Canbus a82C250

Hi. I am trying to access data on a existing canbus that uses the a82c250 chip. The project in question is a R.O.V. The data that is transmitted to the topside control box is displayed on a small graphic LCD. That's small and Not visible in daylight. The markings on the LCD are Sg12864aslb-hs-2 This looks to be a 128X64. The canbus speed is 138.24 kbs. When I get the data from the canbus I will use a OSD to display it on the main viewing monitor. The other method I was looking at is to read the LCD data lines and access the data that way.

Any advice on the subject would be most welcome.

Regards Antony

Hi. Still no further on on this... Realy struggling and going in circles.

Is there any advice out there ???

Regards Antony

Are you using a CANBUS Shield? Which one?

When I get the data from the canbus I will use a OSD to display it on the main viewing monitor.

The goal is to get the data into a PC?

Hi?
Not yet got a shield or another can device as I don’t want to splash out on something that’s of no use to me for the project…
I would like advice in hardware requires as well as methods.
This is the one I was looking @.
http://www.hobbytronics.co.uk/can-bus-shield

I found a link that describes the videoray can bus.
http://ntnu.diva-portal.org/smash/get/diva2:360686/FULLTEXT01
It starts on page 119.

The data will be put into the video line and be displayed on the main ROV display viewing panel.

Regards Antony

The Communication Protocol for VideoRay Pro III and Desktop Computer Physical media: RS232, baud rate 9600, 8 bit, 1 stop, no parity.

The document is describing an RS-232 serial port. Where does CANBUS come into play?

The canbus speed is 138.24 kbs.

Are you certain that is the bitrate?

Hi I think they are talking about the data after its been decoded...?? There is another document that shows this better. http://bib.irb.hr/datoteka/306954.paper_CAMS07_final.pdf This shows a 232can dongle. What I need to know is..If I tap into the can low and can high plus the ground will I be able to read the data ??. Regards Antony

What I need to know is..If I tap into the can low and can high plus the ground will I be able to read the data ??.

I can think of two potential problems...

If I remember correctly, the length of a "tap" is limited to 1 meter.

That odd bitrate (138.24kbit/s). You need to make certain the CANBUS controller you plan to use supports that bitrate.

Hi. Thanks for the reply.

The Tap length distance will be less than 200mm. So no worries in that area.

As far as the hardware is concerned will the board below do what I want and access the 138.24kbs.?? http://www.hobbytronics.co.uk/can-bus-shield

Reading the data sheets for the chips on the board MCP2515 and the MCP2551. I should be able to read that speed with no problembs. Can anyone confirm this for me??.

Regards Antony

This will help... http://ww1.microchip.com/downloads/en/AppNotes/00754.pdf

And you need to know the MCP2515 oscillator frequency. It's given on the schematic as 16 MHz.

Hi.

Thanks for that link Coding.. Hard reading but informative. Also found a link to a Canbus calculator http://intrepidcs.com/support/mbtime.htm

I have orders the above Shield. Just waiting on that now.

regards Antony

Hey Anthony,

I am working on a project with that CANbus-shield as well… If you are using the D-Sub keep in mind that the pins are NOT compatible with the CANopen standard(CAN Bus Pin Out, and CANopen pinout, with Signal names), often used in automotive section.

Best
Stefan

Hi Stefan. Thanks for the tip :). No I did not notice that...

Having read through the data sheet for the mcp2515 and the timing data sheet that Coding pointed out has left me with a head that’s ready to pop. I am trying to read the bus at a speed at 138.24kbs and I cannot see past the text on how this is done... Any help here please. Now for the typical beginners questions...... I am looking at the connections that’s need to read the canbus. Am I correct in thinking that’s its only ground. canH and canL that are connected ?? Is there a way of telling which wire is Can high or Can low. ?? I have downloaded a few examples. sketches and libraries for the Canbus card.. Is there a sketch that just reads the data ??

Regards Antony

Hi,

You need connect to CAN_H and CAN_L (don't need gnd). The best way to know which one is which.... an oscilloscope! ;) How do you know the bus speed is 138.24kpbs? In the mcp2515, the registers CNF1,CNF2 and CNF3 set the speed. You can use the software tools recommended before (You need to know the oscillator frequency of your shield).

I don't know if you could find useful the info in http://secuduino.blogspot.com/2011/02/faq.html (you need to use google translator for this FAQ as it's in spanish). You can find the schematic of the brick we have designed in the repository.

Another good one is http://www.kreatives-chaos.com/artikel/ansteuerung-eines-mcp2515 (in German).

Regards,

Hello Igor. I worked out the canbus lines . The canbus speed on Videorays are 138.24 as on page 2 of the site listed below. http://bib.irb.hr/datoteka/306954.paper_CAMS07_final.pdf My shield crystal is 16mhz into the MCP2515. the big issue that I am having is that I cannot get a good match to 138.24 or close...

I also have a snipet of the data I am trying to axcess.

Information of the 7 Bytes VideoRay Sends
The first 3 bytes of the 7 bytes contain an identifier then compass low byte,
compass high byte, pressure low byte and pressure high byte.
All data is in hex.
1) 40 (All VideoRay models)
2) 31 (All VideoRay Pro III)
3) 02 (data type for future use)
4) Low byte of Orientation
5) High byte of Orientation
6) Low byte of Depth
7) High byte of Depth
The relation between low byte, high byte and the real value is:
Real value = Low byte + 256 x High Byte, for instance:
Orientation* = Low byte of Orientation + 256 x High Byte of Orientation (0-359)
Depth = Low byte of Depth + 256 x High Byte of Depth (0-1023)

Many thanks Antony

It seems you could achieve that speed with a 10 Mhz oscillator.... I've done a quick check in http://www.kvaser.com/zh/support/bit-timing-calculator.html If you have MB Time installed, maybe you could double check it....http://intrepidcs.com/modules/CmodsDownload/upload/Software/MBTime.zip

It should not be a big issue change the oscillator... shouldn't it?

;)

Hi Igor. No I cannot change the crystal... No experience with SMT. The only other way is to breadboard the circuit with a 10mhz crystal. I can get quite close to 138.24...133.33 but I have no idea if this is to far away the target. The Kvaster is good.thanks Antony

Hi. Just a update.. Have made a new PCB with all the chips on and the required crystal. Just a note on the crystal for a speeds of 138.24 the best crystal is 11.0592 MHz. Have found a easy reading information on the Canbus and the AVR. http://www.avrfreaks.net/modules/FreaksArticles/files/23/CAN%20on%20the%20AVR.pdf If you are going into the Canbus this is a must read.. Will report back on my findings late next week. Regards Antony

Hi. Just a update.. I am using the circuit and code from http://modelrail.otenko.com/arduino/arduino-controller-area-network-can I have changed the crystal to a 11.0592 as this matched the can speed with NO errors at 138.24. I have also changed the bit timing registers to CNF1 0x01 CNF2 0x0BA CNF3 0x07 I can read the can BUT its all the same and the data should be changing with movement and direction. DE F6 A6 9E 63 F7 7 7C 6C 3F 5A EC DE EC AA 5C DE F6 A6 9E 63 F7 7 7C 6C 3F 5A EC DE EC AA 5C Endless repeating. I am not that good with Arduino and this confuses me?? Any advice on how to overcome this please.

Regards Antony Edited : Update

Hi Just bumping this thread. Been working on this for 2 weeks and not making any headway.

Regards Antony

Hi Just added two of the boards to the puzzle. Will only use one. http://www.mikroe.com/eng/downloads/get/1781/can_spi_click_5v_manual.pdf I intend to use this board rather than my own just in case I have errors in my breadboard. I have come a long way into the CanBus but I still don't have enough knowledge to compleat my mission. As stated before I am using The code and library's from. http://modelrail.otenko.com/arduino/arduino-controller-area-network-can But modified code and library's for the can speed of 138.24.

I have time next week to sort this and I am open to ANY suggestion's (if nice).

Regards Antony