Photo by Jonas Denil
Technical

How We Took an LED Coaster From Concept to Production in Two Weeks

It is with great sadness that we saw the recent departure of Adam, one of our longest-serving team members, from Mindtribe last month. He was such a large part of the team and there was no way we were letting him leave empty-handed. This is the illuminating (ha, pun intended!) story of how we took a special gift from concept to production in just two weeks

DISCLAIMER: This is not for the faint of heart! You will hear of tried and tested core design principles being disobeyed, blood-pressure raising schedules and an MVP being redefined as the maximum viable product. Take this as an example of why we have these practices in place.

T-Minus 16 Days Until Adam’s Departure: Concept Generation

It’s no secret at Mindtribe that I have a particular penchant for lasers and LEDs. I had recently discovered some RGB LEDs which are just 1x1x0.65mm – that is the definition of crazy small. This, combined with an LED matrix controller from ISSI, made for an interesting weekend project of mine. The result was an 8×8 RGB LED matrix that measured 16x16mm. Showing my latest flashy LED widget around the office got some “oohs and aahs,” especially from Adam. Who isn’t mesmerized by rainbow fades?!

For the Mindtribe holiday gift last year, we created a custom PCB coaster. There was no circuitry involved, but it was always a pipe dream of mine to put a load of LEDs on it one day…

An idea was brewing: an illuminated LED coaster.

concept to production

T-Minus 13 Days: Architecture Definition

By this stage in a typical project, we would have boards out to fab (if not already back to us), bringing them up and documenting the system. For this time-sensitive project, however, we started at architecture definition.

We had decided on the LED controller and 128 tiny RGB LEDs but not much else. After brainstorming with Timothy, browsing through Digikey’s website, and using some of our favorite parts, we nailed down our component selection:

  • STM32L433 microcontroller for its insane low power modes
  • LIS2DH accelerometer for interaction
  • 4x ALS-PT19 ambient light sensors for brightness control
  • BQ24040 LiPo charger with USB input
  • 2Ah LiPo battery to provide plenty of run-time
  • TPS61032 5V boost for the LED supply
  • TPS62740 1.8V buck for MCU and support circuitry
concept to production diagram

The super-official block diagram, drawn in my favorite CAD package.

T-Minus 11 Days: Design Review

With components selected, it was time for us to create parts in Altium Designer, drop them into a schematic, and wire them up. When a design has to progress this fast, there are inevitably some oversights. To help alleviate any design flaws, I rounded up some unsuspecting victims at lunch the following day to have a quick design review to ensure we got the boards right on the first try.

T-Minus 10 Days: Board Layout and Manufacturing

As it turns out, with 128 RGB LEDs, you have a lot of wires to route. The board turned out to be 4-layers with dense busses of traces weaving between all the LEDs. 76 LEDs are arranged into the Mindtribe logo on the top and the remaining 52 are arranged along the edge of the back to create an underglow.

PCB Concept to production

Four layers of pretty dense PCB tracks. I love a good routing challenge!

Our choice of manufacturer for this projects was JLCPCB. They are insanely cheap, and a very fast and good quality supplier based in Shenzhen. What we didn’t count on, however, was that they had just returned from a 3-day holiday and naturally, had a 3-day production backlog! We sent off the design files anyway, hoping they’d be back on time.

T-Minus 8 Days: Rapid Prototyping

While we were waiting for the PCBs to come back from fab, there were plenty of other parts to get started on. Timothy had already made a great start on the firmware with dev boards and it was time for me to put on my Mechanical Engineering hat!

This coaster had to be robust, so we decided on a design using milled polycarbonate to clad the PCB core of the coaster. We have an Othermill at Mindtribe and this was yet another occasion we used it for quick turnaround jobs with great results. The top plate was milled to create pockets for the LEDs to diffuse into and the bottom had a pocket to hold the battery.

Rapid Prototyping

The polycarbonate top fresh off the mill.

A couple of iterations later and the parts were ready for the electronics.

T-Minus 2 Days: Receiving Electronics

With 2 days to go, we didn’t have electronics – we didn’t even have bare PCBs. The fab house had a series of delays that held up our boards.

Kerry and I both order quite a few things from China and have become experts on the intricacies of DHL. I watched our PCBs go over the border into Hong Kong and even found out which flight they were on. They were scheduled to land in LAX Thursday morning, switch over to SFO, and then be on a truck to be delivered to Mindtribe by the end of the day.

T-Minus 28 Hours: Testing and Debugging Electronics

We received the boards Thursday afternoon and went straight to the lab: squeegee-ing the solder paste, hand placing all 150 parts, and sticking it through the reflow oven I borrowed from Kerry. We checked for shorts, ohm-out some crucial nets to make sure there were no faults and applied power! Thankfully, magic smoke safely held inside all components.

Electrical components

Halfway through part placement. Surprisingly therapeutic placing lots of tiny components.

Then we programmed Timothy’s test firmware – this was the moment of truth to see if our design would work. Unfortunately, it didn’t.

The wonderful world of hardware development can often be brutal and throw you a curveball when you least expect it! After some debugging, we were completely stumped. It seemed like there was a problem with the accelerometer.

T-Minus 7 Hours: Further Debugging and Product Launch

With just 7 hours left, we approached the challenge with a fresh pair of eyes. A few reflow attempts on the accelerometer got that working (the LIS2DH comes in a rather unfriendly LGA package) and some ninja debugging from Timothy and boom, we had our LEDs working!

Concept to production

A couple tweaks to the accelerometer settings, a custom foam insert created to present it and even some power analysis and we finished it!

Using our N6705C DC power analyzer, we characterized the power consumption and found our sleep current to be a mere 4uA with the 1.8V rail running, MCU in sleep and accelerometer active. That gives a theoretical sleep life of 57 years on our 2Ah battery! Of course, this doesn’t account for the self-discharge of the battery or that fact it will probably have decomposed by then.

During the emotional farewell gathering for Adam, we presented him with the coaster. Almost surprising ourselves more than others, we had actually done it! A project from conception through design, manufacture, build, test and delivery in under two weeks.

It’s a core principle of Mindtribe to create the MVP first and to set realistic schedules and Adam embodied this every day. This project didn’t exactly adhere to these principles. Still, we somehow managed to deliver!

It was our honor to create something special for Adam to remember us by.

Team result

Freddie, Adam, and Timothy with the coaster