Simplest way to transmit digital data?

Question

I have an interesting problem that's been wrecking my brain and would like some help with it.

Basically what I have is a voltage readout box that has a few voltage displays on it. I would like to have a second box with the same set of voltage displays some distance away. What I'm trying to figure out is the simplest way to send data between the two boxes. Also since this is a high voltage and high electrical noise environment I'd like to do it with fiber optic cables. Now I've done this before with things like CAN-bus or Ethernet/IP devices and it works just fine. The issue is that they all require a controller and some level of programming. I'm working with some folks who would like to stay away from programming as much as possible, so I'm trying to figure out if what I want to do can be done in hardware only.

For instance here is a simple idea of how I envisioned this to work:

• First box has an Analog-Digital converter that reads in the voltage
• This ADC outputs digital data, let's assume it's 8-bits, on 8 separate lines
• I take the 8 lines and convert them to optical signal using 8 fiber optic transmitters
• Take 8 fiber optic cables and run them to the second box
• In second box I have 8 fiber optic receivers that convert optical input into digital output
• Digital-Analog converter reads in the data and converts it to analog output
• Display data on a voltage readout

That sounds fine, except that I need 8 separate fiber optic cables. But if I need to read out 5 different voltages then I'd need 40 cables total, which starts to get ridiculous.

Obviously, the right thing to do is pick some sort of serial transmission that can be done with a couple or few cables. But then I'm stuck with the same problem that I stated above, need to program the thing.

Anyone know of a simple digital communication technique that would allow me to do what I want without having too many cables run between the boxes? The speed of thins thing is not critical, it's all in "human time". Mainly done for safety and monitoring, so a 1 Hz rate is plenty.

Thanks.

Answer 1

If you have easy access to the actual analog signals, the easiest sollution may be to simply pass those analog signals directly to suitable meters in the second location.

Edit: I once designed a system using ADVFC32 voltage-to-frequency converters to transfer signals over optical fiber. The ADVFC32 also works as a frequency-to-voltage converter, so I was able to use the same PC board for both ends of the link. I do have all the design files, unfortunately they are in an old Altium format I can no longer read...

However, look into the ADVFC32 - it may do what you want with no computers. The system accepted and delivered 0 - 10 volt signals. The maximum frequency on the fiber was only 500 kHz

Answer 2

I'd go with SPDIF just because it's easy to implement and not hard to figure out. You'd need two cables and a micro for translation between ADC's

This is a transmitter circuit, not to complicated. And the link shows a receiver Connecting Toslink TORX179L optical receiver directly to S/PDIF coaxial input

Source: https://circuit-diagramz.com/optical-spdif-output-schematic-circuit-diagram/

Answer 3

Amongst the many solutions to this X-Y problem (I mean, can't you put a ready flashed Arduino in a small box and say it's 'hardware'? If they need to fix it just unplug it and plug in the spare)...

How about five parallel V-F-opto-F-V-voltmeter channels?

• Low density of links. From your OP you seemed to be happy with 8, unhappy with 40, so 5 should do.
• All links identical. Spares should any channel go down. Four working ones to compare with any channel that's not working. Swap Tx and Rx ends to determine which is failed.
• Modest accuracy, reasonable speed.
• Easy to comprehend what's going on.

Use a 4046 PLL chip for each end. Just the VCO at the transmit end to give V2F conversion. Send a modest frequency over your opto link, so can use the very cheapest grade of opto components. Use the whole PLL at the receive end for F2V. Send the demodulated voltage to a voltmeter. Even use identical boards for both Tx and Rx end, reconfigured with jumpers.

A much tidier solution would be to buy something like an Adafruit PyPortal, only $55, has a large display, and is python programmable. Multiplex your five V2F senders in hardware onto a single optical fibre, with some protocol like pulse length to distinguish the channels (and mux in some calibration GND and V_FSD levels for enhanced accuracy) and then count the pulses and drive the display. Perhaps one off-the-shelf self-contained piece of equipment might convince them to accept programmable stuff?

Answer 4

Serdes sounds the answer to me. Both TI and Maxim make the same parts under different part numbers and they are interchangeable. Here's the MAXIM diagram: -

I've used them for combining multiple disparate data streams and then uncombining them at some distance away. Should work just fine with the parallel output of an ADC.

Regards using fibre - no problem with these chips interfacing to fibre drivers and receivers to replace the shielded twisted pair shown above.

Ten lines of digital data are provided by the devices so that leaves a couple spare for any conversion ready line (or a sync line) you might also need to feed to the receiver.

• MAX9205 serializer
• MAX9206 deserializer
• SN65LV1023A serializer and SN65LV1224B deserializer

Both TI and Maxim parts are interchangeable.

Picture above from here.

Answer 5

Get your favorite embedded system of choice to interface the meters (Raspberry Pi or similar), run a web server on it that has a CGI interface to the sensors. Then use Ethernet-to-optical for the back haul connection. On the outside you could use any system you want, including some kind of industrial PC with a touch panel, which has a web client to display the data.

If this sounds like ‘programming’ it is. But it will be a lot less effort for a one-off than inventing some serdes protocol.

That said, DMX512 over optical could also do this. This might be more in the spirit of your question. DMX512 is very doable on an Arduino or similar lower-end micro board (yes, ‘programming’ again, but you also said ‘simplest’.) The ‘head’ would be your unit in the HV room, and its ‘universe’ would be the meters outside. Very regular, very predictable, set it once and forget it.

Either way you’ll need to figure out the data acquisition part that works in tandem with the existing meters. To me, that’s the more challenging part of the system given the hazardous voltages involved.

Answer 6

These exist in “low cost” ;) commercial solutions.

I assume you would choose the UNIdirectional 8 ch. but it supports up to 16 analog channels + 32 digital channels BIdirectional with WDM Splitters.