. I designed our Bluetooth functionality around the Adafruit Feather nRF52 and other controllers around the Arduino MEGA2560 and UNO. The software development environment used to program these little things, the Arduino IDE, is so easy to use along with the C based programming language that saves a lot of time for implementing most functionality. Once we had working prototypes made in house via a slew of jumper cables, cut out project boxes, and lots of electrical tape and super glue, we proceeded to approach a PCB design firm to help us take this mess of wires into a single PCB. Although I was able to come up with the diagram and wiring I have no idea how to properly do a schematic capture or layout a PCB so I left that to the professionals. I did however learn a lot about PCBs themselves such as how they are made, what vias and traces are and how they connect things, different mounting technologies, and more which was super interesting.

 

Debugging hardware is nothing like debugging software

With software you can pinpoint control flow or data issues via a debugger or just print statements whereas with hardware everything is about the flow of electricity and signals, neither of those things can be debugged with software. If you are interested in getting into hardware you will need a multimeter for basic debugging. I recommend buying something decent since the quality of the tools you work with matters a lot more when working with hardware (more on this later). Fluke is the go to brand for quality multimeters although they are a bit pricey. There are some features that generally mark up the price of the multimeter regardless of brand, such as auto ranging which is not required but is a handy feature. Once you buy one, learn how to use it (they are pretty easy to use) and practice using it on simple circuits. Multimeters help you ensure power is going where it should with the correct amount of current at the right voltage, but what about making sure signals are ok? You can ensure that a signal is even being produced (since signals are just pulses of electricity) with a multimeter, but it’s hard to tell if you have the correct modulation and such. In these cases you will need a oscilloscope or a logic analyzer, depending on what you are trying to probe. For example, say you want to check a serial line to make sure data is being transmitted, the first step you’d do is make sure your RX and TX lines are alive with a multimeter. Once you know they have power you can use a logic analyzer or a scope to actually read the signal and even data when you use a logic analyzer. Overall, diagnosing hardware problems generally takes longer and is more involved compared to software since there are multiple things to probe with multiple pieces of testing equipment.

 

Read the datasheets for all the components you use, not just the ones that you suspect to be causing a problem

Once of the PCBs we had designed was based on the reference design of the Arduino MEGA 2560 revision 3. It’s basically the same circuitry with some our own added sensors built in in a smaller package since we don’t need jumper cable headers. You would think that since it has the same hardware it would be programmable just like the MEGA right? It’s a lot more complex than you would initially think because the MEGA comes with the microcontroller preconfigured and ready to be used with the Arduino IDE from the factory. Our PCB came with a blank Atmel ATmega 2560 as it shipped from Atmel with none of the configuration needed for it to talk to the Arduino IDE or even program via the ISP. After days of struggling, not being able to figure out why my AVRISP v2 programmer was not able to communicate with the mega 2560 I finally took a close look at the 400+ page documentation for the ATmega 2560. I found that from the factor, the mega 2560 is set to use an internal oscillator with a clock speed of 8 MHz. I needed the microcontroller to use the external 16 MHz crystal oscillator just like the reference Arduino design does. There are some fuse bits that you need to set to configure your clock signal source, but I need to get my programmer to talk the the mega 2560 before I can set the fuse bits. I then found out via manufacturer of the programmer (Pololu) that the frequency of the programmer needs to correspond with the current frequency of the microcontroller you are targeting. Since I tested my programming process out with reference Arduino hardware the programmer worked just fine because it was set to a high frequency that corresponded to a 16 MHz system clock, whereas my mega 2560 was running at 8 MHz. I lowered the frequency of the programmer and bingo I was able to communicate and set the fuse bits and got the external oscillator working. I was so sure that it was just the microcontroller the whole time I never would have guessed I need to make some changes to the way the programmer works. Moral of this story is check the documentation for all your parts, not just the one you think may be the cause of your problems.

 

When in doubt, consult the forums

There are so many great resources online for professional engineers and hobbyists in regards to hardware. If you have a problem, chances are someone else as had it too and there is a solution for it online. The Arduino forum, AVR freaks, and the hardware section of Stack Exchange have some great info. Try to search for broader solutions at first then narrow it down to the exact problem you are having.

 

I’ll try to add more points over time.

 

Published by Shravan

Computer science and general ramblings

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