riparian rap

Emriver Circuit Board Design

As our business has grown, we have improved the way our instruments are produced. In the past, we hand soldered all through-hole components to our custom circuit boards, including an Arduino. While this is okay for smaller production quantities or for product prototypes, it is not ideal for larger scale production, especially considering we produce hundreds of units per year. Hand soldering can be prone to operator error, and it is costly and time-consuming.

I’ve been focusing on transitioning our electronics to all surface-mount components and optimizing our circuit designs for turnkey assembly. This means that the same external manufacturer that prints our circuit boards for us also populates all the parts on them using machine automation. For more information about surface mount technology and assembly visit: https://en.wikipedia.org/wiki/Surface-mount_technology. While making these circuit board process changes, it is also a great time to consider changes to improve product features and operations.

Instead of attaching an entire Arduino to the board, I opted to attach the same microcontroller that it uses to the new circuit board. This allows me, and our users, to write and edit the instrument software in Arduino IDE, a feature our scientific instruments have supported for many years.

Big Muddy Control Board (Front)

Another big change was in the power management. All of our products are powered by DC desktop power adapters, some 12V, some 24V, and some 48V. This also allows our products to be operated in the field off of a universal battery. For the 12V instruments, the Arduino used to handle the power reduction to take it down to Microcontroller levels. For 24V instruments, we would add in an additional power regulator to do this. For the 48V instruments, we would connect and calibrate an external DC-DC voltage converter board. The new design uses an on-board switching mode power supply capable of handling 5-60V DC input. This means all of our instruments can run on the same board and we don’t need to add any additional chip or circuit board. Having a single power management solution that fits all cases for our instruments is important because we can benefit from economies of scale when it comes to purchasing the boards.

Our latest printed circuit board in our production instruments is the Big Muddy Control Board (BMCB). The name is an homage to our local river, the Big Muddy, and also a local legend, the Big Muddy Monster (https://www.nytimes.com/1973/11/01/archives/yetilike-monster-gives-staid-town-in-illinois-a-fright-halloween.html).

Big Muddy Control Board (Back w/ Artwork)

Feature-wise, the BMCB has a major change from the previous K500 board: The BMCB features dual microcontrollers. In our Wave Maker instrument, the PCB controls motion of the stepper motor precisely, sending hundreds of micro-steps to it per second. It also has to detect user input on the optical encoder to change parameters and start/stop the wave motion. The old design featured a single microcontroller, and changing parameters caused slight hiccups during operation due to the microcontroller being able to only do one action at a time. The new dual microcontroller design allows us to do two actions at a time and eliminates all stuttering in the Wave Maker. It also provides us with additional expandability and versatility for any new products we create that utilize this board.

Wave Maker Controller (With Big Muddy Control Board)

One factor to consider when producing a single PCB for multiple different products is the cost of components that aren’t being used, or overpaying for components that are being under-utilized in some products. Why pay for an additional microcontroller when most products don’t use it? It is a challenging decision to make when designing a board like this. To have two versions of the same PCB would require two PCB orders. Any cost savings from not including the 2nd microcontroller are negated by the loss of a bulk discount.

On a different note, I decided to not have our manufacturer populate all of the screw terminals by default on the BMCB. Certain instruments utilize different screw terminals on the board. These are used to make wire-to-board connections inside the electronics enclosure. I could have included all the screw terminals that would possibly be needed for any product, but the cost to do so was excessive. Instead, these are the only through hole components on the board, and they get hand soldered. Only the necessary ones are populated, and then they are secured using a custom jig to help hold them and make the hand soldering easier.

Another cost saving technique is to utilize PCB manufacturers’ house parts wherever possible. In our case, the manufacturer has these parts at a lower price and they always have them in stock. For our K28 controller and BMCB we use house parts like: Thick film resistors, electrolytic capacitors, diodes, and LEDs. As you can see, our new PCBs seek to improve product functionality, simplify production, improve quality and reliability, and reduce costs.