All posts tagged "hardware"

It's alive!

Rev2 is up and running, blinking and blending away on Ishani’s desk.

After much cogitation, it would appear I swapped data in and data out to the MAX6960 while swapping pins in the firmware to match the new board layout.  I can never remember from which perspective those are supposed to be interpreted.

As always, there are still some issues with Rev2:

  1. When it is turned off but plugged in to USB the display still runs.  It appears to be a case of power being pushed through the clamping diodes on the AVR.  It’s either the USB interface (which is bus powered) or the charge indicator (which is foolishly connected directly to the bus power.  Regardless of the cause, it means that when plugged in to USB it should either be switched on or have the display disabled in firmware.
  2. The buttons are ridiculously small, so much so as to be completely unusable.  Future revisions will replace with a single, larger button.
  3. As mentioned before, the strap tabs are on the wrong way around and obscure the switches and USB connection.

Pushing forward with Rev3 (which should be renamed as it shares very little with the previous designs) in the meantime.

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We are experiencing some delays getting Rev2 working.  It passes all of its self tests with the exception of the display.  Communication between the two boards appears to be the same as with Rev1 but fails to produce an image. Pleased to have my logic analyzer around.  Beats the hell out of chicken guts or tea leaves for figuring out what’s gone wrong with inter-chip communication.  There may be subtleties to timing that I have missed.

We are experiencing some delays getting Rev2 working.  It passes all of its self tests with the exception of the display.  Communication between the two boards appears to be the same as with Rev1 but fails to produce an image.

Pleased to have my logic analyzer around.  Beats the hell out of chicken guts or tea leaves for figuring out what’s gone wrong with inter-chip communication.  There may be subtleties to timing that I have missed.

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Mostly assembled.  Waiting on the USB to serial IC.

Mostly assembled.  Waiting on the USB to serial IC.

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Some fresh circuit board pr0n.

Some fresh circuit board pr0n.

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Rev2 boards are on their way to be fab’d. Much cleaner main board design with lots of test points on the back for programming and testing with a pin jig. Added missing pull-up resistors on the i2c memory bus. Removed the fancy (and expensive) navigation switch in favor of two bog-standard SMD pushbuttons. Added fancy tabs to the display board for a mounting strap of some sort. The fab house doesn’t do inside routing, so I stacked a bunch of drill hits to make the slot.  Hope it works out..

Rev2 boards are on their way to be fab’d.

  • Much cleaner main board design with lots of test points on the back for programming and testing with a pin jig.
  • Added missing pull-up resistors on the i2c memory bus.
  • Removed the fancy (and expensive) navigation switch in favor of two bog-standard SMD pushbuttons.
  • Added fancy tabs to the display board for a mounting strap of some sort. The fab house doesn’t do inside routing, so I stacked a bunch of drill hits to make the slot.  Hope it works out..
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A quick snap of the Rev1 prototype; Although it’s already pretty compact, John estimates we can shave a 1/3 off the height on the next revision.

A quick snap of the Rev1 prototype; Although it’s already pretty compact, John estimates we can shave a 1/3 off the height on the next revision.

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Battery Operation

Things got really hot when I soldered in the battery this morning.  Turns out I’d made a silly mistake wiring the charging circuitry.  If the battery hadn’t had it’s own overcurrent protection, we might have had a pretty nasty fire.  Anyway, one pin-lift and the device is now free-standing.

In other LED news, check out these fancy LED invitations.

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Back to the drawing board...

The microcontroller board just has too many errors to continue.

  1. The flash memory is in a SOIC-wide package and barely fits on the pads.
  2. I forgot the pull-up resistors on the memory as well, which requires a very fiddly green wire fix.
  3. I didn’t include a programming header for the AVR, which seemed like a good idea at the time.  It was not.

At this point, the amount of time it will take to get it working with the current board revision is just too much.  I’ll be making those changes to the design and sending the boards out for another round.

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