can bus circuit

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Joined: Thu May 11, 2017 11:08 am

can bus circuit

Postby tuflix » Thu May 11, 2017 11:15 am

I am new to this forum, so I want to take the opportunity and say hello to everybody.
4 months ago I discovered arduino, and since then I've been playing a lot with it doing basic stuff like controlling leds, using it with various sensors, servos, etc. Recently, I came across esp32 which seems to be the newest and coolest kid in town and I'd like to start using it for a small home automation project I have in my mind. My first goal is to have a couple of esp32's spread around the house and use can bus for communication. I am an experienced programmer, but when it comes to electric circuits I am an absolute beginner. I stumbled upon one of the products from olimex (ESP32-EVB) which is build around esp32 wich includes a canbus circuit. The good part is that it's open source, the bad part is that I have some difficulties understanding their circuit - the areas that are highlighted with red from this screenshot ... 8099a3.png . I suspect that area 1 from the circuit is some sort of a logic converter, but I don't understand how can I put it on a breadboard. 2 is probably a jumper, which once mounted, adds 120R resistor to mark the end of the can bus line. I have no idea what 3 (PWR_FLAG) means. The schematic for the whole board can be found here ... _Rev_B.pdf
Any help will be appreciated.
Thank you.

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Joined: Tue Dec 01, 2015 7:35 am

Re: can bus circuit

Postby WiFive » Fri May 12, 2017 8:05 am

1. MCP2551 is 5v chip. Power supply choice is probably to give you (or them) the option to use a 3.3v chip. So if you are using MCP2551 then just ignore and connect to 5v. Level shift is done by 330/680 resistor divider.

2. Yes for bus termination

3. This is just notation for the software to tell it which connections are part of the power supply.

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Joined: Fri Mar 17, 2017 12:13 am

Re: can bus circuit

Postby iosixllc » Mon May 15, 2017 10:04 am

And PLEASE, if you are connecting to a vehicle, use a proper automotive transceiver instead of the MCP2551 piece of junk. TJA1042TK/3 would work fine and has the correct logic levels for the ESP32.

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Joined: Thu May 11, 2017 11:08 am

Re: can bus circuit

Postby tuflix » Mon May 15, 2017 10:36 am

I am not interested in connecting the esp to my car, I just want to experiment a bit with can bus to see how suitable would it be for a small home automation project that I have in my mind. So far, the results are encouraging. Instead of MCP2551 I used SN65HVD230 (3.3 v logic). It simplified the circuit and it worked flawlessly across a 120m cable with 2 termination nodes. I used the can driver from here ... onents/can

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Joined: Sat Jun 10, 2017 8:43 pm

Re: can bus circuit

Postby cliftonk » Mon Dec 18, 2017 3:50 am

Hello tuflix,

Can you please post a schematic of your circuit and BOM?

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