Grr! Apple has updated the firmware and USB handling on all their new iPods (and upgrades) so that they do not play with Mintyboost so nice. There’s a simple fix on the Mintyboost site, (just moving a resistor) and this will be updated in MintyBoost v1.2 which is in the works as we speak!

This saturday, I’ll be running 2 workshops for 10 people each wherein we build a mintyboost kit. The event is the EYEBEAM 2006 Hackshop Sign up today & bring a gum tin to put your charger in!

Shown above, a HOPE attendee builds her mintyboost mere minutes after purchase.

Its like post-cyber-retro action in here, with the new clear acrylic panels available for the x0xb0x. These are cut and etched using a 35W lasercutter for precision & good looks. New x0x orders can add this, older x0x users can grab a set for $30 from the adafruit webshop.

The silkscreened panels came in today, that means we’re doing run #5! Just in time for xmas…

Now that i’ve finished porting icky C++ code I can return back to thoughts of sweet sweet hardware design. Next up is a second MIDIsense board.

The next board is pretty simple: An analog and digital IO board. This is what most MIDI interface boards are used for. The atmega8 chip has 6 10-bit analog inputs so there will definately be 6 analog inputs. Then I decided to put in 5 digital I/O too. Not only will you be able to get digital inputs (switches) but also control the pins as outputs including PWM outputs. OK not very interesting, I admit.

So then I thought about improving that a little bit:

For the 5 digital I/Os, instead of just having the pin go to the microcontroller and thats it, I put in spot for installing a capacitor to +5V and a series resistor. (To install the resistor a trace must be cut).

Of course, the RC pair can be used as an output filter: so that PWM output can be smoothed out nicely (the output will be PWM’d at around 16Khz)

The resistor can also be used to choke the output, for driving an LED for example.

But of course the real trick is that now the board has 5 extra analog inputs for measuring resistive sensors: by setting the output of the pin to +5V (discharging the capacitor, its tied to 5V) and then measuring how long it takes for the capacitor to discharge through the resistor! Its a poor method of measurement and takes a while to get a stable result (as compared to the onboard A/D). However, it certainly works and for many situations, and its good enough for most MIDI sensor applications where the 10-bit A/D may be overkill.
(You can read more about the RC timing A/D trick from this old-school app note from phillips although its rather outdated, you can get an idea of how to implement it!)

So now the board has: 11 Analog inputs, or 11 digital/PWM outputs (5 with RC filters).

If you wanted to try out the MIDIsense hardware but didn’t have a Mac, well I finally finished porting the wxpython code to C++ and its all much faster and more reliable. I also improved the interface and robustness. Try it out and let me know how it goes, available for download from sourceforge

I make kits so I’m always interested in seeing what other people have up their sleeves. For my bike stereo last year I used 2 class-d amps based on the TPA3001D (1 x 20W). This year, I bought 2 AMP3 kits from 41Hz. Each kit drives 2 x 25W which is perfect since I have one speaker on each handlebar. They are designed to run on a 12V SLA battery (up to 14.5V input).

Stuff I liked about the kit:

• Silkscreened, soldermasked PCB for easy assembly
• Lots of thruhole vias, heavyweight copper
• Winding the toroids was totally painless
• Chip works great!
• Has a configurable pre-amp that is good enough to take line-level input

Stuff that was a little annoying

• PCB came with copper shorts, apparently a fluke but still frustrated me
• 0805 parts: Why? 1206 would be much easier! (Jan says the particular resistors were thin film and only available in 0805 although I’m still a little suspicious…)
• Output connection and power connection is adjacent for no particular reason, and holes are much too small for speakergauge wire. I think having large speaker-style terminal blocks for the speaker outputs would be a reasonable design upgrade.
• If you’re going to use 2oz copper, have thermals! Soldering this requires a very powerful iron which also needs to have a fine tip. That’s a bit of an oxymoron.

Overall: I give this kit a B+ Its a great design, with only a few technical issues. At $25 for 2 channels of 25W classD action, its a mega-bargain!