Wednesday, March 7, 2018

How I design an electronic product

I thought I would share the process I go through to design an electronic product.  I have been doing this type of work since the mid 1980s and while the tools and parts have changed, the process has remained much the same.  As an example I will show how I designed my own product which is a Differential Temperature Controller designed for solar heating systems.  

This device controls fluid circulation pumps that move heat from solar collectors to storage tanks.  I sell these products from my ART TEC Solar web site.

I begin by designing the schematic in CAD (Computer Aided Design).  This is the hard part that requires a lot of research to find the right components and then figure out how they interconnect.  In most products these days there is a microcontroller chip that is programmed to perform all the functions.  More on that later.  Selecting the right microcontroller begins by deciding how many things it needs to connect to or control.  These include buttons, LED indicators, LCD (Liquid Crystal) text display, and connections to external parts like pumps, sensors and power source.  The schematic drawing defines how all these parts connect to each other.
Next I design the circuit board (PCB) in CAD.  The layout software imports the signal connections from the schematic making it easier to ensure all the right connections are made.  This PCB is the physical embodiment of the schematic and involves carefully placing the parts such that the interconnections are optimized.  Key parts like the controls and screw terminals need to be placed for ergonomics and easy access.  For me, this is the fun part because it is a lot like creating an artwork and I enjoy making an aesthetically pleasing layout.
The location of every part has to adhere to electrical AND functional rules and the size of the circuit traces has to be scaled to the amount of power it has to carry.  Circuits that carry more current are wider like the green ones along the bottom in the design above. The green represents the conductive traces on the bottom side of the board, and the red are those on the top of the circuit board.  A great deal of thought goes into every minute detail to optimize size and cost.
The parts need to line up to make assembly by robot or hand easier.

Once the design is complete the file is sent to a fabricator that makes the bare circuit board.  This is a fiberglass board with plated copper traces connecting the holes where the components get inserted.  For volume production, they are tiled up into groups to facilitate machine assembly.  

Once an assembly machine has been programmed to insert all the parts, it can just copy the sequence to the rest of the boards on the panel.  For hand assembly, boards are separated and parts are inserted by hand and then hand soldered on the back.  In my design, parts are installed on both sides.

Once a prototype is assembled and tested, the next step is to write computer code for the microcontoller chip.
I write in BASIC language and have been coding in some form of that language for over 40 years.  The code defines the functions of how the device responds to inputs like buttons and sensors.  The heart of the code defines the functions of what the device does.  In this case how it responds to sensor readings and when it decides to activate a pump.  It also displays real-time temperatures on the LCD and all the interactive menu features.  The code is them compiled into machine code and downloaded into the flash memory in the chip in much the same way you save a file to a thumb drive.

Finally, I design the front panel and case.  Often for my clients projects, I work with a product designer who does 3D CAD design.  In this case, I used an off-the-shelf basic box and set up tooling to make cutouts using the woodworking equipment in my workshop.  It would have been prohibitively expensive for me to design a custom enclosure and have molds made for injection molding a low volume product like mine. 

The front panel of this product is a membrane that I designed and had fabricated.  It is flexible so that a light touch can move the membrane enough to actuate the switches behind.  It has clear windows for the LCD screen and a green LED indicator.

The final step is to assemble the whole product.  All the parts get screwed or glued together and the membrane is adhered on to the front.  Here is one that I use in the solar heating system for my workshop.

The process of developing this product took dozens of hours over several weeks.  Finally I have a product that has done relatively well in the niche market of the DIY solar heating world.  I set everything up to be scalable from making them by hand to volume contract assembly.  In boom years I contracted an assembly company to make batches of 100 pieces.  Otherwise I just build them by hand myself and it takes me about 30 minutes to assemble.  I call this my "get rich slow scheme" as orders come in almost every week. Over the years I have sold over 200 of this particular model and have two other models that have sold over 1000 pieces total. 

Many of my clients start out by ordering 1000 products for test marketing, then scale up once they have created a demand.  Most volume manufacturing is done off-shore, but for under 1000 pieces there are companies in the US that can be competitive.

If you have a great idea for an electronic product, visit my Product Design page and contact me.