November 2011 Archives

This circuit is based on the TDA7350A by ST, which is a robust car radio amplifier.  It supports 22 watts of bridged output, which is then sent through a 50'+ underwater umbilical, into a dive mask.  The line matching transformer is actually milspec; it was the only one which fit the bill!  The current version is hand wire-wrapped and placed within a NEMA box.  But though sealed and packed with desiccant, everything electronic is mortal in a saltwater environment.  With PCB's in stock, we'll be able to quickly produce new units.  This first revision is a bit spacious, the next one will likely have two units in the same panel space.  The panel pins will also be better utilized i.e. for the pot header.

This is what happened to the original board:

yes, not the nicest looking circuit...

Recently Jon Britton and I participated in the Educator Extravaganza, in which we delved into the electronics at our jobs, and gave educators a peak under the hood.  One gizmo we left people with was the CdS Transistor candle, pictured above with the lamp gone all bokeh.

It's essentially one of the simplest and most educational circuits that can be made, without handtools, solder or even a breadboard.  For me, its entirely magical, and goes the distance at instilling an intuitive understanding of electronics.  According to one high school physics teacher, it even fit a state standard to explain "how transistors work."

I've attached the lesson plan with bill-o-materials and procedure (scrambled together, errors and all, half an hour prior to the event) here:  eextrava.pdf