OH, THE HUMANITY I've decided its time to stop throwing random bits of Python at the screen to see what works and write the beginnings of a protocol spec based on what I've done so far....
You in t'office with a bit of spare time tomorrow Chris?
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| Author: | two_OH_five [ Thu Feb 14, 2013 2:49 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
| OH, THE HUMANITY I've decided its time to stop throwing random bits of Python at the screen to see what works and write the beginnings of a protocol spec based on what I've done so far.... You in t'office with a bit of spare time tomorrow Chris? |
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| Author: | Nibbles [ Thu Feb 14, 2013 6:42 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
Off to my favorite site tomorrow Will be in on Saturday all being well, but don't expect much inteligence 
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| Author: | two_OH_five [ Thu Feb 14, 2013 7:55 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
oh ffs After all that, I google CAN temp sensor on the offchance and find there's a whole standard If you've got SAE access (I haven't) have a look at J1939 standard http://zone.ni.com/devzone/cda/epd/p/id/6215 |
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| Author: | Nibbles [ Sat Feb 16, 2013 10:12 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
Circuit design done apart from connector (which I need to choose finally) Struggling to find a connector rated to 20A, but I've stumbled on this which looks interesting. It may also save searching for a box. The only downside is the connector pins are only tin plate not gold so I wouldn't want to see these outside the cabin unless they're in a larger sealed box. http://docs-europe.electrocomponents.co ... d4e8d6.pdf Anyway, progress so far for anyone interested. https://dl.dropbox.com/u/8316230/PDU/PDU_A.pdf |
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| Author: | Nibbles [ Sat Feb 16, 2013 10:30 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
just dropping part numbers for future reference RS. 664-7236 664-7226 664-7267 664-7258 |
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| Author: | Nibbles [ Sun Feb 17, 2013 10:26 am ] |
| Post subject: | Re: Canbus / Power distribution systems |
Been having a rethink. Just goes to show what happens when you let boffins loose on a design and forget about the application, we've ended up with a spec similar to the motec we were slating earlier. the whole concept of canbus / remote switching is lots of small cheap simple modules placed next to the item they're controlling, thus minimizing. Wiring. the other IMPORTANT consideration is making something quick and easy to diagnose and repair by the roadside with no tools or specialist knowledge. So let's say a module goes pop that drives fuel pump, or headlights when It's dark.. easiest to carry a spare module, but then you need a laptop and adapter and knowledge. So, carry a full set of spare modules ready programmed ? Seems ott. I think we need to look at the config for the whole system as a single item, downloadable via the canbus and stored in full in every module. Each module will access only the parts it needs based on its address. This means modules can be swapped for each other or a single spare without a laptop. The only proviso is that the address must be settable by the roadside, either a dipswitch inside or imo in the loom with links on 4 inputs (allows 16 addresses) So. Ditch second chip and dual canbus (since they're not such a problem) go back to 8 in 8 out plus 4 in for address setting. maybe in the future do a high reliability motorsport version with dual can and other similar redundant device / auto switchover features. |
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| Author: | two_OH_five [ Sun Feb 17, 2013 1:01 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
Hmm I think the design you have is OK with twin processors The way I see it the electronics is cheap compared to boxes, connectors etc and the board cost won't differ much. The more cheap io you can pack into the expensive box the better imo - hence it strikes me as a better option to go with the board design you had which is double handy for development The config thing I had an idea about. After yesterdays elm327 discussions how about making a phone/tablet the central monitor? I don't think it's unreasonable to expect that the sort of nerdy person who would deploy a can power distribution grid will have a smartphone If all else fails and you really need the on the fly capability you can buy a cheap tablet and elm device for under a hundred sheets - pretty reasonable and the kids get a new toy when daddy isn't out terrorising the streets Failing that making the network self heal is still only a software problem. For eg Every module on the system backs up the config of the unit before it - 2 has the config for 1, 3 has it for 2 and 1 has it for 3. Say you pull unit 2 and replace with an unassigned one. Unit 3 needs to see unit 2 isn't talking any more and send out the commands to reprogram a blank unit |
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| Author: | Nibbles [ Sun Feb 17, 2013 4:20 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
A few reasons for the decision. 1. Split processor software nightmares. a. Thinking through how the software will work, each chip sees most of the other stuff via it's own canbus (if it works) but can't see it's other half except via I2C. If one canbus fails, we need to pass everything via I2C. The only way I can see it wotking as original concept is to pass ALL canbus traffic via I2C to other processor, in both directions. So, 2x canbus at 250Kbit trying to pass through 1xI2C at 100Kbit. Sausage up an alley but in reverse. b. Setting config & upgrading software. 1xUSB port to PC, 2 chips. Who has control ? Or configure / upgrading via Canbus - has to be done twice, once for each chip. 2. The board is now bigger / more complex than the ECU. Adding the connector exceeeds the pin limit on my version of the CAD system and will require upgrade to the full unlimited version. At the time I bought it, I was evaluating several and it was cheaper to buy the demo & upgrade to full than to buy the full. I always intended to upgrade when needed, but I haven't needed to in 10 years and TBH I think the market is so limited it doesn't justify the money. So - cut it down or shelve it. |
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| Author: | two_OH_five [ Sun Feb 17, 2013 4:53 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
Ah, I was thinking along different lines, initially at least Both connected to the same bus with switchover so basically 1 pdm would appear as two entities on the bus. So everything is identical between software. Additional development could then allow the i2c bus to come into play to combine the 2 units into 1 via internal comms The pin limit is a bit of a domestic pachyderm though Is that down to laying the pdm and dash display on a single board? |
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| Author: | Nibbles [ Sun Feb 17, 2013 8:58 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
All being done on different boards, the manufacturer is combining them for me. |
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| Author: | Nibbles [ Mon Feb 18, 2013 1:12 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
Part numbers for smaller, cheaper version of box & connectors. 664-7220 664-7204 664-7254 664-7267 Thinking of laying out board so all the important connections are on the 30 pin connector so some applications can save a connector. |
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| Author: | two_OH_five [ Tue Feb 19, 2013 12:00 am ] |
| Post subject: | Re: Canbus / Power distribution systems |
Been exercising the old grey matter to produce a cycle accurate version I now have real (virtual) hardware to play with so now have correct timing @250Kb/S CAN speed 16 inputs. Each pin sent with full 16 bit accuracy each packet takes ~500uS 16x = ~8mS as per picture (packets vary a little bit in size due to bitstuffing required in the protocol) It's a bit tight 
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| Author: | two_OH_five [ Tue Feb 19, 2013 11:44 am ] |
| Post subject: | Re: Canbus / Power distribution systems |
Bit of datapath parammeterisation later Now running a max of 8 inputs all with 12 bit resolution. Each PDM now takes ~1.8mS to transmit a complete input compliment I've cut it down so each PDM has a 5mS window allotted and defined a max of 7 PDMs (+ an additional central control unit) on the network. Image shows 7 pdms all talking. Bus utilization is ~35-40% In this configuration response time is 40mS max - almost quick enough to ditch change notification and just rely on periodic status updates 
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| Author: | two_OH_five [ Wed Feb 20, 2013 2:49 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
Random thought of the day And if the boards aren't done and dusted...... If using a single dsPIC you have a free SPI port. SPI powered SDCARD reader modules are cheap enough.... How about storing the configuration on a SDCARD? That way if a PDM fails on the road you can swap it for a blank one simply by swapping SDCARDS This has a couple of benefits - Reduces NV memory requirement You can configure the system offline then just plug the cards into modules It gives you somewhere to log stuff like faults Frees up 4 more inputs to the outside world Downsides You need a card reader + slot in the case somewhere PIC code needs to be able to support SD - a brief search suggests that RAW format isn't difficult Not sure of the size limit but I'd estimate a complete system configuration to be >1KB :- @8 pdm with 8 inputs you have 64 input pins in the system each output needs a "turn on" and a "turn off" flag for every input pin - 128 bits each output needs some config data - flash, flash rate, current limit. Say 32 bits There's 64 output pins in a 8PDM 8 output setup so total is 64*160 bits or ~1300bytes Allow for a few missed things and I reckon 1.5kB of NV memory should be close |
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| Author: | two_OH_five [ Wed Feb 20, 2013 3:00 pm ] |
| Post subject: | Re: Canbus / Power distribution systems |
On a related note  Anyone got an ASIC going spare??
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