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Developing Prototype Circuits from Home: Part 1, Introduction

The internet has made circuit development from home easier than ever before. This benefits engineers in a huge way by offering a venue for them to turn their ideas into physical working reality. Regardless of whether you are independent or employed by a company, there are many advantages to developing a prototype on your own.

Did you ever have that idea that your employer scuffed about however you saw the value enough to pursue it externally? Realize that you may have signed an agreement which forfeits patent rights to your employer. If you use their software or a license that they pay for or even a work computer then you may lose all rights to the patent. For employees who want to branch out with an idea, there are many software packages that allow you to capture a schematic and then transition it into a board layout and physical prototype. Unlike the days of old where you would invest thousands for design software, many website now offer free or low cost packages for developing physical circuitry.

Having recently created prototypes, I have decided to write a series of blogs that reveal the options for development as well as to guide you through the process. This first blog introduces the subject of developing prototype circuits from home. Future blogs will elaborate on the subjects introduced in this writing.

The story is told from the power circuit point of view however it is applicable to many types of circuits. Power is typically more intense from a physical aspect as well as for heat dissipation thus making layout a bit more challenging. Also, power often requires the development of custom magnetics. These complications make power a good subject for turning the virtual into the physical.

As an independent engineer or hobbyist who desires to create a working prototype, your options are not limited as much as they once were. The industry has provided flexibility in development software as well as physical prototype board development. This allows you to develop a concept into a patentable product. You can also produce working prototypes for clients who purchase your engineering skills. This process can all be completed via your keyboard over an internet connection.

Prototype development breaks down into several different sections. There is the schematic layout, board layout, and physical production.

Schematic development is well served when coupled with an evaluation software. This allows you to test run the circuit from a virtual perspective prior to spending hours building it only to discover it doesn’t’ work. Simulation software also allows you to overstress components without destroying them.

Several semiconductor manufacturers have developed online tools for schematic development and electrical evaluation. Some manufacturers such as Fairchild [5] and Texas Instruments [6] allow you to work online. Others such as LTSPICE [6] require you to download software. This is an advantage as you can continue to develop in the absence of an internet connection.

These evaluation packages hold value for the supplier as well as the customer. For the supplier, the software uses models based on its products. This encourages you to use their parts. For users, nobody knows the product better than the developer. The models are based on actual laboratory development and test data. Other options include the ability to use existing development boards or create a custom board to meet your needs. Furthering these packages is the ability to develop magnetics and board layouts complete with Gerber files. These services were outlined in reference [9].

Although readymade solutions are available through manufacturers, there are many times that a custom circuit must be made. The discussion now focuses on custom designs that require you to create your own schematic, choose your own components, and lay out your own board. In some cases you may also have to develop your own custom components such as magnetics. For this discussion, a model has to be developed for a spark gap in order to simulate an automotive ignition.

Voltage variation for timer R4 at 10%

Voltage variation for timer R4 at 10%

Voltage variation for timer R4 at 80%

Voltage variation for timer R4 at 80%

Board layout is the next phase of development. Electrical circuitry as depicted on a schematic is far different from the actual physical prototype. This is why it is important to have a connection between the electrical schematic and the physical board. National Instruments has developed a schematic layout and evaluation tool known as Multisim [7]. This package transitions easily into their board layout software Ultiboard [8]. Other board layout software packages are available from Eagle and Altium. Board software for “Fred in the Shed” home developers will be covered in more detail in a future blog.

Physical Layout of a Board

Physical Layout of a Board

Physical production of a circuit is where the rubber hits the road. Virtual simulation can only take you so far. A working prototype offers the ability to measure the circuit. This provides insight that goes beyond the limitations of physical models. Customers often desire a physical model. There are board stuffing services that save you time and money in development. If you use parts that they purchase in large quantities, you may receive a discount through them. Other services require advanced kitting of parts.

In order to create a working circuit, a physical board must be populated with components. This has created an industry of board makers and stuffers that cater to the smaller volume market. The market has gone worldwide. Prototypes can be turned in a matter of days due to electronic data transfer and overnight shipping. The process is not always a smooth one. Therefore, the discussion requires a more specific blog relating to this process.

Summary

The subject of physical prototype development involves several aspects including schematic development, board layout, and physical production. Each of these subjects has been introduced at a high level. Future blogs will go into detail on each subject. The goal is to relate the experiences of creating and receiving a prototype so that you can turn your patent into a reality or maybe just have the coolest hobby based circuit. From a personal standpoint, writing outside of my career improved my skills as an application engineer. Having a defined goal to create a prototype circuit will give you a reason to learn a new software or design technique while improving your engineering skills. It also gives you a skill to fall back on between times of employment. Who knows, it may eventually free you from cubicle life where you too can design circuits as deer prance by your window.

References

  1. PowerEsim website
  2. SMPS Power Design
  3. Ridley Engineering Power 4—5-6 software design
  4. Fairchild webdesigner website
  5. SwitcherPro(TM) Switching Power Supply Design Tool
  6. LTSpice
  7. National Instruments Multisim schematic design and evaluation tool
  8. National Instruments Ultiboard board layout tools
  9. You Need a Power Supply Designed by When?

7 comments on “Developing Prototype Circuits from Home: Part 1, Introduction

  1. MWagner_MA
    August 18, 2015

    Nice article Scott.  I'm getting back into home design and experimentation as a means of keeping my skills up.  I don't live near boston or New Hampshire, so to keep doing a decent amount of circuit design is challenging in the northeast.  I have standardized on using Eagle for schematic capture because of the tremendous support from companies like Arduino and Sparkfun for peripherals.  I then use expressPCB.com because of its ease of use and compatibility with PADS netlist (which I export from Eagle using a routine I adapted from the web).  I'm dipping my toes into 900Mhz wireless modems as a home project at the moment.

  2. Effective-Technical-Writing dot com
    August 18, 2015

    MWagner,

    Wow!  900 MHz is smoking fast for us power guys that barely get into the MHz range.  Good luck to you on that playground.  It will surely bring you challenges.

    Speaking of challenges, the software that you mention has gone to great lengths in order to assist you in your design.  Many of the problems are solved in advanced for you.  These include spacing between components (to avoid flashing over from trace to trace) and other issues such as trace width for handling currents properly.  Still, there are possible issues such as race conditions between clock and data as well as the affects from parasitics.

    As engineers we have seen our careers gain a number of extra responsibilities.  Where we once relied on support personnel for everything from arranging travel (and summarizing expenses) to laying out boards, we now assume these roles ourselves.  A recent trip to a defense contractor resulted in eight hours of time to format the expense report.  Even then it took them 7 weeks to repay even though they said it would take 4-6.  In other words, there is so much expected of an engineer that I am hoping these blogs provide valuable information that improves operating efficiency.  The expenses took eight hours, the interview lasted four.  That's how tedious this has become.  Getting back to board layout, there is a lot to know about design rules.  Eagle and Ultiboard have given us a break by applying the rules in advance.

    As we go down this road, I will be presenting the software and commenting on the user experience.  I appreciate feedback such as this as I understand that limiting the information to my experiences does not provide the value at a level a short blog allows me to.  It's a balance between providing engineers with material that is worth their time and wasting said time with too much detail.  Therefore, I encourage and welcome feedback.

    Board stuffers offer great services that can hit a snag very quickly.  Fast turnarounds are often delayed due to poor kitting and incompatible part data.  Again, we can't research and design every part so the available libraries are very helpful.  In the same manner, we rely on the accuracy of the data.  I envision that particular blog will be heavy in content about establishing a relationship and understanding the need for reliable information.  Otherwise, one could miss an important deadline for prototype delivery.  Small business owners can't afford to have that kind of situation when serving clients.  There are some very good articles on this that I will reference. 

    Please keep your comments coming as I want this subject to be a complete guide for creating accurate prototypes in the shortest amount of time.  I also want the learning curve to be quick as nobody wants to labor for hours to improve their skills after putting in a 10 hour engineering day.  My role is to improve efficiency with these blogs as it was to improve efficiency with my power designs.

    Scott

     

  3. MWagner_MA
    August 18, 2015

    I guess the lines between Power/RF/Analog gets pretty blurred these days.  I have been sucked into all the above at some point in time, but yes for power stuff, the primary concern for a breadboard is then contact resistance.  We routinely work on DC distribution on boards where we have up to 20A.

  4. Effective-Technical-Writing dot com
    August 18, 2015

    Although autorouting is a nice feature, it has a long way to go before it can match the skills of a good analog engineer.  Maybe we are more valuable than upper management?  ha ha.  Thinking that was is like trusting congress to vote on their own raises.

  5. Victor Lorenzo
    August 25, 2015

    Altium Design has a rule driven routing mechanism that provides very good results and helps a lot even during manual routing. But I still use autorouting only occasionally for some complex tasks like impedance controlled differential pairs (LVDS, USB, etc) routing, large ball count BGA fanout, tracks length matching and paralell tracks routing for buses.

  6. Victor Lorenzo
    August 25, 2015

    I agree in that “…the lines between Power/RF/Analog gets pretty blurred these day “. One of my current projects involves all of them in the same device, in the same PCB board, as part of a lightning protection system. Systems like this one have the peculiarity of being exposed to very strong magnetic/electric field variations created by the lightning strike current.

  7. Victor Lorenzo
    August 25, 2015

    The internet has made circuit development from home easier than ever before “, perhaps major role has been played by the free software and open hardware communities rather than Internet itself, but I agree in that Internet has become an invaluable tool and source of information for almost all EE today.

    I've been designing and prototyping PCBs for many years now and I find I can still learn many new things about it.

    In past years I worked for another company and we had a LPKF protomill PCB router that, once fine tuned, made great two layer PCBs. In my present occupation I make my revision A0 PCB prototypes in our workshop CNC milling machine. I started with cheap V-carve mills but results were bellow my requirements so I use now LPKF 0.15-to-0.5 cutter bits for isolation and 1.0 end mills for rubout.

    I have made PCBs with 0.2mm tracks isolation and 0.4mm hole diameter vias, but best results are at 0.25mm minimum tracks isolation, 0.3 minimum tracks width.

    Our CNC mill is one BF20LF Vario converted to CNC, using Mach3. I route the boards using Altium and flatCAM for gerber-to-GCode convertion. I evaluated a version of CooperCAM but results were disappointing. Best results can be obtained with CircuitCAM (the one I used with the LPKF machine). Many hobbiests report other add-ins for eagle and other linux based tools but most of them only support tracks isolation.

     

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