I’m enrolled at the University of Calgary in an electrical engineering post graduate diploma program with the eventual goal of switching into the biomedical engineering masters program.

So far I’m taking:

• BMEN601 Fundamentals of Biomedical Engineering - an overview of the biomedical engineering field with focus on presenting and writing research papers.
• ENEL563 Biomedical Signal Analysis - looks at the characteristics of different biomedical signals and how to use FIR filters and statistical analysis in Matlab to isolate and identify features of interest.
• NANS301 Introduction to Nanoscience and Nanotechnology - An introductory course on nanoscience, nanotechnology, and nanomaterials.

There is a problem with high-efficiency LED drivers used for a lighting product. One of the final steps in the build is to reduce the current to a set point, but this is causing the units to start strobing on/off.

After testing the possible combinations of power supplies and product boards I was able to make the high-efficiency power supplies consistently to fail which pointed towards the power supply being the culprit.

The high-efficiency power supply stabilized when the current was raised above the desired set point of 1.08A to 1.29A. After the fixture & electronics warmed up, it would start to strobe on/off again unless the current was again raised to 1.40A. The power waveform on the oscilloscope showed the unit powering up, holding steady for a moment, dropping down and then powering back up again in a cyclic pattern. The puzzling part was that performing the same test with a 48V standard efficiency version of the driver didn’t cause strobing.

It turns out that that the design was under driving the supplies by providing only 36V when the data sheet required between 40V-50V. This was tripping the short circuit protection on the driver causing the unit to reboot.

While I suspect that component vendors add slack to their data sheet tolerances you are asking for trouble when you disregard them.

I’m having problems while trying to do a power test for customer’s board. The voltage measurements I’m reading on the +5VDC test point is too high (5.43VDC) and the current draw during start-up was 49.2ma when it should have been around 30ma.

I removed the driver and wired it directly into the power supply by soldering some jumper wires to vias in an attempt to narrow the problem down to the component or the PCB itself. After doing this is started working normally.

The customer put down two overlapping sets of component footprints so they could build the board with two different driver components and the driver’s metal case is shorting on the unused pads :-/.

Today’s corrective action = add tape.

I’ve been stuck on a problem with a tester for a digital signal processor board we build for a customer.

The failing test isn’t even one of the complicated ones. It’s just looking for the proper voltage on a control line. For the test, the DUT is re-booted to manufacturing mode, sent a control signal on the RS232 port which raises this control line to ~12 volts. On boards that were failing the DAQ card was reading low voltages and sometimes no voltage.

The puzzling part is that when I re-test the same boards they will start passing. On multiple occasions, people set aside stacks of failing boards and when I come over to look at them they pass.

By accident, I noticed that test set (customer supplied) is probing a via on the board instead of a proper test pad. Normally that wouldn’t be the end of the world but we started solder tenting vias near the power supply to prevent flux from coming up through them during wave soldering process and being left on the top of the board. The tenting is preventing the probes from making contact during the initial test but scraping off enough material that when I come over to re-test them they start passing :-/.

I’m not sure exactly how much time was wasted between myself and the customer on this one but it was more than they saved by cutting corners by probing a via instead of designing a proper test pad.