Propeller based Mini ITX motherboard
Tubular
Posts: 4,706
This my very rough, first pass at a Propeller based Mini ITX motherboard, that could go in a standard modern PC case.
At its core is a propeller platform variant that includes VGA and AV output via 3.5mm 4 pole phono to 3 x RCA. So we can add expansion shields such as Rayman's DVI shield
In addition there are two identical 4 pin ports, that can be configured as "cheap usb" using resistors and Micah's or BradC's code, or they can accept "proper" modules such as the V2DIP2 from FTDI, which provides a dual USB host. Alternatively the Wiz820io would provide some Ethernet connectivity for about $20. Finally each port can accept a MicroSD or DIP8 chip such as 23K256 SRAM, FLASH, etc
There are 8 I2C sockets at addresses 0-7, and a 16 bit I2C expander since much of the GPIO is taken up by connecting to peripherals.
Haven't worked out what to do with the bottom half just yet. One option is a mirrored design, allowing the board to be cut in half, or used as a dual prop setup. Another option is relays / optocouplers etc, since there is plenty of power available from the ATX power supply
Still lots of layout to do, just exploring at this stage. Any comments welcome.
EDIT: Alternative design using 2 Propeller platforms (1 with external fascia, one internal) and connectors mostly in "normal" position
At its core is a propeller platform variant that includes VGA and AV output via 3.5mm 4 pole phono to 3 x RCA. So we can add expansion shields such as Rayman's DVI shield
In addition there are two identical 4 pin ports, that can be configured as "cheap usb" using resistors and Micah's or BradC's code, or they can accept "proper" modules such as the V2DIP2 from FTDI, which provides a dual USB host. Alternatively the Wiz820io would provide some Ethernet connectivity for about $20. Finally each port can accept a MicroSD or DIP8 chip such as 23K256 SRAM, FLASH, etc
There are 8 I2C sockets at addresses 0-7, and a 16 bit I2C expander since much of the GPIO is taken up by connecting to peripherals.
Haven't worked out what to do with the bottom half just yet. One option is a mirrored design, allowing the board to be cut in half, or used as a dual prop setup. Another option is relays / optocouplers etc, since there is plenty of power available from the ATX power supply
Still lots of layout to do, just exploring at this stage. Any comments welcome.
EDIT: Alternative design using 2 Propeller platforms (1 with external fascia, one internal) and connectors mostly in "normal" position
1024 x 1027 - 138K
1024 x 1036 - 148K
Comments
As for USB, I would suggest using a 2 port stacked USB, next to the PS2 connectors, then break that out to a couple of headers that can be used for Prop or daughter board.
I would also suggest that you decided on an Ethernet controller and just design Ethernet into the board. Since you mention DVI, make the layout so it accommodates Rayman's plugin board above the VGA connector.
References:
http://en.wikipedia.org/wiki/ATX
http://www.tyan.com/archive/support/html/io_shield.html
http://www.formfactors.org/developer\specs\atx2_2.pdf
Have a look, especially at the I/O section of the ATX spec, for a good example layout.
I would recommend searching google for "atx i/o plate" and finding an I/O plate that can be purchased individually, then matching that layout.
Also, your layout doesn't look right, Mini-ITX is 170mm square, has an ATX screw pattern, and the board extends into the first slot area. Your board appears to only cover the back panel area.
I might suggest adding some SPI ram and flash on the board, for XMM memory model code. A full size SD card socket, DIL expansion header (perhaps in addition to the PP pins, or other, matching the Quickstart header).
A secondary Prop for expanded I/O, plus at least 2 16 bit I2C I/O expanders. I would drive both props from a single can oscillator, instead of a crystal, for stability and phase sync. If you do that, you can do high speed
prop 2 prop comms with complete phase accuracy and not need a clock signal. Just sync with a WAITPEQ, then just write and read, they both will be in sync and not need a clock pulse.
The small RAM within the Prop1 is really going to be a limiting factor in this sort of design.
The P2 will have external SDRAM, SPI boot flash, and a boat load of I/O. Certainly USB would be bit-banged, ethernet is even possible.
The Video I/O circuitry is completely different since the P2 has on-chip DACs, and you could do DVI out with the TFP chip Rayman is using.
I think it best to stick to a P1 layout for now, and conjure up a P2 later.
How did you figure out the mounting hole spacing? I'm wondering how small a board can fit in there... ExpressPCB limits me to 21 square inches for prototype boards...
Prop2 will eliminate the need for a lot of the extra components that Prop1 needs... But, until then...
I think I would use a VNC2 64-pin chip to do the USB... It could also do the LAN via wiznet chip and audio via VLSI chip...
P2 would be a much better choice, but for what I want to do P1 will be just fine. We also need to work out an agreed upon form factor or platform for P2 expansion shields, and its too early to do that.
I want to support Rayman's DVI shield, and that necessitates a custom i/o plate. Since I'm already departing slightly from the norm there is no issue with arranging the connectors in a non standard order. That nice spec document pedward links to advises "To retain maximum flexibility, the exact positioning of connectors within the I/O connector zone is left to the discretion of the motherboard designer.", and it's the motherboards that come with their matching shield plates. So I'll just get something lasercut.
I thought about putting a whole heap of RAM chips down, but decided it would be better to do this via the propeller platform expansion. Someone may well have already done it. However I may look at modifying the 8 I2C sockets so they could also take SPI chips, by using an I2C expander to drive the chip select lines, but still have pullup/pulldown resistors on each pin 1 or 2 to set default addresses in case that feature is not required.
Mini ITX does nest into the "back panel area" and only uses the 4 corner screws (C F H J in your linked spec). Mini ITX only supports /extends into the one PCI slot area. The middle screws relate to neo ITX if it takes off, or provide additional mounting in case the board is cut in half.
The stacked USB dualled with the PS2 is a good idea. There are 10 pin headers over on the right side to connect to the 2 or 4 USB connectors on the front panel of the computer case.
The common clock is also a good idea if I mirror the same for the bottom section. Full size SD may be doable if I can find one that nests close to the board edge, because there are other holes from the stacked USB connector that can't move. I have seen some SD connectors that are "half depth" that may work, lets see.
thanks again
tubular
The 40-pin connector in the middle of the DVI shield provides the input. Or, I'm about to sell a small VGA plugin board for the DVI shield.
With that board installed, you can get VGA from the DVI connector using those DVI to VGA adapters you get with modern video cards....
I guess it doesn't really need the panel. I've had a computer that went without before...
I would use a stacked USB-A connector instead of stacked PS2 because a lot of the USB keyboards are PS2 compatible anyways. You can buy PS2 to USB adapters cheaply. I am not sure whether the USB mouse these days are also PS2 compatible - anywone know this???
I dont think the rear layout matters much. A laser cut plate or a pcb routed plate would work fine. In fact, we dont even need a plate for hobbyists. The main fact is that we have a case to put our project in.
That might make more sense actually (M350 Universal Mini-ITX PC enclosure) since I don't think we really need a lot of power...
Did actually have a similar concept in mind (PropBox2) using a Hammond enclosure.
But, this idea might have a lot of advantages...
Yes there are 2 options for the USB. Either the cheap, 4 resistors per port method (BradC, Micah, M K Borri's ADB etc) with twin USB-A stacked connector, or you can plug in a $22 V2DIP2 (which has a Vinculum VNC2 and 2 USB A ports onboard). Depends on how much 'compliance' you want.
For the ethernet, I'm going with a Wiz820io which is about $20 from Wiznet.
I went to the local computer shop just to investigate pricing on cases, PSUs etc. It had been a few years between visits. I was stunned that a nice looking case with 500w PSU, and metal edges that don't slice off digits, was only $45. So I just bought it on the spot, and here we are. The goal is just to work with the standard connectors the case comes with, hence the ATX 24 pin power header, and option to connect to front panel USB ports, speaker, reset switch etc
I have a mini ITX motherboard from Intel that I am basing off. Its either an Intel D525MW or D410PT. Cost me $80 or so, Frys used to sell them, I notice they now have a $90 Via mini itx motherboard. Mounting hole spacing is in the intel manual, but is just a subset of the original ATX spec.
Here's a couple of links to Intel / Via mini itx products
http://www.intel.com/content/www/us/en/desktops/desktop-board-d525mw-interactive-layout-demo-video.html
http://www.via.com.tw/en/products/viamainboards/ve900/index.jsp
I understand it would be nice to have something that exactly matched commercial motherboards, but I'm unsure whether there is a major benefit here? The two SPI 'ports' that can have twin USB-A or Ethernet or SD card require their own kind of cutout, because the V2DIP2 or Wiz820io modules will offset vertically (lift) the connectors off the motherboard. And Rayman's DVI shield will probably have the DVI connector at a different position to all the commercial boards.
The lasercut custom shield will cost nothing much to make in any quantity from 10 to 1000, and take me less time than sourcing anything in bulk from overseas.
When we do a P2 variant it might be different, because the applications run may be a lot more potent, and that in turn justifies plonking down surface mount ethernet chipsets and flush connectors etc, rather than the 'module or cheap connector' approach I've employed here.
I would be a little cautious with a 500W supply - many switch-mode power supplies have minimum load needs to give half reasonable regulation.
Yes that is good advice. I won't be using the 3v3 rail from the PSU but probably the 5v with a LDO TO-220 reg. There is the option of using a TO-220 switcher module in the same space to go down from 12v if need be, but that probably has even worse regulation.
I do note the 3v3 rail from the PSU sometimes has a sense wire.
Many products have PS/2 support "idling in the corner", as once they have it, it costs almost nothing to keep it.
You can get cheap adapters going both ways, so I do not have a problem with Stacked PS/2.
I think it is good to be visually clear on what the hardware supports, so a USB socket that expected PS/2 only, would not be a good idea.
Thus I'd prefer 2 x PS/2 and also 2 x USB using the VINC2 - that's quite a cheap way to get Dual USB, and 256K of flash.
A prop alone is going to get over-whelmed, so careful choice of 'helpers' will be important.
Mapping to all 6 pins on a PS/2 plug, would also allow easy firmware support of PS/2, i2c, or SPI expansion, all on the same simple connector.
Even Dual i2c would be workable, which could support a mix of i2c (std Bidirectional) to FM+ and then another SCL/SDA pair, that supported the new UFm unidirectional speed.
I would suggest having the PS2 and Mouse in the "normal" spot that EVERY motherboard (other than the Intel marlin) has it, just for consistency. Then, next to that I would suggest the standard dual USB, terminated for onboard use via bit-bang. I would then put an outline for the VNC2 on the other end of the back panel. You have a reasonable assumption of the dimensions for that, so plan for that part. Next, include just a 3 stack audio/video connector suite. At least 1 for stereo audio, the other 2 could be stubbed out. If you can find a unit that has 2 sub-jacks and 1 RCA jack, you could put NTSC on the RCA jack. The second sub-mini jack could be for input, but stubbed to a header location.
I would then layout an on-board ethernet. There are 2 choices, the wiznet chip, which has the TCP stack in it, but only supports 4 connection slots, or the MicroChip ENC28J60, which provides a MAC interface and allows the propeller to do the TCP/IP. IIRC there is an object in OBEX to talk to this chip. After playing with the wiznet chip, I would like the flexibility the ENC offers. After all, when it's just software, you can do a lot with a little. When you are tied down by the manufacturer's firmware, you are limited in what you can accomplish. I'm not talking about 50,000 simultaneous connections, but I'm talking about having the ability to prevent SUPER-EASY DoS attacks against embedded hardware. Since the WIZ only allows 4 connections, you can DoS it trivially easy with something like a smartphone.
For Rayman's contribution, perhaps you should consider laying out part of the board with his design, collaborate, instead of using a daughter card? The other choice is to do a layout that takes his geometry as the primary consideration, then place everything else around it.
Also, the 24 pin ATX connector isn't too widely offered, the original 20 pin variety is much more common, with the auxiliary 4 pin connector taking the place of the extended 24pin connector. The connector series is Molex Mini-fit Jr, I have a few sitting around from a previous project.
I would encourage you to resize the board to the full 170mm and utilize as much of the real estate as you can. Also, definitely use the 3.3v supply, what's the point of having a multi-voltage supply and then putting linear regulators on the board?
If you can find room, perhaps the SD connector should protrude through the back panel, for ease of access. Then again, if this design actually gets used for a PoS or other dumb terminal, having the SD card locked inside would be a good thing. The VNC chip will handle USB FOB drives anyway, so you have external access.
The more I think about it, you are really looking towards a dual prop design to get enough I/O and COGs to handle the peripherals.
Yes, it's silly to pile all this stuff on, but just attempting a Mini-ITX board is a silly endeavor to begin with! (I'm right beside you, thinking it's a cool idea for hack value alone).
Oh, forgot, put a legitimate RS-232 9pin port on it, with a MAX232 driver. This board could be a great reference platform to build a bunch of different dedicated use devices from, especially since it leverages a whole suite of standard hardware. I can think of 1 use that people would love it for: CNC machine download/DNC in the shop. A no-moving-part network accessible, dumb machine that any operator could use. Shops are nasty places, with dust, coolant film, and little bits of swarf flying about (it gets in EVERYWHERE).
I'm located in Australia. I visit the US every year or two, will be over there again in Oct / Nov.
Thanks for your feedback. I haven't built many desktop PCs in recent years. It probably makes sense to change over to 20 pin molex.
And as for the 9 pin D connector, I have ordered a bunch of Kycon stacking connectors, I think one has a 15 pin VGA + 9 pin D, which might work nicely. I also ordered some of the RCA stackers but these only had 2 RCA (red and white) for audio applications. There may be some better stacks out there.
I am toying with the idea of just having two propeller platforms side by side, and doing the "variants" using the shield stack. That enables us to go easily with different ethernet chipsets, and cheap or expensive solutions just by choosing the correct shield. The base PCB could probably be single sided. The shields probably won't do double stacked USB A's, but it is more flexible, plus any shields created can be used with other propeller platforms. It may be possible to get up to 2 shields on top of the base, will check out later exactly how much vertical space we have available.
I actually forgot there are footprints under the DIP prop for C3 style memory, so if loaded and pins p8~11 and 25 are available each prop has 64k SRAM, a flash chip, 2ch ADC and internal micro SD (on p0~3).
Will post a rough sketch later
Such 'stacks' sound a good idea.
There seem to be some quite compact ITC cases, such as this one
http://www.logicsupply.com/products/t_3310
or this, for a non PSU variant
http://www.logicsupply.com/products/m350
Yeah looking into it there are quite a few nice cases for mini-itx (mitx as it seems to be referred as sometimes)
This one too
http://www.apextechusa.com/products.asp?pID=115
Amazon actually has a nice cross section which is where I found that one. Some of them are quite stylish.
And I guess we don't strictly need a several hundred watt power supply - the usual wall wart could be used.
There was an outfit that built rackmount Mini-ITX machines for servers, like internet radio stations. They designed a DC-DC converter power supply and compact flash-to-IDE plugin board. Unfortunately the connector layout changed between the first and second gen VIA board and the CF adapter didn't work. The company was called ituner networks.
EDIT: Check this out: http://www.mini-box.com/s.nl/it.A/id.417/.f?sc=8&category=13
That's cute.
Just need to figure what tasks can use the spare 119 watts... ?
I have one of those power inverter modules for driving my Intel mini-itx board off a solar charged gel cel. They were quite cheap and seem to do the job just fine.
Christmas lighting... RGB led strips, servo motors etc
The main advantage is the connectors are in more "normal" positioning. There is room for a serial D9 but only if the 3x3.5mm audio stack is sacrificed. Since there is a 4 pole "tv out" that includes stereo audio I don't see this as a big sacrifice - we effectively lose microphone/audio input, and it could always be added via PP expansion anyways.
I think there would be room for a full sized SD slot under the V2DIP2, but until the module turns up it's hard to tell exactly.
The big space down the bottom could be used for many things. A full sized breadboard is actually a reasonable fit (could have a large proto area with the copper tracks laid out, or could stick a breadboard over the same area). Just one idea.
More efficient, certainly. But we have plenty of space compared to what we're used to. I'm focused on PP's because I want to make some shields to do custom tricks. And those shields can be used with any of the 5 or 6 PP based designs on the Smorgasboard too, or Martin's new variant(s) of the PP.
The ability to use Rayman's DVI is a good example of just being able to grab an off the shelf shield and gain special powers. Lets face it there is a ridiculous amount of space compared to what we're used to.
Yeah that could work too.
Lots of embedded PCs have a "cable kit" that comes with VGA, COM, USB, PIDE pins etc. Most connectors are 2mm pitch rather than 0.1". We pay $25 for the cable kits, I'm sure you could find similar on ebay much cheaper.
So you'd just need to design a PP shield with a heap of 2mm headers on it, and perhaps Vinculum 2 and/or ENC28J60 if required.
My suggestion is to do a dual prop, 1 of the props would have a PPUSB layout, both could have a 40 pin header, like the quickstart, for I/O pin access.
I would also recommend using the QFP for layout instead of the DIP40, you are already picking other packages that are SMT (wiznet), so you might as well go all out.