Thermal
Early designs used a linear regulator to supply 3.3v from the Newton's battery voltage. It became pretty obvious that a linear regulator would get too hot, and so I changed it for a switching regulator.I wanted to do a real world test. The WiReach specs say that it can draw around 350mA peak during transmit. I modified the Thumb sample code into a program that would output a continuous stream of ~25kB packets. I taped a thermocouple to the regulator and ran the test for an hour or so.
The results were promising. From room temperature, the regulator went from 77.4F to a high of 85.1F. This satisfies me that in my normal use the board will not overheat.
A wise man once told me:
"People might be using such a Newton on a camp site close to Death Valley in August. Before you release such a circuit into the wild, you should put the assembly into the baking oven at 60 degrees centigrade and see what happens..."Good advise, but I don't think I'll be performing that test. I just can't imagine putting a Newton in a oven for any amount of time.
This test is anecdotal at best, I guess. Was the WiReach module anywhere near its peak transmit power or current draw? I don't know. At 115200bps, I'm not sure that the Newton can saturate the WiFi module such that it would need to draw its maximum.
Physical
I found one other minor issue with the physical design. I intentionally pushed the module as close to the edge of the Newton as possible-- into the space where a telephone jack would have been for an internal modem. The module is large and getting it in just the right place and keeping the board within a 5cm square took some trial and error. Also, I wanted the antenna area as close to the edge of the case as possible.Well this made for one unintended consequence-- the "plug" that covers the hole likely won't fit, and it will interfere with the WiReach antenna connector and board. It isn't the end of the world really -- I intend to 3D print a new plug with a little more clearance, and maybe an embossed WiFi logo so you can tell from the outside that there's a WiFi card installed.
