The Positive Rail
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Debugging SPI memory: the WinBond W25Q80BV

6/26/2014

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I finally have a board without faults, lines uncrossed, chips soldered in place.  The memory seems to read, at first glance.  The display shows the test text.  It runs through the test cycle.  Cause for celebration.
But the next morning I come back and try it again.  And it dies after ten seconds.  Repeat.  It dies in three seconds.  What is going on?

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The in-house printed circuit board

6/19/2014

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The rat's nest of wires taunts me as I poke the soldering iron deep into the mess, trying to add a connection.  It teases me as I try to squeeze it into the project box with loose connections that I then have to dig through and find, painstakingly.  It confuses me with bad solder joints.  

But I am strong.  I learn how to use the Eagle PCB (printed circuit board) editor, with its symbols, devices, packages, net-lists and other arcana.  I untangle the rat's nest line by line, learning to love the 'ping' noise when I make a connection.  I have a piece of artwork on the screen by the end.  Ready to go.  Now, how do I make the PCB real? 


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Burning chips: The Texas Instruments DRV8662

6/12/2014

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The positive rail is at 4 volts.  The boost rail reads 3.54 volts, one diode drop, as I expect.  

It's been a long road to this point.  I checked the naked circuit for shorts between power and ground, that the capacitor was an open circuit, the inductor a short to the power line, and that the resistors were in fact 10K to ground, 820KOhm, and 15kOhm.  I applied fresh flux to the pads and got a 'fresh' chip from the desiccant-sealed bag.  I used a thermocouple on the chip to monitor the temperature as I soldered it in, being careful to hold the hot air nozzle a few inches from the chip for a minute to warm everything to 100C, then bringing the air gun closer and the temperature up to  ~200C, removing the heat as soon as I saw the solder flow.  I rechecked the connections for shorts.  This is the third attempt today.

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    Embedded systems, nascent markets and minimalist product development

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