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1076 discussions

LTC4155 design flaw
by Luke Kenneth Casson Leighton 02 Dec '15

02 Dec '15

i've got an enquiry out with Linear, however it looks like there's a serious design flaw with the LTC4155 - not one that's safety-related but one that makes it functionally completely useless. the clue is in looking at page 15 of the datasheet - a diagram which shows the internal operation. in the bottom left corner is a power-selection arrangement, where there are two AND gates. note that they're not symmetrically arranged. the difference between the two is that WALLSNS output is connected to the *input* (inverted) of the USBGT enabler AND gate. what that means is that it is ABSOLUTELY CAST-IRON GUARANTEED - i.e. hard-wired in an inviolate way - that if the 5VDC input is plugged into a wall charger, USB OTG Host Power is ABSOLUTELY 100% WITHOUT FAIL ABSOLUTE guaranteed to be terminated without warning. which: (a) violates the USB-OTG Power Specification (b) is in direct contravention of the statement on page 1 of the LTC4155 datasheet which *clearly* states that the LTC4155 is compliant with USB-OTG Host Power Mode (c) is in clear violation of various laws like "Trade Descriptions Act" of the UK due to the qualifier statement in paragraph 2 which reads "....without needing additional components". all of which is a frickin nuisance, as i now have to go find alternative dual-supply OTG-compliant [boost-mode] battery charger ICs. i've found two already - bq24192i ($7 in low volume and it would require a 2A 5V step-up converter IC as well....], or the MAX77818 which is a 0.4mm pitch BGA - perfect because it even has battery status monitoring built-in, but the 0.4mm pitch BGA _wow_ that's gonna be tough for small china pcb assembly factories to deal with when they're used to QFNs and QFPs. argh! i'll let people know how this goes: i'm expecting to hear from Linear, they *might* confirm that the I2C "REQUEST_OTG" mode does in fact honour the USB OTG Host Power mode properly. if they do, then all is well - otherwise i will need to do a redesign of PCB3. l.

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qualcom snapdragon 410
by Luke Kenneth Casson Leighton 28 Nov '15

28 Nov '15

> [*] https://developer.qualcomm.com/hardware/dragonboard-410c > > ("Free graphics possible" according to the Debian Wiki's ARM 64 port page... > > https://wiki.debian.org/Arm64Port Adreno GPU. niiiice. minimalist hardware datasheet (with pinouts but not mechanical layout) on arrow electronics, as well as a five THOUSAND page datasheet on the hardware registers. this might actually qualify as an FSF-Endorseable processor, and, with a bit of work, might actually be a great candidate for an EOMA68 CPU Card. it will need a MIPI-to-RGB/TTL converter IC on-board. there's I2C, UART, SPI, 2 SDCs (one is eMMC, the other is SD/MMC), only one USB port (bleeeergh!), which means that a USB Hub IC is needed.. so we're looking at... whatever the SoC cost is (knowing qualcomm they'll want around the $12 mark for it), plus USB Hub IC and components ($1.50), plus a MIPI-to-RGB/TTL converter IC (could be as high as $2.50), so we'd be looking at what.... $15.... ... and the allwinner A64 we know is only $5. with 2 USB interfaces, RGB/TTL output.... whyy, god, whyyyyy... :) l.

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laptop power board
by Luke Kenneth Casson Leighton 28 Nov '15

28 Nov '15

.... i have the LTC 4155 15W power IC as well as the STC3115 battery monitor ICs recognised on the I2C bus with 5V power applied, yippeee. embarrassingly, i had the 5V DC socket wired reverse-polarity. this is, uhh, an officially-sanctioned test of the reverse-voltage protection on the power board design. no, really :) on a 2nd (minimally-populated) board i have the 5V regulated output up, but not on the fully-populated board. what i'll do is fill in all the components from the minimally-populated board, testing it as i go along. i'm looking forward to _not_ setting fire to the apartment when i plug in the e-bike lithium battery. unlike many of these "laptop" batteries it has no current protection circuit built-in, and it's perfectly capable of delivering 20 amps maximum current :) l.

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The $5 Raspberry Pi Zero is out
by joem 27 Nov '15

27 Nov '15

The $5 Raspberry Pi is out https://www.raspberrypi.org/blog/raspberry-pi-zero/ All sold out everywhere in hours :(

1 0

laptop main board, power board and ingenic jz4775 cpu card
by Luke Kenneth Casson Leighton 26 Nov '15

26 Nov '15

ok, been quite busy, 3 to 4 different things going on. first one: i've been working on getting the eoma68-a20 board up and running (booting) out of NAND flash, that's been quite hair-raising. using a sunxi 3.15-10-rc5 kernel i was able to use the standard mtd-tools package to erase and write to the hynix TSOP48 NAND chip, placing an SPL-enabled recent version of u-boot onto it. this all worked fine... except it turns out that MLC NAND can self-destruct just by reading! all i can say is, no wonder allwinner's bootloader process is so damn complex! it's like a 4-stage boot: boot0 (minimum bring-up), boot1 (capable of reading NAND as well as SD/MMC FAT partitions), then u-boot (modified to read allwinner's strange partition format) and finally linux kernel. second, the jz4775 CPU Card is finally underway: http://rhombus-tech.net/ingenic/jz4775/news/ this is the first FSF-Endorseable CPU Card, using the 1.2ghz low-power Ingenic MIPS. it seems strange to put a $3 processor alongside $2.50 of NAND Flash and then put in almost $12 of DDR3 RAM ICs (2 GB RAM) but the threshold where SoCs were no longer the most expensive part of a BOM was passed a loong time ago. third, the laptop main board, i've got everything working except the LCD. i've blown up 2 LCDs already, it was necessary to buy 2 more. first mistake was that it was hard to read the datasheet so the connector was reversed: that resulted in -20V being shoved up the backside of the +3.3v sensitive ICs on the LCD, end result when i was finally able to make up a reversed-cable, the "magic smoke" left that LCD. also i hadn't noticed that i'd shorted the 5V rail to the 3.3v rail, which didn't help, and may have damaged some of the GPIOs on one of the EOMA68-A20 boards i have here. still quite a bit to investigate there. fourth, i've managed to smoke about 3-4 Power ICs already - various MOSFETs, two 3 Amp RT8288 PMICs from microdesktop boards i'm using for test purposes - all to get the laptop power / charger board up and running. annoying! but finally a couple of hours ago, by making up a 2nd board with minimal components, i managed to get the LTC4155 up and recognised on the I2C bus, as well as check that it was outputting stable 5V from USB-style input. the next phase is to populate the over-voltage and reverse-voltage protection components. it's getting there... it's just slower than i would like. l.

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laptop power PCB working!
by Luke Kenneth Casson Leighton 26 Nov '15

26 Nov '15

yaaaaa, i have battery-operation, i am currently running an eoma68-a20 off of a 10Ah e-bike battery, and both the LTC4155 charger/dual-supply IC and the ST3115 battery guage IC are up and recogniseable on the I2C bus. i have yet to compile up the linux kernel modules for both these devices, but they are both available... somewhere :) only slight issue to track down: power drops to 4V when the 5V DC is plugged in, i still have to investigate that, but it may be related to the setting of 3A input and i only have a 2A 5V charger. i can change the settings, and i can also "ping" the LTC4155 over the I2C bus... maybe :) but.... progress, yay! l.

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Cool Recycled Laptop Bag for EOMA-68 Laptop?
by Alexander Stephen Thomas Ross 23 Nov '15

23 Nov '15

http://www.protecttheplanet.co.uk/terracycle/denim-messenger-bag.html i look the look of it. made from scrap denim. I’d say looks the part for a laptop bag to sell/go with a eoma-* laptop. I wonder how the sew the scraps together? machine or cheap/slave labour?

3 2

LVDS and HDMI to the same time
by Martin von Kameke 20 Nov '15

20 Nov '15

Hi, It is possible to use lvds and hdmi to the same time? I will display the same picture. Best regards, Martin

2 1

Turris Omnia FLOSS Router
by Alexander Stephen Thomas Ross 16 Nov '15

16 Nov '15

https://omnia.turris.cz/en/ thoughts? there’s one comment on the indiegogo page about the wifi chipsets there looking at using depending on sourcing. not sure that it will be completely free software (inc (ie wifi)firmware & driver). they don’t say what is definition of the "lifetime of the device" is, regarding updates for it? 2 years or 10? ###### I’m looking to get a decent, free software router. come to think of it what about the eome-68 router? When eoma-68 isn’t going to have Ethernet?

3 2

Jetson TX1 Module
by GaCuest 13 Nov '15

13 Nov '15

Maybe this is interesting for EOMA-68... http://www.nvidia.com/object/jetson-tx1-module.html

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