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authorDaniel Silverstone <dsilvers@digital-scurf.org>2019-04-13 13:24:53 +0100
committerDaniel Silverstone <dsilvers@digital-scurf.org>2019-04-13 13:24:53 +0100
commit75eec03d3b1918afb98fcdd65181ff4659c26bc9 (patch)
tree782870704cffb170b47368c288d527ff734ca0be /parts
parent27cde35bbe3fa5260e01cacac622ce6c571758c9 (diff)
downloadentropykey-75eec03d3b1918afb98fcdd65181ff4659c26bc9.tar.bz2
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+Parts Selection
+===============
+
+Where possible, we're selecting parts purchasable from LCSC because that way
+we can combine shipping from JLCPCB when we order the prototypes...
+
+Prices, where stated, are correct as of Saturday April 13th 2019
+
+Pricing calculated based on the idea of ordering enough parts to build five
+so slop components up to ten, though perhaps not for the CPUs.
+
+Large ICs
+---------
+
+### Processor
+
+Processor will be an STM32F103C (LQFP48) and the options are:
+
+C8303 - C6 part, 32K flash - £1.66 in ones, £11.63 for 7
+C9861 - C8 part, 64K flash - £2.02 in ones, £14.17 for 7
+C8304 - CB part, 128K flash - £2.05 in ones, £14.32 for 7
+
+For prototypes, we're going with C8304 for the easiest time of things.
+Production may drop to C8303 if we can make the firmware small enough.
+
+### Hex inverter
+
+We used an AHCU part in the original ekey, and an ALS in the original
+prototype. We're trying an HCU part for this variant.
+
+C129521 - Hex inverter - £0.084 in tens, £0.84 for 10
+
+https://datasheet.lcsc.com/szlcsc/NXP-Semicon-74HCU04PW_C129521.pdf
+
+Power supplies
+--------------
+
+### 3.3v supply
+
+We don't need a huge amount of power here, so 150mA or so of LDO should
+be plenty, let's get the most efficient we can though.
+
+C83932 - 3v3 250mA - £0.0171 in 20s, £0.342 for 20 - MOQ
+
+### HV DC-DC
+
+C181783 - MT3540-F23 - £0.0511 in fives - £0.511 for 10
+
+https://datasheet.lcsc.com/szlcsc/XI-AN-Aerosemi-Tech-MT3540-F23_C181783.pdf
+
+The -F23 has a 1.23v reference so a 150k/10k divider ought to give us approx.
+20 volts on the HV line.
+
+### Inductor for HV DC-DC
+
+We need a wire-wound inductor with shielding.
+
+C218837 - 10uH 3x3x1.2 inductor - £0.0888 in 10s - £0.888 for 10
+
+https://datasheet.lcsc.com/szlcsc/Cyntec-PST031B-100MS_C218837.pdf
+
+Noise Generators
+----------------
+
+Noise generation needs moderately high hFE transistors. We used BC817-25-N
+in the original ekey (though I think I used random NPN things when I built the
+prototype. We need four per noise generator, so 40 for building 10 units.
+
+C181168 - SOT-23-3 BEC layout - 0.0046 in 50s - £0.23 for 50
+
+Misc parts
+----------
+
+### USB protection chip
+
+While this isn't large, it's also not generic cress, so… we need a USBUF01W6
+to protect a device. This also includes the presence pullup so we're able
+to save space by not needing additional transistors and resistors.
+
+C123726 - USBUF01W6 - £0.3664 in 10s, £3.664 for 10
+
+### Crystal
+
+Driving the STM32 HSE can be done with anything from 8 to 16 MHz. To be
+effective we need it to be able to generate the 48MHz USB clock which means
+we want 8 or 12 really. 8 is most common on developer boards, so let's stick
+with that…
+
+C133333 - SMD-5032_4P - £0.1314 in 10s, £1.314 for 10
+XTAL across pins 1 and 3
+
+https://datasheet.lcsc.com/szlcsc/Zhejiang-Abel-Elec-SMD-5032-4P8M20pf20ppm_C133333.pdf
+
+### USB plug/socket
+
+For the production units we'll need an A-plug, but for prototype development
+we'll fit B-sockets of some kind. Full-on chunky B connectors will be very
+physically stable which is good for a prototype.
+
+C46392 - B socket - £0.0591 in 5s - £0.591 for 10
+
+https://datasheet.lcsc.com/szlcsc/Jing-Extension-of-the-Electronic-Co-LCSC-USB-BFemale90Degree-of-iron-feet-White-plastic-Not-high-temperature_C46392.pdf
+
+### LED(s)
+
+For the prototype we should fit a bunch'o'LEDs so that we can develop usefully
+when debugging gets tough.
+
+C205445 - Orange-red 0603 - £0.0044 in 50s - £0.22 for 50
+
+C205450 - Green-Yellow 0603 - £0.0049 in 50s - £0.245 for 50
+
+C193191 - Blue 0603 - £0.0049 in 50s - £0.245 for 50
+
+Probably fit one of each to each board for convenience.
+