Read bus data from OBD interface

hahfhy

Read bus data from OBD interface [Copy link]

I would like to ask all the experts, I need to get the car engine speed from the OBD interface. Through some understanding, I know that there are two ways: 1. Receiving only, that is, reading the data sent periodically by each ECU on the CAN bus from the OBD, and then getting the desired information; 2. Question and answer method, sending a signal request, for example, the engine speed PID is 014C, and then receiving the reply data. The advantage of method 1 is that it is only receiving, has no effect on the car's electronic system, and has a high safety factor. What I want to ask is, can this data be read from the OBD for all cars? Will there be a situation where the data is encrypted and the message cannot be parsed? Since method 2 is a question and answer method, it will occupy the data channel. If the amount of information is too large, it may block the CAN channel. What I want to ask is that if only the engine speed parameter is needed, will the amount of information be very large? If it is read every 20~30ms, will it be too fast and occupy too many resources? Thank you in advance.

开新未来

Thanks for sharing, thank you for your hard work

嘎啦嘎啦带你嗨

1. The engine speed signal IDs of different car manufacturers and different ECU suppliers are likely to be different. Similarly, the DIDs used in the second method to read the speed may also be different. As for encryption, the signal is generally not encrypted, but there will be some check bits. You can ignore these check bits when reading data; 2. The general speed signal cycle is about 10ms. You said that it is okay to read it once every 20-30ms. Generally, the bus load rate will not be too high, so you can rest assured that it will not affect the bus.

hahfhy

Galalagala brings you hi Published on 2018-5-3 09:25 1. The engine speed signal ID of different car manufacturers and different ECU suppliers is likely to be different. Similarly, the second method for reading the speed DID is also...

Thank you very much, very professional. In addition, I would like to ask, if it is a question-and-answer method from OBD, is it difficult to use a CAN transceiver and then analyze it yourself? Thank you

嘎啦嘎啦带你嗨

hahfhy posted on 2018-5-3 09:39 Thank you very much, very professional. In addition, I would like to ask, if it is a question-and-answer method from OBD, is it difficult to use a CAN transceiver and then analyze it yourself? Thanks...

It is actually not difficult, there is a stupid way. After you connect to OBD, keep stepping on the accelerator and releasing the accelerator. Generally, only two signals will change dramatically, one is the speed and the other is the instantaneous fuel injection amount. As for how to distinguish these two, you can parse them according to the binary and compare the tachometer.

hahfhy

Galalagala takes you to have fun Published on 2018-5-25 13:44 It is not difficult to start. There is a stupid way. After you connect to OBD, keep pressing the accelerator and releasing the accelerator. Generally, only two signals will change dramatically. One is the speed.

Haha, good way. I have tested it recently. The question-and-answer method will be more difficult at 10ms. It is still OK if it is more than 30ms. However, it will also cause some car faults to be reported. For example, the high-end Honda Accord model will report a fault in the automatic collision avoidance system as soon as a request is sent from OBD. .

hanwenli123

Galala Gala brings you happiness published on 2018-5-3 09:25 1. The engine speed signal ID of different car manufacturers and different ECU suppliers is likely to be different. Similarly, the second method of reading the DID of the speed is also...

Hello, I have been studying OBD recently. I would like to ask, if the DIY diagnostic equipment only has the CAN protocol, can it read many cars? There are five or six protocols in OBD. How do I know which protocol the car being tested is using?

hanwenli123

I'm learning OBD recently. I'd like to ask you how CAN communicates with the car. Do I need to initialize the CAN interface first? Can you tell me how to do it specifically, or what information should I read? Thank you.

ansonpang

I would like to ask the original poster, what parameter change signal is used to measure the car engine speed obtained from the OBD interface?