CAN BUS ADC Expansion Board

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xgrapher
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CAN BUS ADC Expansion Board

Post by xgrapher »

I'm making my own Arduino based EGT board that will read 6 EGT's and transmit them via CAN to my MS3. What I've understood so far is that I need to Enable ADC POLLING. Define CANID, Table and Offset of the ADC channels and start transmitting them from my microcontroller.

Is my understanding correct?
jsmcortina
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Re: CAN BUS ADC Expansion Board

Post by jsmcortina »

Not quite.

You need to implement the send/receive Megasquirt-CAN protocol. This is documented in the Megasquirt CAN PDF from the Manuals page.

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Alfagta
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Re: CAN BUS ADC Expansion Board

Post by Alfagta »

Hello,

take a look into this. http://www.msextra.com/forums/viewtopic ... 67&t=62735
That board has all you need and all in a solid case.
I don't know how you read the 6 egt sensors with the arduino but when you use
6 time max31855 that's expensive.

Best regards
Alfa 156 GTA
Alfa 75 Race Car MS III -- alway latest FW
Alfa 164 V6 Turbo
Alfa 155 2,5TD RIP
Test MS II --always latest FW
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piledriver
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Re: CAN BUS ADC Expansion Board

Post by piledriver »

The 1wire SPI TC amps actually are ~$4-6.
A 38150K or MAX31855 is pretty cheap by itself, on a custom board.
They only get expensive on the cute little prebuilt breakouts.

MS3 could talk to a string of them directly if the code existed, as it has SPI, only used for knock and clock modules at the moment.
I looked at this but I suck at programming.
Always doing things the hard way, MS2 sequential w/ v1.01 mainboard, LS2 coils. 80 mile/day commuter status.
xgrapher
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Re: CAN BUS ADC Expansion Board

Post by xgrapher »

That's exactly what I am planning to use. I want to daisy chain a bunch of those to my arduino and transmit the data by CAN to MS3. I'm already reading the dash info off the MS3 via CAN
Alfagta
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Re: CAN BUS ADC Expansion Board

Post by Alfagta »

Do you know the samle time for the 1 wire tc amps?
Alfa 156 GTA
Alfa 75 Race Car MS III -- alway latest FW
Alfa 164 V6 Turbo
Alfa 155 2,5TD RIP
Test MS II --always latest FW
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piledriver
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Re: CAN BUS ADC Expansion Board

Post by piledriver »

looks like 1.2 hz at 12 bit, or 10 hz at 9 bit resolution.
Between that and the 700C/1290F temp limit they might be best used for CHT.
(There may be a way to extend the range, but its usually related to power voltage and these run on 3,3v... )

There may exist chips that run on 12v and still talk spi--- Not necessarily 1wire... full spi is capable of much faster transfers than 1 wire IIRC. haven't looked.

The settling time of a typical analog TC amp is ~40us, and the A/D conversion rate is a further variable, but 25-30hz is probably reasonable, double that is usable depending on the A/D setup.
For small changes it is likely faster, and you can of course read it faster, but it may not always tell you much.

You could of course build a very fast TC amp setup plugged into a scope or fast DAQ setup and a fine wire exposed tip EGT probe and see individual cylinders firing at 10K RPM, but not on a MS-anything.

I'd personally love to see MS3 being able to talk to a set of these and a set of 14point7.com WBO2 modules directly over spi and skip the CAN part, as all you'd need is possibly an SPI transciever/buffer if that.

I'm curious what the update rate is of something like a CAN-EGT is for comparison.
Last edited by piledriver on Wed Nov 09, 2016 4:18 am, edited 1 time in total.
Always doing things the hard way, MS2 sequential w/ v1.01 mainboard, LS2 coils. 80 mile/day commuter status.
Alfagta
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Re: CAN BUS ADC Expansion Board

Post by Alfagta »

The MAX31850 has arround 75-100ms sample time according to the data sheet.
Alfa 156 GTA
Alfa 75 Race Car MS III -- alway latest FW
Alfa 164 V6 Turbo
Alfa 155 2,5TD RIP
Test MS II --always latest FW
Tunerstudio V2.6.11 Registered
MegaLog Viewer V3.4.04 Registered
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