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THVD8000: Implementing THVD8010/THVD8000 for 24 VAC Communication System

Dharmesh Joshi
Expert 1915 points
Part Number: THVD8000
Other Parts Discussed in Thread: THVD8010,

Hi,

I am interested in using the THVD8010 or THVD8000 for an upcoming project.

I have a scenario where my main controller or device needs to send messages to multiple points around a building to control devices such as relays and solenoids. Unfortunately, this communication will need to be done over just two wires rather than using Wi-Fi or RF. These two wires will carry 24–30 V AC.

There could be up to 50 nodes on the same line, with a maximum cable length of about 1 km. If I understand correctly, using a lower carrier frequency helps achieve greater communication distances—is that right?

Also, is there a reference design I can use to develop my own PCB that works with 24 VAC?

If I’m correct, these devices use a simple RS-485-style UART interface, so I would need to develop my own communication protocol to handle CRC, polling, and message acknowledgements. I’ve seen other devices on the market labelled as PLC modems, which I assume incorporate these features to provide a more robust messaging mechanism.

Since my PCB already includes an available UART port, my aim is to create a simple and resource-efficient module for the microcontroller—hence my interest in the THVD8010 solution.

  • 0
    TI__Guru* 77791 points
    Dharmesh Joshi said:
    There could be up to 50 nodes on the same line, with a maximum cable length of about 1 km. If I understand correctly, using a lower carrier frequency helps achieve greater communication distances—is that right?

    Yes, there is a trade off to the carrier frequency.

    Faster allows for you to select a lower value inductor (smaller size) but distance will be lower.

    Slower allows you to transmit further distance. (inductor will be larger).

    Dharmesh Joshi said:
    If I’m correct, these devices use a simple RS-485-style UART interface, so I would need to develop my own communication protocol to handle CRC, polling, and message acknowledgements. I’ve seen other devices on the market labelled as PLC modems, which I assume incorporate these features to provide a more robust messaging mechanism.

    ~Yes. The D pin of the device accepts any TTL input as long as it can meet the ViL/ViH and doesn't exceed the max data rate. 

    This device is flexible in the sense you could use whatever single pin protocol like UART. 

    Dharmesh Joshi said:
    Also, is there a reference design I can use to develop my own PCB that works with 24 VAC?

    From a PCB point of view, we mainly just have the EVM. https://www.ti.com/tool/THVD8000EVM

    I do suggest that you take a look at the technical documents we have for this device though: https://www.ti.com/product/THVD8000#tech-docs

    -Bobby

  • 0 in reply to BOBBY
    Expert 1915 points

    Sorry for the late reply; it seems I didn’t receive an email notification that you had responded.

    Is it possible to run some simulations with slower transmission speeds, and what inductor would be suitable for greater distances? I don’t really need something extremely fast, as the goal is to have a robust method of transmitting messages to a node over 24 VAC wires.

    What would be the maximum data rate, in terms of baud rate, that I can set on my microcontroller?

    Also, how does OOK modulation differ from ASK modulation, and is it any better?

    Regarding the EVM kit mentioned in the user guide, there’s a schematic provided — would it be best to start with that design? And is this version intended to work with the AC version?

  • 0 in reply to Dharmesh Joshi
    TI__Guru* 77791 points
    Dharmesh Joshi said:
    Is it possible to run some simulations with slower transmission speeds, and what inductor would be suitable for greater distances?

    I don't think we have a simulation model for something like this. 

    The inductor is used to prevent the carrier frequency from propagating into the power supply lines. I don't think the inductor itself will influence the distance.

    Dharmesh Joshi said:
    What would be the maximum data rate, in terms of baud rate, that I can set on my microcontroller?

    At the distance you're trying to support you likely will need to use the slowest carrier frequency which would be 125kHz. This would amount to 12.5kbps since we want the carrier frequency to be atleast 10x the max data rate.

    Dharmesh Joshi said:
    Also, how does OOK modulation differ from ASK modulation, and is it any better?

    I had to google this one... The THVD8000 is technically doing ASK modulation in it's most simplest interpretation when a frequency present the digital representation is a '0' and no frequency is a '1'. ASK can incorporate multiple amplitudes to get more bits out which is where the advantage would be. 

    Dharmesh Joshi said:
    Regarding the EVM kit mentioned in the user guide, there’s a schematic provided — would it be best to start with that design? And is this version intended to work with the AC version?

    https://www.ti.com/lit/an/slla590/slla590.pdf?ts=1761778947633&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTHVD8000

    I would suggest taking a look at this document.

    We have quite a bit of technical documentation in this section of the product page. 

    https://www.ti.com/product/THVD8000#tech-docs

    There is also a reference design: 

    https://www.ti.com/lit/ug/tiduf48c/tiduf48c.pdf?ts=1761779027797&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTHVD8000

    -Bobby

  • 0 in reply to BOBBY
    Expert 1915 points

     I will read the document. What sort of max distance could we achieve with 24VAC on the same wire?

  • 0 in reply to Dharmesh Joshi
    TI__Guru* 77791 points

    I think this will probably depend on the wire quality and the connection topology of the network but I think you can achieve 1km if the data rate is set to a lower rate.

    -Bobby