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.
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.