New Speaker Design

Snapshot of work in progress on new speakers. Intended as platform to test speakers, enclosures, ports, cross-over networks, filters, and amplifier designs.

IPM Module Failure

After rebuilding using the other IPM module and additional FET's, we experienced a second very loud failure as seen in this short video. The camera runs at 15 fps and the explosive incident is only visible, very brightly, in one frame.

Extension Assembly for IPM Module

To facilitate repair and testing, we've turned the heat-sink/IPM module on its side, added another heat-sink on top for external FETs, and temporarily mounted this to the Y sustain board. During testing, we encountered a failure (visible short on die) in one FET on the remaining healthy IPM module. We are now hand wiring high power discrete FETs (two seen on the left in this photo) taken from the other TV externally to substitute for the on-module devices. In one test, we experienced a very loud and spark-filled explosive failure destroying the remaining on-board FETs, some surface mount resistors, and the external FETs. We've rebuilt this assembly with the other IPM module and additional high power FETs; test results shortly....

Pop Goes The Plasma

It is hard to consider the odds but within a 5 day window, we obtained two LG 50" plasma tvs from the local transfer station (120 pounds each!). From what we've been able to read on-line, these models have a class problem with early failure (within 9-24 months) of the IPM modules on the Y and Z driver boards. The near universal problem description is a "pop" followed by loss of picture but with sound still available. This photo shows the likely source of the pop: two large dies mounted on the primary Y module surface have clearly failed catastrophically. If you double click on the image, you will see an interesting close up of the surface and the explosive nature of the phenomena-nice craters. The good news is we were able to harvest another identical and healthy IPM. Our challenge is extraction and re-installation on the boards. We have found it very difficult, requiring very high heat to remove the modules, in some cases damaging the fragile top traces and surface mount components. We removed the same module on the Y board out of the second LG TV and found all four transistors had failed in a similar fashion.

High Current 12 VDC Supply

This is a new power supply built from a transformer and rectifier (mounted on the aluminum heat sink) taken out of an industrial control-timer of some kind. The black transformer is a heavy duty winding that appears to be rated at over 11amps on the secondary. In this first use, we were able to drive 8 amps through an electrolyte solution of sodium bicarbonate and sodium chloride in a new electrolysis cell with four aluminum bar electrodes. Of course we had to test for flammability....

Attention to Form

The landing was surprisingly good!

More snow.....and cold!

Stamp interface to Allegro Motor Driver

This is a very successful project David has underway that uses a UDN2916B motor driver IC out of a printer to control a bipolar stepper motor with a Stamp micro-controller. It demonstrates very accurate discrete control of the stepper motor via parametric changes in variables in the code. Our plan is to create a board layout and use an outside service to produce a printed circuit board. The next step is to scale the architecture with a two-level multi-Stamp model to control multiple boards.

Data from Air Cannon Velocity Timing Measurement

This is a very interesting graph of data we collected using the same cork as the pressure in the feed tank (bottom trace) declined with each firing. The time (count) pattern shows erratic performance and slower speeds at very high pressures followed by a dramatic increase in cork velocity at about 40psi. A fairly stable and smooth curve from 40psi to 20psi where the speed then falls off to a new regime at slower speeds. For perspective, 146 f/s = 100 mph. Double clicking on the graph will bring up a larger and more readable view.

Timer Update & Initial Success !

Completed assembly with with IR LED and photo transistors (two additional transistors tied with the photo transistors in a Darlington configuration drive negative pulses are on breadboard to the right) harvested from small circuit board position detectors (Omron) and mounted 24" apart in the PVC barrel seen at bottom of photo. Wiring between barrel and circuit board uses a standard cat5 connector that can be used for extension) Running the clock at 93Hz measured (end counts on display of 4 and 5) and 8106Hz calculated (end counts of 377, 433, etc), we fired a cork under human air pressure and found consistent results measuring speeds between 37 and 46 feet/second. We'll hook up the rest of the air cannon and air tank after lunch! Hard to see but the blue decoupling caps are from my days working at Raytheon....some time ago...