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.