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+ST232CN w/ capacitors:
+
+5.05v in (from USB via maple), 14.92 out unloaded
+
+with circuit, 14.4v or so. remeasuring later, 13.3-13.7v (with a little can
+capacitor)
+
+
+---------------------------------------------------
+
+Maxim MAX233CPP
+
+Sat Nov 10 21:29:48 CET 2012:
+
+with a 4.7kohm resistor, measure 16.99 volts. noise on output is a combination
+of ~100mV p-p triangle waves at 168 kz, plus extra 120mV p-p bursts at peaks,
+plus random sort-of-digital digressions of about 100mV on a time scale of 5ms
+or so. large amplification of USB input noise? in this configuration, USB
+voltage only wanders by 20mV or so, but maybe current varries.
+
+without any load, output is 19.28v; noise is ~50mV p-p triangle waves with
+100mV peak transients, plus same old macro scale wanderings.
+
+swapping input cap to 0.1uF and adding a 0.1uF output cap gives 40mV total
+noise with transients gone
+
+running entropy.cpp and doing crude stats in python...
+
+no negative resistor, INPUT_PULLDOWN, delay(1):  percent: 26.562500
+no negative resistor, INPUT_PULLDOWN, delay(10): percent: 30.078858
+no negative resistor, INPUT_FLOATING, delay(10): percent: 31.715096
+no negative resistor, INPUT_PULLUP,   delay(10): percent: 32.595183
+
+while probing un-amplified output, percent: 42.660407
+
+switched to a design where the amplifier is fed from the 0/+5v USB power
+instead of -10/+10 output. got:
+
+with negative resistor, INPUT_PULLUP,   delay(10), percent: 50.102838
+with negative resistor, INPUT_PULLUP,   delay(1),  percent: 52.064632
+with negative resistor, INPUT_FLOATING, delay(1),  percent: 48.503847
+with negative resistor, INPUT_PULLDOWN, delay(1),  percent: 45.382451
+
+
+I think that this circuit can not be used for more than about one raw bit per
+milisecond (meaning about 125 bits/second in the end assuming a 1/4 whitening
+and 50% testing redundancy?).
+
+for raw 32 kilobits/sec (eg, like entropykey?) need to sample with a period of
+32 microseconds or so
+