Firefly Design LLC

Product Design Consulting

Mechanical Prototyping & Low Volume Production

Posted by Denis Bohm on January 28, 2019. 0 Comments

With our new Tormach 1100M CNC Mill we can now create mechanical parts out of most materials (plastics, aluminum, steel, brass, etc).  This gives us the ability to create full prototypes and also do low volume production in house.  We have used this capability to create device enclosures, assembly fixtures, and production stations.

Case Study: Sensor Project

A recent project required a small water-proof sensor.  Low volume production was needed to conduct internal studies.  An enclosure consisting of two parts was designed.  The top part has a white feature that is used for alignment into a strap and doubles as an LED indicator.  The bottom part has a magnetic USB connector. The two parts are held together by screws and there is an o-ring in-between to make a waterproof seal.

Top Part

The top part was made by first welding white ABS sheet to black ABS block.  These are attached to a custom fixture plate so that multiple tops can be milled in a single pass.  The white is milled away from the top to leave just the alignment/indicator feature.

On the back side, the black is milled away to reveal the white indicator feature.  There are also alignment features for the internal PCBA, a grove for the o-ring, and holes for metal inserts that will securely hold screws.  A custom thermal press hot end, clamp, and adapter plates were made to ease insertion of the tiny metal inserts.

A set of completed top parts:

Bottom Part

The bottom part is milled from a large black ABS sheet.  The same custom fixture plate is used to make multiple parts in a single pass.

    To complete the bottom part, a magnetic USB connector is glued in place.

    Final Assembly

    A PCBA and battery are assembled into the top and bottom parts.  An o-ring and screws join the two halves to make a waterproof assembly.

    The fully assembled device with USB cable attached:

    Water Testing

    A water tester was used to check each prototype.  The prototype is magnetically attached to the mount inside the tester.  The tester is pressurized to 3 ATM and the device is submerged into the water.  A visual check is done to check for air steams leaking from the device.  This device was tested up to 6 ATM and passed all tests.

    Production Station

    A production station was created for the PCBA in this device.  The production station is based on a custom platform that we designed and have used for multiple clients.  The custom platform consists of a complete test station with electronics and software - all designed and built in house.  To customize the platform for a client, a unique test head is created using our software.  The test head consists of a PCB with test point probes and a mechanical component to hold the PCBA under test in place.  The software is customized by creating a test script specific to the PCBA.

    The production station attached to a computer via USB showing a successful test and programming pass:

    The custom test heads are the black parts in the image below.  The top test head contains all the test point probes in this case.  The bottom test head holds the PCBA securely in place.


    The addition of the mill rounds out our capabilities so that full devices can be made in house including mechanicals, electronics, firmware, and apps.

    Firefly Ice: Timing Demo

    Posted by Denis Bohm on October 06, 2014. 0 Comments

    The Firefly Ice has a quick simple proof of concept "timing" demo.  This works by using two Firefly Ice devices.  Each device recognizes an event.  When the event is recognized the accelerometer data is saved from right before and right after the event.  The saved data is synced from both devices to the Firefly Utility app and the timing between the two events is shown in a graph.

    Checkout the Timing Demo page for details.


    Firefly Ice: Raw Data Capture

    Posted by Denis Bohm on October 06, 2014. 0 Comments

     When working on algorithms it is very convenient to be able to easily capture raw sensor data from the Firefly Ice to use for offline development.  The Firefly Utility iOS app has a page that allows raw data to be recorded and synced to your iCloud account.  From iCloud it is easy to access that data from your Mac.

    Checkout the Raw Data Capture page for details.


    SXSW 2014 Workshop: The Complete Hardware Crash Course

    Posted by denisbohm on February 06, 2014. 0 Comments

    I'm looking forward to holding a workshop at SXSW 2014: The Complete Hardware Crash Course. It will be on March 11th at the AT&T Executive Education and Conference Center.

    The workshop will cover the complete process of creating a small low power connected device by leveraging open source hardware and software. This includes electronics, mechanical parts, firmware, software, FCC testing, production, and more.

    You must signup in advance to attend SXSW workshops.  To reserve a seat, please go here:

    Hope to see you at SXSW!


    Firefly Ice Blue: Test Fixture

    Posted by Denis Bohm on February 05, 2014. 0 Comments

    The test fixture is used during production testing and programming.  It has spring loaded pins that make contact with the test points on the PCBA.  A plastic adapter holds the spring loaded pins in place and guides the PCBA into place.  This design makes it easy to momentarily hold the PCBA in the test fixture while the testing and programming take place.  The test points are brought out to a standard JTAG SWD connector, USB connector, and battery connector.  There is also a reset button.

    The following image shows the test fixture with and without the PCBA in place:

    Firefly Ice Blue: Production PCB Assemblies

    Posted by denisbohm on December 09, 2013. 0 Comments

    The first production batch of 1,500 PCBAs have been completed and tested. It's pretty exciting to see a few boxes of components turn into completed assemblies!


    3,000 Components

    3,000 Components


    Complete PCBAs

    1,500 Complete PCBAs

    Firefly Ice Blue: FCC Testing Completed

    Posted by denisbohm on December 09, 2013. 0 Comments

    Firefly Ice Blue has passed FCC testing!

    Here is the Firefly Ice on the clear plastic table in the RF anechoic test chamber (tiny black device in the lower right):



    RF Anechoic Chamber

    RF Anechoic Chamber


    If you are thinking of making a product with a radio there are a couple of things to keep in mind when designing your device to make things easier when the time comes for FCC testing.

    1)  Make it easy to bypass the antenna and matching circuit to bring out the RF signal via a 50 Ohm SMA connector.  This allows the device to be directly connected to a network analyzer as required for a number of tests.



    2) Prepare test software to place the Bluetooth 4.0 radio into Direct Test Mode (see the Bluetooth Specification) with various parameters.  You will be asked to put your device into a direct test mode and transmitting on various frequencies, so make that easy and quick in your app.

    iOS App w/ Radio Direct Test Mode

    3) Bring a couple of chargers and computers to use with your device for measuring conducted emissions.  Since your device is so low power, you will actually be mainly testing the chargers and laptops conducted emissions rather than your devices.

    Conducted Emissions Testing

    Firefly Ice Blue: Core Plastics

    Posted by denisbohm on December 09, 2013. 0 Comments

    Firefly Ice Blue core molds are ready!

    The molds have been through a couple of rounds of tweaks and sample runs.  These are the latest plastics samples:

    These are the plastic parts after assembly:

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