Stripe PCB v0.1

The PCB is the electronic backbone for an interactive product. It connects vital pieces to each other. The Stripe PCB has to perform several functions: power the Carambola, connect Carambola to the LED strip, provide a USB port for future extensions and house connectors for programming and troubleshooting.

Stripe PCB layout

The Carambola development board

Carambola development boardThe guys behind Carambola, 8devices, sell a full-featured development board for Carambola. It does all the above, which is why the development board was used in the Stripe prototype #2. It takes an input voltage of 9V or higher and turns that into 3.3V for the Carambola and 5V for the USB port and other peripherals. It has an old-fashioned serial port, two wired network ports, a USB port and a small prototyping area. Perfect for the development phase, but for Stripe it does too much.

From 230V (or 115V) to 5V

The RGB LED strip runs at 5V. The development board takes a higher voltage (9V-20V) and turns that into 3.3V and 5V using two switching regulators. When the LED strip runs at high brightness, the 5V switching regulator has to provide so much current that it starts buzzing audibly. This can be solved by choosing the correct components and filters for the regulator. However, I chose to skip it completely and go for a 5V input instead. Many appliances in the home and office run on 5V, so adapters are easy to get. It also makes the PCB design smaller, simpler and cheaper.

From 5V to 3.3V

To go from 5V to 3.3V it’s tempting to go with a linear regulator. A cheap and tested IC, two capacitors and you’re done:
LM1117 Linear Regulator
The linear regulator takes 5V, outputs 3.3V and expels the rest as heat. The maximum efficiency of this circuit results from a simple calculation: (3.3V / 5V) × 100% = 66%. Meh. Time to look around for a more efficient switch-mode DC-DC converter. Although they are harder to design and cost more, a switch-mode DC-DC converter can have efficiencies that easily reach over 90%. My switch-mode converter of choice is the relatively new and inexpensive NCP3170 from ON Semiconductors. Thanks to the trend of semiconductor manufacturers making life easier and easier for electronics designers, all that is needed is a few capacitors, resistors and an inductor:

NCP3170 3A switching regulator
NCP3170 switching regulator. 3 resistors (R1, R2, Rc), 4 capacitors (C1-C3, Cc) and an inductor (L1). Not too bad, right?

Turning that into a schematic

Why all this talking about voltage regulators? Well, because apart from that there is not else much to the Stripe v0.1 PCB. Beside the schematic as depicted above, there are some pin headers, a USB port and two rows of female headers for the Carambola module:

Stripe PCB v0.1 schematic
Many connectors, plus the Carambola on the left

Design, order, solder, test

So, what’s next? Pour it into a nice layout:

Stripe PCB layout

Send the files off too Seeed Studio’s Fusion PCB service and wait for four weeks for the boards to arrive (yes, that long unfortunately…)

Stripe v0.1 bare PCBs

Fire up the soldering iron & hot air gun and be happy:

Stripe v0.1 PCB populated

On to version 0.2

Although the v0.1 PCB works as designed, some footprints don’t match exactly and the placement of some components is not optimal. Also, in the four weeks between ordering and receiving the PCBs a lot has happened in the design of Stripe. I’ve already identified dozens of new features and changes for revision 0.2 of the PCB, so expect more on this topic soon!

On this blog, I am documenting the design of an internet-enabled linear LED clock: Stripe. Want to know more? Have a look at all posts about Stripe, subscribe to the RSS feed or follow me on Twitter

One Response to “Stripe PCB v0.1”

  1. Miguel Martin

    Hello David,

    Very good job.
    I am very bad with soldering iron it is possible to buy a made board?
    What would be the cost of this?

    Thank you,
    Miguel.

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