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xyzzy

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Everything posted by xyzzy

  1. fon console using USB serial: My laptop doesn't have an old style RS232 connector so the simplest arrangement is to connect the fon's serial pins to an FTDI serial-to-USB converter. Here's a $15 item from SparkFun: http://www.sparkfun.com/commerce/product_i...products_id=718 Connect RxD, TxD and ground from the fon to this device (swapping TxD and RxD), connect with a USB cable to your computer and you have a virtual serial port. Most Linux distros will have the required drivers standard, but Windows requires loading of FTDI drivers: http://www.ftdichip.com/FTDrivers.htm Works great with my Vista laptop.
  2. Here's a switching 5V regulator offered on ebay that will take anything up to 24V input and has over 90% efficiency: http://bit.ly/tIUbd The cost is $4 but unfortunately the shipping from Shanghai is $10. I think they were pulled from some other assembly line as some identifying info on the PCB is scraped off. It works as advertised. Anyway, they're quite small and would fit in the pineapple easily and allow all sorts of battery options. To take it a step further, there's a little trimpot on the regulator to allow the voltage to be adjusted from 1-10VDC, so it might even be used to supply 3.3 volts & bypass the fon's first regulator. That would improve the efficiency because a linear, non-switching regulator going from 5V to 3.3 volts is only 3.3/5 = 66% efficient. There's a second linear voltage regulator on the fon that drops 3.3V to 1.9V for the processor (1.9/3.3 = 57% efficient) so maybe even a second one of these switching regulators might be used to advantage. Seems like most of the heat is in that area, so that's probably the bulk of the current draw. Maybe using two of these regulators is overkill, but I'd guess it would improve battery life overall by maybe double. Looking at the size and function of this regulator, I wonder if they are meant to be used in a car USB power adapter (e.g. http://bit.ly/pc9OG). Maybe just cannabalizing one of those things would be cheaper, although it might be fixed at 5V and who knows what efficiency.
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