Sylvie the Awful Pony
12-23-2013

Sylvie spent most of her life leisurely grazing on wall to wall carpeting and conversing with the other toybox denizens about the disappointing state of televised entertainment. Her owner was a quiet girl who would craft lavish adventures for Sylvie to experience. Until she grew older, and much bolder. The plastic horse was left on the curbside in favor of taking a motorbike and Casio CZ-101 to the edge of the world. Sylvie understood, but still felt abandoned...

...until we found her for $5 at a used toy store and filled her empty heart with similarly discarded electronics. Sylvie features speech playback and dimmable red eyes both controllable over bluetooth. While these are very simple in theory, Sylvie was built as part of an ongoing garbage challenge to convert scrap electronics into mildly interesting devices. This usually equates to lots of grey wire protoboards filled with components running out of spec.

Design Materials
PIC16C73 Source For Microchip MPLAB v8.92.
PIC16C73 Binary In Intel HEX Format.
Board Notes So you can build your own demon pony.


Protoboard Puzzle

As a shining example of a boring toy for girls, Sylvie had only one point of articulation, her neck. This was also the only point of entry for electronics, since any large incisions would immediately give away Sylvie's demonic nature. Therefore all of Sylvie's functionality had to be divided into the various boards shown to the right. These were inserted one by one through the neck, then carefully reassembled.


Way Past Spec

As the price of 3.3v SPI Flash memories was next to nothing, Sylvie was made to run completely off 3.3V power aside from the battery charging circuit. This caused problems for two components, in particular the PIC16C73 microcontroller used for her brain and the DAC-08 for her voicebox. The PIC16C73s I found in the bin were spec'd to operate with a minimum VDD of 4V, but about 60% of them could tolerate 3.3V.

The real challenge was the DAC-08. For those not familiar with the component, this is an older parallel DAC which requires a bipolar supply of +/-10V or more to operate comfortably. Using a unipolar 3.3v supply results in heavily clamped output with the transition area far too distored to be useful. However, I found that by reversing the Vref pins (pulling Vref- to +3.3v and Vref+ to GND) a sweep from $00-$FF on the DAC would result in the waveform shown to the left.

As Sylvie was one of the first users of the MEMPAK format, generation of a sample adjustment table based upon a logged amplitude sweep was added as a packing option. Sylvie's sweep data is available here.


All content by Osman D. Celimli unless otherwise noted.
Not all of said content guaranteed to be useful. Some is probably quite old and dumb.