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circuitfantasia

Filed under: EE,random — by ladyada, posted August 22, 2006 at 3:02 am

Bike Stereo

Sometimes its really important to have a stereo system for your bike. SCUL has a ‘standard’ method by which they use a 12V SLA hooked up to a car stereo which is then wired to some car speakers. It’s cheap and easy but I’m never one to leave well enough alone. Thus my ultra-light/ultra-efficient pimped-out bike stereo system:

  • 2 x 7.4V 4Ah Lithium Ion Camcorder batteries = 15V at 4A = 60W of power! ($20 each)
  • Class D amp. I use the TPA3001D1 you can get kits for this, I made my own PCBs cause I wanted to make at least 4 amps. Either is A-OK. up to 20W output! Is TSSOP so a pain to solder.
  • Cheap MP3 player (this one was ~$10, uses MMC cards and a AAA battery) You dont want to get your iPod all dusty. Requires an MMC card, a 256M is like $25 or something.
  • Speaker(s)! I recommend old car speakers. Making an enclosure for them will make them sound better but they’re sort of engineered for poor enclosure design. Cheap/thin cookpots work great and come with an attachment point even!

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Filed under: EE,projects — by ladyada, posted August 17, 2006 at 2:11 am

Reverse engineering the Mac ‘breathing’ LED

For the Duel nature sculpure, I wanted to have a ‘breathing’ pattern where all the LEDs vary in brightness in a natural/organic way. A good example is the ‘sleep indicator’ LED on recent Macs/Powerbooks. (There’s even a patent!) The problem is that, while the patent claims its a simple sinusoid (see the patent for the image), programming in a sinusoid doesn’t look nearly as good. So I decided to get the real waveform with a kludgy reverse engineering attempt:

I used a MIDIsense instead of a simple voltage divider because I want to extract the absolute LED brightness pattern and a photocell voltage divider acts ‘inversely’ (well, 1/R) instead of linearly (ie, just R). (The MIDIsense has an opamp to linearize the resistive sensor output)

There it is! There is a bit of ‘noise’ on the peaks because I’m picking up some of the PWM artifacts through the diffused white plastic.

Filed under: duelnature,random — by ladyada, posted August 11, 2006 at 12:52 pm

Duel Nature: Time to bake the PCBs! (How to make PCB reflow stencils)

OK so boards came in, and there’s 80-100 to be assembled. They’re pretty simple boards: 1 8-pin micro, 3 resistors, 1 capacitor and 2 4-pin header plugs. Since it takes a long time to solder, I designed the board for mass-manufacture: surface mount parts!

Eventually everyone needs to make a lot of PCBs (at home), the best way to do this is to use solder paste and a reflow oven. Since EYEBEAM has a laser cutter I can use it to make a screening stencil and a registration frame. (You can also buy stencils from your 4pcb.com and probably a bunch of other PCB manufacturers) Then it’s super fast to make tons of PCBs. Just silkscreen on solder paste (available at digikey), place the components, and bake!

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Filed under: duelnature,EE,projects — by ladyada, posted August 1, 2006 at 10:57 am

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