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Original question:

I need a switch to multiplex UART to 4 sensors

UART Multiplexing

Gerald
Genius 9570 points
Other Parts Discussed in Thread: TMUX1511

Hi Experts,

Our customer is busy with research on GPS systems and the application of low cost GPS in the industry

The challenge that he has are as follow:
I have a single stand-alone low-cost sub-decimeter GPS that transmits data via it's UART.
I need to have that data sent to 4 different devices simultaneously
I have purchased 2 different units from Mikro E that claims that in their descriptions but it is not the fact.
The data is a mixture of GPS and AIS data and is straight forward
Do you have an answer for my challenge?

Trying to help our customer with this concern, I was able to see this thread below and shared this to him accordingly:

I also provide this app note below as initial information for him to browse:

However, he said that he has zero knowledge of electronics and does not quite understand the links I sent to him.
He said that he has spent a small fortune on products from MikroE that claim to be able to do what he wants to do but does not.

He also said that he has seen this done many years ago using telephone company-wide area data network and a 9600 baud modem that connected
to a multiplexer/de-multiplexer.

He asked various other suppliers but received no replies to date.

If you have a recommendation/solution for our customer concern please advise. Thank you so much.

Best regards,
Gerald

  • 0
    Guru 316440 points

    For unidirectional data, no switch should be necessary. In theory, you could simply connect the TXD output of the GPS to the RXD inputs of all four devices. If the load is too high, it would be possible to insert buffers.

    What are the electrical characteristics of the UART I/Os of the GPS and of those four devices?

  • 0
    TI__Mastermind 24440 points

    Hello Gerald, 

    I agree with Clemens on and would like to know the  answer to Clemens questions.

    Clemens Ladisch said:
    What are the electrical characteristics of the UART I/Os of the GPS and of those four devices?

    Regards,

    Kameron

  • 0 in reply to Kameron Hill
    TI__Genius 9570 points

    Hi Team,

    Below is the information from our curstomer:

    "I have done that and I get data for a couple of seconds after which the port dies and I have to restart everything.
    I have purchased 2 units from Mikroe but they only allow 1 of 4 ports to be used at a time rendering them useless for my requirements
    I require the data continuously.
    I can monitor the data going out and that is correct.
    On the receiving end I am not getting anything.
    For now it is unidirectional but in future bidirectional communication would be required.
    What I am trying to achieve is to use one of my GPS devices as a reference station with 2 or 4 similar devices connected to it all receiving RTCM and AIS data from the reference unit."
    Best regards,
    Gerald
  • 0 in reply to Gerald
    Guru 316440 points

    To send the data from the one GPS output to four other devices, nothing additional is necessary; just connect them together.

    To send the data from the four devices to the GPS, you need a multiplexer to choose one of them, or just an AND gate if you can guarantee that no two devices are trying to send at the same time.

    The information given is not enough to diagnose the problem. As a start, I would need at least the schematic of the entire circuit, or at least the part numbers of all devices.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 24440 points

    I also agree with Clemens could the customer send a schematic to help us diagnose the problem. I think the Tmux1511 would allow the customer to control have four signal paths on at the same time but the customer schematic will really help here!

    Regards

  • 0 in reply to Kameron Hill
    TI__Genius 9570 points

    Hi Team,

    Please see below information from the customer:

    "I have tried to do that.
    There is no schematic.
    What I have is four C94 EVK GPS units.

    One of them is set up as a Reference station that transmits RTCM correction information via its onboard UART. I can wire the GND to GND, TX to RX and RX to TX on another unit. Doing it like this works perfectly and the roving unit receives the data and applies improving the position.

    The moment I add another roving unit the data is transmitted to both roving units for a few minutes upon startup but then both stop receiving the data stream. The same goes for 3 roving units.

    I also have a number of Leica SR 500 GPS units, they have proper RS232 ports and does exactly the same as the UART ports on the UBlox receivers. Thank you"

    Best regards,
    Gerald

  • 0 in reply to Gerald
    TI__Mastermind 24440 points

    Hello Gerald,

    Can the customer take a picture of the setup? This would really help solve this issue. 

    From what I am reading it looks like the customer is  trying to monitor all 4 at the same time, but its just 1 data line. If all 4 models are talking on the same line it'll be too busy with every model conflicting. He needs 1 TX pin and 4 RX paths on his MCU.

    Also can you show the customer this FAQ that is an overview of Ti multiplexers. Here is another FAQ that can help the customer understand uart.

    Regards 

  • 0 in reply to Kameron Hill
    TI__Genius 9570 points

    Hi Kameron,

    Please see below information from the customer:

    Attached is an image of 3 units.

    The center one is set up as a Reference station and the other 2 as Roving units.
    The fourth unit is presently being used on a different project and I will be adding it soon.
    Each of the receiving units perform a different function in that the one does RTK for positioning, The other one AIS and the the last one when I add it
    will be used to provide NMEA data to an autopilot
    As is said if I daisy chain the ports from the reference unit TX I used a Y cable to the RX ports of the roving units and the same from GND, I can see the receiving units receiving the correct data for a few seconds after startup and thereafter nothing.
    I also power them from the same source
    What you describe is exactly what I require. I just have no idea
    It is not the best image and it is still attached to the UART MUX that I bought from Mikroe that does not work
    Thank you
    Best regards,
    Gerald
  • 0 in reply to Gerald
    TI__Mastermind 24440 points

    Hello,

    From what I am seeing it looks like the customer is  trying to monitor all 4 at the same time, but its just 1 data line. If all 4 models are talking on the same line it'll be too busy with every model conflicting. He needs 1 TX pin and 4 RX paths on his MCU.

    This might require purchasing another MCU.

    Regards,

    Kameron

  • 0 in reply to Kameron Hill
    TI__Genius 9570 points

    Hi Kameron,

    Please see below information from the customer:

    Yes, I have a single transmission source. 
    The source transmits data required by the other devices to perform specific tasks.
    Device 0 is the source, device 1 is a roving unit and requires the rtcm data for rtk.
    Device 2 is an AIS device and requires the NMEA data to perform its task. 
    Presently devices 3 and 4 are not being used but will soon be used 
    Thank you
    Sincerely

    Regards,

    Gerald

  • 0 in reply to Gerald
    TI__Mastermind 24440 points

    Hello Gerald,

    Because the module is only working part of the time I would recommend you to contact the manufacturer because this problem may not be coming from the multiplexer.

    Regards,

    Kameron