ARM Investigations


My cat has been telling me she wants to get more into 32 bit ARM processors. So when ST started freely offering their discovery development board for their new Corex M4, I jumped at the chance. My luck was in and the board arrived today! The STM32F4 on the board has a full meg of flash and a single precision floating point unit! Oh and like a bazzilion hardware timers and lots more. The board itself has a number of sensors and a big LED on it.

My cat is looking forward to spinning up a compiler and putting the device through its paces. She is especially looking forward to the demo app where the board pretends to be a mouse.

Thursday Night Time Lapse

A time lapse video complied from the Milwaukee Makerspace CCTV system. 7 hours of video compressed into 4 minutes. All events took place between 4:30 and 11:30 PM Thursday, September 29, 2011.

Activities include:
– Rich welding
– Chris and Rich working on their electric cars
– Chris driving his electric car in and out of the shop
– Tom, Adam, and Royce working in Diptrace
– Bret, Rich, Royce, and Adam blacksmithing items with the forge
– Various people working on misc. projects and chatting
– Royce, Brant, and Adam etching and tin-plating circuit boards
– Pete working on his Makerbot 3D printer

Builder’s Night Out – September 29th

In addition to the usual hackery and makers working on their electric cars, Bret fired up the forge again last night.  Rich turned some horseshoes into hangers, Adam flattened a steel rod, and Royce folded a metal bar.

In preparation for BarCampMilwaukee6 (this weekend!) Royce and I have been mass producing circuit boards for a “learn to solder” class we’ll be holding.  The boards are 1.5″x1.5″ square and include a battery, two resistors, traces in the shape of our logo, and two red LEDs for eyes.  The copper traces were tinned using “Tin It” to prevent oxidation and make it easier to solder.  We’ve made 65 of the “tie pins” so far and the project gave us an opportunity to tweak our methods for PCB etching.  We prefer etching with ferric chloride, but muriatic acid and hydrogen peroxide are looking more attractive as they’re cheaper chemicals, can be obtained locally, and etch much faster without heating.  Also, red Sharpie markers seem to work really well at cleaning up traces with the muriatic acid solution.  Specifically red, not sure why.


Tie Pin Prototype.


This is the prototype of the tie pin we plan to make for our own little Learn-to-Solder sessions. It’s inspired by the Makershed tie-pin. We don’t have any RGB flasher LEDs at the moment, and won’t in time forb BarCamp. But the red LEDs still look pretty cool.

At some point we’ll put an order out to a real PCB shop and get a circuit board with red solder mask and black silk screen. But these boards are plenty of fun for now.

Redwood Audio Amplifier

A few months ago I started collaborating with Jordan Waraksa on a project that is currently on display at the Haggerty Museum of Art, in a show running until the end of December.  He sculpted a pair of wooden acoustic horns called Bellaphone 5 & 6 out of walnut.  Each horn rests on a redwood base that houses a small speaker.  If you visit the Haggerty, you’ll hear the speakers playing songs by Jordan’s band, The Vitrolum Republic.  If you really love the Bellaphones and amplifier, know they are for sale.

I developed and built the electronics for the horn’s amplifier, whose chassis Jordan also sculpted from redwood.  Because the chassis is wood and has no vents (for aesthetics), electrical efficiency became a high priority in order to prevent overheating.  I chose to use a Maxim 98400A class D amplifier driven by a high efficiency switching 15V DC power supply.  I added a digital signal processing chip from Analog Devices to increase the bandwidth of the horn and smooth out its frequency response (i.e. to improve the audio fidelity).  Analog’s ADAU1701 is a remarkably powerful chip – it is more than capable of these tasks.  In addition, the 1701 prevents bass notes (frequencies below 100 Hz) from reaching the small speakers (which are incapable of reproducing these low notes), which would otherwise emanate from the horns as distortion.  Finally, the 1701 also adds a small amount of compression, which prevents distortion at the loudest output levels.   The 1701 is actually real-time programmable via a USB connection to a computer running Analog Device’s free SigmaStudio software.  It’s a tremendously user friendly GUI environment with drag and drop audio processing blocks.

Check out the inside of the amplifier as it was being assembled, prior to the addition of many ferrite beads which eliminate the audible noise from the three high efficiency switching power supplies:  One powering the amp, one powering the DSP board, and one continuously charging a Motorola Cliq XT handset playing songs from the Vitrolum Republic.

Here are two more close ups, one of the amplifier:

And one of Bellaphone five and six:


I’ve recently made several audio synthesizer / noise generating boxes.  The most recent is the Cacophonator, whose circuit description and board layout are easy to find on the web.  Thanks to Adam for showing me how to etch my own circuit boards – something I can now do quite easily at the Makerspace.  I modified the board layout, drawn in DipTrace, so I could add SIP sockets and pin headers to tidy up the inside of the project box.  The sockets also allow the board to be easily removed, despite the 20 wires running between the board and other components inside the project box.  The  photos below were taken before I modified the circuit by adding a momentary power switch to slowly recharge the giant power supply capacitor if held for a few seconds.  I also added a LM317 adjustable voltage regulator so the power supply voltage can be reduced all the way down to 1 V DC and below.  The sonic complexity of this circuit is surprising considering its small part count, and lowering the power supply voltage further adds to the chaotic behavior of the cacophonator.  Careful inspection of the board will show additional components not associated with the original cacophonator, but are discussed on  These are used for inputting audio signals (music, for example), which come out the RCA jack quite cacophonated.


Carrie tests the GyroBelt

Tonight, at the Bayview Bash, Carrie tested out the GyroBelt to live Salsa music. As you may remember from previous posts, the GyroBelt is a prototype device for what will eventually become an eFashion skirt. The prototype and the skirt both try to avoid the Christmas tree effect by only illuminating the LEDs under certain conditions. Namely a high speed dance spin as detected by a MEMs gyroscope.

Gyro Belt Driver PCB

Pictured above is the driver board of the GyroBelt. In the lower right you can see the red SparkFun Gyro breakout board. Immediatly above that are the four transistors that lead out to the bus for the LEDs. (In addition to mono chromatic LEDs the driver board also supports RGB leds.) To the left of the Gyro you can see an ATmega168 running an Arduino sketch. Above that are a couple trim pots that I use to adjust variables within the sketch. Continue reading

Electric Watt Hour Meters!

American Science & Surplus is selling residential style electric watt hour meters. Awhile back I picked up this analog one from them for $14, but they also have digital ones for less at their tent sale going on this weekend.  I finally found some time to play with it and I managed to get it working.  I’ll probably turn it into a lamp or something!

Electric Watt Hour Meter

Electric Watt Hour Meter from AS&S

Electric Watt Hour Meter Disc

Electric Watt Hour Meter Disc

Electric Watt Hour Meter Connections

Electric Watt Hour Meter Connections