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A former colleague once told me that he wouldn’t let his little daughter play with Legos because he doesn’t want her to see the world as a set of standardized bricks that fit together in predictable ways. That got me thinking. I grew up playing with Legos, and I pretty much see the world that way. I’ve been wondering whether that’s a good thing ever since.

Case in point, when I was putting together a low-cost Bluetooth-MIDI interface, I was thinking Legos. I had three bricks: The electrical specification of MIDI, running at 5V; a KC-21 Bluetooth module, running at 3.3V; and a logic level converter circuit that would turn a 3.3V signal into a 5V signal and back. I only had to stick those bricks together and presto, low-cost Bluetooth-MIDI interface.

I didn’t think much of it until I showed the device to Andrew Tergis of Bug Labs. Andrew pointed out that my solution was a bit of a Rube Goldberg construction and gave me some advice on how to revise the MIDI circuitry so that the entire gadget would operate at 3.3V, eliminating level shifting altogether. Ultimately, the solution was remarkably simple, just changing a few resistor values and replacing the TTL hex inverter with a PNP emitter follower. This approach reduces the number of parts by half, and it works like a charm. I just didn’t see it because I had Legos on the brain. Then again, without the Legos mindset, I probably wouldn’t have tackled the project in the first place.

In addition to simplifications, the new design brings one major improvement, a 3.3V step-up converter. This converter will take an input voltage between 1V and 3.3V and turn it into an output voltage of 3.3V. In particular, it can be powered with one or two batteries, AA or AAA, regular or rechargeable, and the output will remain constant even as the voltage provided by the batteries declines.

The resulting circuit is shown above, as a breadboard prototype, as well as below. I’m pretty happy with it now, and I don’t think there’s much room for further simplification. I documented the circuit in Fritzing and added it to the btmidi repository. The way I set it up, it’s extremely flexible. Right now I’m running it with two AAA NiMH rechargeable batteries and an RN-42 Bluetooth module, but you can easily plug in different batteries and a KC-21 Bluetooth module, or you can use XBee modules instead. In other words, the new 3.3V MIDI circuit is a Lego brick, ready to be combined with other bricks.


5 Responses

  1. larry

    im a complete electonics novice, but the more i learn–the more i can accomplish; the more i accomplish–the more i want to learn.
    a vicious and exciting cycle.  i too grew up with legos and have that mindset as well.  i belive i would not have as great a desire to learn or solve my own problems without it.
    perhaps your friend can use legos to nurture his daughter’s development into a more complex approach to life.

  2. Brian

    Hi the lego comments are interesting. I am not sure if I have that mind set, as a result of playing with legos.

    In the end stable matter is a set of legos: the elements, there are a multitude of ways they can go together though. So many we have hardly scratched the surface in Chemistry. Also the idea of finite state machines is a powerful one.

    I would like to come out strongly in favor of thinking of things as boxes. This is the way to do complex design. Get something to work quickly when you have the desire, then go back and make it more elegant. While there is merit in looking at a block of marble and seeing the statue inside, not all design can and should be like that. Painters paint over paint and electrical engineers iterate design from off the self rapidly developed designs to elegant SoC integrations.

  3. jared

    Brian, if elements are Legos, sometimes it’s a bit hard to snap them together :-)

    Peter, what kind of DIN jacks are those that you can stick in a breadboard? The ones I’ve found so far have had pins too big to fit.

  4. Peter Brinkmann

    Hi Jared,
    I’m using DIN connectors from Jameco, manufacturer # GKC5P. They fit in a breadboard, but just barely. I probably wouldn’t try this unless you’re willing to sacrifice a breadboard for the project.

  5. stephen

    Hi Peter, Do you have and circuit diagrams for this project : )

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