arm-netbook

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ecocomputing white paper
by Luke Kenneth Casson Leighton 08 Sep '15

08 Sep '15

http://rhombus-tech.net/whitepapers/ecocomputing_07sep2015/ anyone on the IRC channel may have noticed the flood of git commits as i made several successive minor changes and used "git commit" to upload them for proper reading in-place. basically this was written based on the conversations, questions and challenges that people here on arm-netbooks have raised over the years since the list was started, so i particularly wanted to say thank you to all of you for indirectly helping in that way and making it possible to write this white paper in one day. i've been planning it for some time, but there wasn't quite a right time. l.

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libre 15in laptop progress: pcbs and parts
by Luke Kenneth Casson Leighton 05 Sep '15

05 Sep '15

okaaaay sooo, whew :) spent the entire day online looking up digikey part numbers... eyes are going funny (square _and_ crossed....) but i got there. 65 items from digikey, then another 5 or so that need to be sourced from china (only) - a special narrow 3.5mm jack which can re-route both outputs to speakers if the headphone jack's not plugged in, a CM108AH USB Audio IC, GL850G hub, SY6280 USB power control IC and a SY7201 step-up converter for the 3.5 watt LCD backlight. they're all easy to get... just not outside of china. i also ordered qty2 of the PCB1 (main laptop interface board) and PCB2 (embedded controller, keyboard/mouse) as "bare prototype" boards, 0.5oz copper, from eurocircuits. the 4 boards came to a total of $EUR 100, which is pretty amazing for europe, and they were very tolerant about me making a mistake and having to cancel the order, make some changes, and re-submit even after i'd actually paid (they don't normally allow that!). i did have to redesign all the PCBs to use a 24mil surround around the 10mil drill holes - and change all the track-to-track min clearance to 7mil and the min track width to 8mil. this was the *absolute* minimum that eurocircuits "prototype pool" would allow. *sigh* i'm also going to have to go back and adjust the casework to cope with a 1.6mm PCB thickness.... i'd designed it for 1.2mm and yes, really, 0.4mm makes a huge difference, it will be about a day's work to adjust all the 3D parts. the power board (PCB3).... yyyeah i am having fun, there. the example board layout i got from linear tech's online resources says that 2oz copper is needed. *nobody* does 2oz copper with anything below 12mil track and 12mil track-to-track.... yet the distance between the pads on an LTC4155 are 7.8mil (0.2mm)... what's up with that?? soo... hmmm, i'm looking up current handling calculators online to see if i can get away with 1oz copper.... and i believe i can. which would be good, if it was the case, as i can go to eurocircuits.... BUT, i would have to make a "standard" order not prototype because the proto boards are only available in 0.5oz copper... oh! and the 1kW IR solder station arrived. it's.... much more basic than i was expecting :) there are two thermistors that you're supposed to like stick somewhere around the PCB when the 800W pre-heater and the 200W IR lamp are on.... .... i got them in the wrong place on the first board i tried (a 1in prototype board) and was fascinated to see it sizzle within about 15 seconds, this little black spot about 8mm in diameter appeared and i spent the rest of the day with the smell of cooked fibreglass up my nose... mmmm looovely :) anyway it appears that it actually works, must get some solder paste, start doing some desoldering of components on random boards as an experiment, it'll be fuuuun.... l.

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EOMA68 interface update proposal: -GbE, +USB3.1, +GPIO
by Luke Kenneth Casson Leighton 03 Sep '15

03 Sep '15

ok, soo... i've been following the updates to USB3 (10 gigabit speeds now with USB 3.1). in combination with: * the development of both the tablet and the laptop not having room for an ethernet port * the development of lower-cost SoCs not really having ethernet * the fact that the ethernet components cost around $2 when the SoCs themselves are around $2 to $4 ... i'm coming to the conclusion that Ethernet should be removed, and the 9 lines used to * increase the USB3.0 allocation (4 wires) to USB 3.1 (8 wires) * this would leave 5 spare pins for GPIO. * at least two of those should be EINT-capable GPIOs this would make it possible to redesign the tablet PCB to a more "standard" one - removing the need for the I2C GPIO chip for example. if there are any products that need ethernet, it can be done as a USB2 or USB3 compliant external IC. the IC3128 PCB can be reduced down to around a $12 BOM, the EOMA68-A20 PCB can be reduced by a further $2.50. any thoughts or objections, much appreciated the input. l.

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libre laptop 1st and 2nd pcbs off to eurocircuits
by Luke Kenneth Casson Leighton 02 Sep '15

02 Sep '15

ok so i chose the "prototype" option - no solder mask, no silkscreen, just bare copper. the rules for the eurocircuits proto boards are... both strict and also odd. there's a minimum via size which is quite huge (24mil surround, 10mil drill), fortunately however i've been able to design all 3 pcbs around that. i believe it means that there is a big advantage when it comes to production: lower cost! :) also the 1kW IR soldering station is arriving tomorrow, it will be.... interesting to work out how to use it. i will try some experiments first... l.

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libre laptop pcbs
by Luke Kenneth Casson Leighton 28 Aug '15

28 Aug '15

ok, sooo, i'm nearly ready to begin ordering components, and i found that eurocircuits do an amazingly cheap deal with a fast turnaround on 2-layer 1.6mm FR4 prototype boards (no masks or silkscreen). on the charger IC board i've had to replace one of the power MOSFETs already, the one that is in the recommended circuit from linear tech has gone EOL! so many small details to sort out it's amazing... l.

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help needed with a ttl logic circuit
by Luke Kenneth Casson Leighton 25 Aug '15

25 Aug '15

hi folks could someone please help analyse this circuit to see if it is correct? http://hands.com/~lkcl/ttl_logic_circuit.png the requirement: * an STM32F's "BOOT0" is, by default "pulled to GND" in order that "normal" operation happens * the boot operation needs to be selectable by a GPIO from a main CPU (TTL, with a different voltage) * if however the main CPU's GPIO is *DISCONNECTED*, "normal" operation of the STM32F is required. so, the main things here are: * the STM32F is run from a 3.3v supply * the CPU can be a totally different TTL voltage level from the STM32F. it could be 5.0V, it could be 3.3v, it could be 3.0v, it could be even 1.8v. * the default behaviour needs to be "pull to GND", even if the input is floating. R28 ensures that the transistor is, by default, ON, so that R2 is connected to GND and thus BOOT0 operates in "normal" mode. however current will flow from EXT_BOOT0 if it is "high", which would start fighting with VCC_SYS_3V3 if EXT_BOOT0 is over 3.3v, so D1 stops that from happening. i think i'm stuck though when it comes to pulling EXT_BOOT0 down to "GND" because actually it will be TTL 0.7v (or so), which, when the diode is taken into account (another 0.7v), i don't think it's enough to switch off the transistor. ... so.... help! what do i do? tia, l.

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libre 15in laptop PCB progress
by Luke Kenneth Casson Leighton 20 Aug '15

20 Aug '15

http://rhombus-tech.net/community_ideas/laptop_15in/news/ so i made some screen-shots and annotated them - the PCB designs are almost done already! i am thinking of doing the assembly myself, because they are only single-side components. if anyone has any suggestions on a low-cost IRDA BGA / SMD station (i see there is something called a T862 on ebay and amazon), i would appreciate the advice as i am going to go ahead fairly soon. what i am first going to do is get the PCBs made up (they're like $50 not $500!) and, before assembly, check that they're all the right size, that the parts are likely to go in the right places. then, because i will have the actual PCBs like in my hands this time, it makes sense to do the assembly myself as well. i want to do this in order to demonstrate to people that even someone like me who has "basic" skill in soldering can actually consider making a complex thing like a laptop by using ready-made EOMA68 compliant CPU Cards.... and that it really should not cost a fortune to do so, either. that's really what this whole thing is about. previously though i was doing 4 layer board designs ($500 for qty 5 prototype PCBs) so that possibility really wasn't clear. ... now it is. l.

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15in libre hardware laptop PCB progress
by Luke Kenneth Casson Leighton 16 Aug '15

16 Aug '15

ok, so i started last week on the PCBs. first thing: there's three of them. the casework, needing to have a middle strut as well as other internal supports, makes it impossible to have a single PCB, apart from anything that PCB would be just over 12in wide. also things need to be on different levels. so the PCBs are divided as follows: * PCB1 - contains the CPU card, I/O connectors, LVDS converter IC, USB Audio IC, USB Hub, EOMA68 identifier EEPROM, and some ribbon connectors * PCB2 - contains an STM32F070 and 3 FPCs: one for the touchpanel LCD (which has an SPI converter IC on it), one for the capacitive touchpanel (I2C), and one 16+8 1mm pitch connector for the keyboard. * PCB3 - contains the battery charger and power IC (an LTC4155) as well as a battery monitor IC (STC3115) which measures current as well as voltage. the LTC4155 is absolutely awesome, it has dual supply inputs (5V in and USB-OTG), it can be turned round to *supply* 5V USB-OTG, *and* it can provide up to 3A @ 5V as system output. all three PCBs will be double-sided 2 layer, with components only on one side. cheap and cheerful. PCB3 will need to be 2oz copper because it's dealing with 4 to 5 amps in places. PCB1 is deliberately huge so that i have plenty of space to work with. i have had to do a little bit of rearranging so that there are less wires crossing over - for example, the MicroSD and the USB (CM108AH) Headphone jack have now swapped places. as a result, the micro-sd wires can run directly on the TOP layer - without crossing anything (especially USB traces). previously, the MicroSD lines would have had to cross over the USB audio lines. in a 4 layer PCB that's fine, because they're separated by an entire GND plane. in a 2 layer board? mmmm.... no :) so, now, the USB Hub is in the bottom left corner, the USB differential pairs go directly to the connectors (and to the USB Audio IC) - no crossing over... nothing. the SN75LVDS83b (LVDS converter IC) is... distinctly odd. it's extremely puzzlingly well designed. by placing it right next to the EOMA68 connector the 24-pin RGB/TTL outputs can be kept extremely short, with virtually no traces needing to cross over. even the LVDS differential pair outputs do not need to cross over to other layers: they may go directly to the LCD connector. PCB2 is the weird one: it's relatively large (3in x 5in L-shaped) but has an extremely low component count. i tried to use a 48-pin STM32F070, got even the PCB layout done, and realised that it just wasn't going to work: the multiplexing is just too tight, what with 24 of the pins used up for the 8x16 keyboard matrix. 4 more are needed for SPI, 2 for I2C, 5 more for GPIO, 2 for USB. btw - jaezzuss, last night it took 2 hours to go through all the connections of the keyboard with a multimeter, but it had to be done :) i needed to know the layout of the pinouts, and after experimenting pressing random keys i realised, with deep foreboding, that i *literally* had to go through absolutely every single key in turn, starting with ESC and ending at ENTER, putting a heavy object on every key and then manually scanning with a multimeter *all* 24 pins and recording the result. it turns out that yes it's a 16x8 layout. 8 bits vertical, 16 bits horizontal. there was very little pattern to the layout. a little bit of a pattern with the QWERTY keys and the numpad, but everything else pretty much completely defied logic! the idea here with the STM32F070 (which is very low cost btw) is that it will act as a USB-HID device. so, it will be necessary to provide power down one bank of 8 GPIOs, and to read 2 bytes of output from 16 GPIOs... that way you identify which keys are held down. the reason why i will have to go to the 64-pin QFP is because i don't want to use pins A0-A7 then B0-B4, C2-C3, then back to bank B for a bit.... i want to just use A0-A7, B0-B7, C0-C7 or whatever it takes, so that i can keep things very very simple: read one byte (register A), write one byte (register B) and so on. i haven't yet thought about what kind of interface to offer, when controlling the backlit 480x320 LCD, but that need not be of immediate concern. there is plenty of static RAM on-board the STM32F070 to make an on-board framebuffer. converting to USB-TTY (ACM) so that commands can be sent over a USB-serial port... this would tend to be the simplest way... it can all be taken care of later. btw, word of warning (to anyone else designing a laptop) - i've had to shuffle things around somewhat, significantly, based on what connectors could be obtained today (at reasonable prices). for example, FPC 24 pin 1mm "TOP Connect" wasn't available, so i had to use "Bottom Connect", which meant folding the keyboard's thin-film circuit connector into an S-Shape in order to fit it within the available space. this was to make sure that the connector could remain on the same side as all the other components on PCB2, otherwise it is more expensive to lay out the components on the PCB (you can't use solder reflow). you just can't predict absolutely everything - you can't expect absolutely everything to be available. sometimes you just have to adjust and work round problems. l.

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Vero Apparatus: Another Arm Laptop Project
by Alexander Stephen Thomas Ross 13 Aug '15

13 Aug '15

http://wiki.vero-apparatus.com/ leant of it via #neo900 on freenode thanks to edwin.

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15.6in libre-hardware laptop prototype casework fully assembled
by Luke Kenneth Casson Leighton 07 Aug '15

07 Aug '15

http://rhombus-tech.net/community_ideas/laptop_15in/news/ ok, i'm done with major/minor details of the plastic, got something that "does the job", may need minor tweaking but for now it's done. woo! i'll celebrate tomorrow evening, i have a tennis match in the afternoon. next is to do the PCBs, whilst on the back burner sort out tape and a bezel for the LCD (and touchpanel), etc. etc. l.

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