Good news! We have resolved the reset issue, and sent off files for manufacturing. We should have the first test batch of 10 Tessels in our office next week. As soon as we’re done testing those units, we’ll pull the trigger on manufacturing the first batch. If all goes well, production will take 1.5 to 2 months.
Here’s a render of the new boards, sans through hole components:
If you’ve been checking out Tessel’s old layout, you might notice that we changed quite a bit in the lower left hand corner which contains all of the power conversion stuff.
Since we had to rework Tessel’s schematic to fix the reset issue, we decided to upgrade the power handling circuits while we’re at it. In short, we’ve switched from a linear regulator to a buck regulator. Here’s a handy chart to see what this means:
|Parameter/Thing||Old value||New value||So what?|
|Voltage regulator type||Linear regulator||Buck (switching)||More current available on the 3.3 V rail, higher efficiency|
|Max current from 3.3 V rail from USB 2.0||~500 mA||~750 mA||More current available to modules!|
|Max current from 3.3 V rail when running on appropriate external power||1 A||3 A||So. Much. Current.|
|Maximum input voltage||5.5 V||15 V||Tessel can be powered off lots of different kinds of batteries. Or even stack your batteries for extra fun.|
|Reverse voltage protection||8 V||20 V||Now we can be extra sure that Tessel won’t die if you plug in the power backwards.|
Note that increasing the maximum possible/available input voltage and output current doesn’t mean Tessel will necessarily consume more power, but rather that Tessel can now make better use of the power it draws. More specifically, upgrading to the switching regulator means we’re automatically about 20% more efficient than we were before under all conditions.
All our best,
Kelsey, Jia, Eric, Tim, Kevin, and Jon