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Diffstat (limited to 'ps_notes')
| -rw-r--r-- | ps_notes | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/ps_notes b/ps_notes new file mode 100644 index 0000000..349ac11 --- /dev/null +++ b/ps_notes @@ -0,0 +1,52 @@ + +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 + |