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serial transmission from several digital sensors

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cts_casemod

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Hi,

I have a bunch of sensor signals that I want to transmit using a single serial data line, instead of one wire for each. There is a lot of information on serial to parallel, but what do I need to convert from parallel to serial? Can I just use a 555 for clock and some kind of shift register? to put back the data at the other end? Regards
 

You just need to pack the data from all these sensors in a known frame format, so that exact sequence in which each byte is sent by transmitter will be addressable on receiver side meaning the acquired value of each one.


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Can I use the same line for say both transmission and reception? Regards
 

Use modbus protocol by which you can communicate with each sensor bidirectional (Half duplex).

Google with the term "modbus" you will find lot of information.
 

Excepting GND, how many physical wires do you expect to use ?


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At the moment I have about 16, but I will be using twisted pairs (individual) for all analogue signals as well as the motor encoder, since this is a real time signal, so currently 24 wires with GND

Other (non priority) signals like alternator light, start button, brake signal and so on I would like to carry using only 3 wires + GND. Possibly one line for sending, one line for receiving and another line just for the LCD to show inverter details.

It would be great if I could have one single data line protocol like can bus and could just attach devices with an ID for the receiver. Even better if they could carry the analogue signals as well.

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nandhu015 said:
Use modbus protocol by which you can communicate with each sensor bidirectional (Half duplex).

Google with the term "modbus" you will find lot of information.
Click to expand...

Is there some way I could use it without uP attached? Something like an industrial interface or so?
 
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I can´t see other way to perform this data concentration than using an intelligent control.

Depending on the design complexity you are able to deal, and distance between Tr/Rx, the most common approach is by Ethernet or Serial.
In fact, there are other industrial target options such as Modbus, etc...but much more expensive.


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crutschow said:
That requires an intelligent controller, which is most easily done with a microprocessor.

What is this "bit"?
Click to expand...

The original idea was to have a clock line and 3 transmission lines: One for the LCD, Another for the inputs and a third one for outputs, each of them operating in 8 bits parallel to serial and converted back to parallel on the other end. Much better than having 24 wires. Of course analogue data is sent on individual lines, each with its own pair (Signal + GND).

This bit is an LCD interfaced to the inverter for a 3 phase motor on my Electric car. Currently I don't have any feedback from it because its on the back of the car, I would like to have the LCD on the center console.

Regards
 

What is the distance between this remote devices "concentrator" and the host ?


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I just read a lot of quite complex ideas. I think I can suggest a simple one. why dont you use a 16:1 mux?? you will surely need 4 control lines, but that can be on board. You just need to create some gap at the beginning and ending to signify the start and end of the reading. Apart from that, you'll need to create a bit of synchronization between transmitter and receiver (the way its done for UART).
I think with this implementation, you wont even need a smart controller.
 

shatruddha said:
I...I can suggest a simple one. why dont you use a 16:1 mux??
Click to expand...

I don´t like this approach, due some synch loss will not be detectable, and at serial communication may introduce check bytes, such as CRC.
Once will be used a dedicated PCB, I don´t see any inconvenience to perform this job by a uC.

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andre_teprom said:
What is the distance between this remote devices "concentrator" and the host ?


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Click to expand...

Not much, about 5 meter of cable, the most. I am using UTP cables with twisted Pair to avoid any noise for the motor PWM carrier frequency (2 to 14KHz)

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shatruddha said:
I just read a lot of quite complex ideas. I think I can suggest a simple one. why dont you use a 16:1 mux?? you will surely need 4 control lines, but that can be on board. You just need to create some gap at the beginning and ending to signify the start and end of the reading. Apart from that, you'll need to create a bit of synchronization between transmitter and receiver (the way its done for UART).
I think with this implementation, you wont even need a smart controller.
Click to expand...

I thought about that before, but without a clock signal how do I make sure it wont pick up noise from the carrier PWM frequency feeding the motor?
I can't remember either, can I have bi-directional comms with a mux?

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andre_teprom said:
I don´t like this approach, due some synch loss will not be detectable, and at serial communication may introduce check bytes, such as CRC.
Once will be used a dedicated PCB, I don´t see any inconvenience to perform this job by a uC.

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Click to expand...

I would certainly use one, simple RS-232 Comms would even allow analogue signals to be sent with a few bits resolution, problem is I have no idea how to program :/ :oops:
 
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cts_casemod said:
...I would certainly use one, simple RS-232 Comms would even allow analogue signals to be sent with a few bits resolution, problem is I have no idea how to program :/ :oops:
Click to expand...


It is absolutely comprehensive that you want to keep design as simple as possible, but I must advice that if you perform the task by an uC, the flexibility achieved substantiate the effort required to learn. There is always a first time...


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andre_teprom said:
It is absolutely comprehensive that you want to keep design as simple as possible, but I must advice that if you perform the task by an uC, the flexibility achieved substantiate the effort required to learn. There is always a first time...


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Click to expand...

So in your opinion what would you advise as a good start point?
 

As sugested, start learning and design this board based on uC; It is not very complicated and progress will become faster that you can imagine. I´m not confident if any other solution with no data check will work properly at this electricly agressive environment.


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