Transmit data via RF

Hi @zaeng,

I haven't done this, so there may be others who can give a more experienced view.

However, the first question is what data rate is required? (Can you change it for both ends, i.e. your display board and the device you are control the display with?)

Range may also be an issue, but if it is 'line of sight' and you can fit a suitable antenna at each end, this may be solvable.

I mention this because the first 'cheap, off the shelf' items offering 433MHz operation I found, stated max data rate of 4.8kbps (max) , another said 4KB/S (max).

Best wishes.

See Bill's excellent adventure at

http://dronebotworkshop.com/433mhz-rf-modules-arduino/

Hi @will and @zaeng,

  Thanks Will for an excellent call to Bill's article ... I hadn't noticed that one before ... and just reading through the forum printout it is clear Bill has done a great introduction. The modules he used looked similar to the ones I found.

The only specific data rate discussion in Bill's article that I noticed was "a relatively slow speed". I didn't see a rate in the code in the forum article, but following the software link, and "RH_ASK" in the code, I came to http://www.airspayce.com/mikem/arduino/RadioHead/classRH__ASK.html

This says "speed=2000". Presumably, this is the default value that the scripts Bill provided would use.

I haven't looked, but I guess this could be changed to the standard rates like 1200, but the hardware will probably limit the maximum supported rate. I am concerned the display board (or sender) may insist on a rate that is higher than this value. (Of course, other radio hardware is available but my natural instinct is to start cheap and work upwards when the need has been established.)

How much data do you need to transmit (and how often) ?

@will

I am not sure yet , but it i think it is tiny .

you are sending time or speed to the display once 3 mins 

time : example 29.7 sec 

speed : 101 km/h 

regards 

no units only the value 

@zaeng

If you're really sending only 8 bytes every 3 minutes, then the 433mhz modules will be more than adequate, depending on the range. How far apart will the timing and display stations be ?

Also, will thereby anything else broadcasting or any high energy discharges in the area that might interfere with the RF transmission ?

Hi @will & @zaeng,

  Obviously that rate of data update is unlikely in itself a challenge to any conceivable system.

However, I am assuming your hope is to replace the wire between the control/sender unit and the display unit, with a simple radio link. (i.e. no 'smart stuff' like arduinos)

The link you provided says "interface RS232 and RS485", but I couldn't find any details of bit rates (baud rate), etc. Hence my original questions which are so far unanswered.

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In principle, it should be fairly simple to connect RS232 or RS485 interface almost directly, to send the bit stream by radio in a manner that Bill demonstrated, providing the interface voltage levels are converted as required.

However, if say you select RS232, and the data rate for the display interface is fixed at 9600 bits/sec, then the transmitter/receiver specs of 4k and 4800 max that I saw, cannot be expected to work. On the other hand, if it operates at 1200 bits/sec, then life might  be much easier. Sometimes, these parameters can be readily changed at the equipment (both ends), but not always.

Of course, if you add some 'smartness', like an arduino, at each end of the link, which can convert the data rate bits, then the problem can be resolved, albeit at increased expense of cost and complexity.

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Before committing to a course of action I would advise ensuring that the data transmission is only in one direction. It is conceivable, if unlikely, that the communications might be bidirectional. That is not say a radio link can't be done with a bidirectional link, just that it needs a different approach.

For RS232, check that the only interconnecting wires are just one data wire and its '0 Volt/ground' return .. the 'original' RS232 standard includes several 'status' wires, as well as a data in the reverse direction.

RS485 typically has two data wires plus 'ground'. It can be uni- or bi-directional, the wiring doesn't change, only the protocol adopted.

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Once you understand the interface, hopefully the path forward will be much easier.

Best wishes, Dave

@davee

Good point(s) !

It never even occurred to me that there wouldn't be an Arduino (or some kind of "smartness") at both ends.

Hi @will,

  It is probably just me showing my age ... when I started playing with electronics, 'germanium transistors' were the still the new-ish kids on the block, with valves (tubes) still very much part of the scenery.... computers were probably rarer than quantum computers are today😀 

Plus, a 'belief' that understanding as much as possible about a problem, before drifting into the solution, is usually the best practice, eventhough it can be very dull and frustrating at the time.

Best wishes!

@davee

I understand, I'm old too 🙂 Started fooling around with transistors back in high school, they were new and expensive then, but a lot more convenient than tubes 🙂 Never had enough time or money to keep it up but decided to start over on electronics a few years ago.

Bad timing on my part. Deciding to try to use tiny parts with big clumsy hands, a short memory and the attention span of a weasel after a double hit of espresso 🙂

@davee

Hello 

I am unsure of the data transmission rate , but will enquire 

My guess is that it only 1 direction , 

regards

ZA

Hi @zaeng,

If you look at the RS232 interface connections, you may be able to determine if there is just Rx (receiver) data, or Rx and Tx (receiver and transmitter) data lines (in addition to ground/return wire in both cases). The former would imply only 1 direction is possible.

As for data rate, the manufacture should be able to help, otherwise measurement is required. (Assuming nothing visible on either end, such as baud rate switch.)

An oscilloscope would be the easiest, but obviously you may not have one..

You specified the display, but not the 'sender unit', or which interface (RS232 or RS485) is being used. RS232 and RS485 use different voltages, as well as RS232 being point-to-point, whilst RS485 is multidrop, so they normally specify different interface chips.

If it RS232 ... then ...

If you have a 'older' PC with an 'old skool' RS232 serial port, then combined with a (free download) terminal program, you could try connecting the sender unit, using different baud rates, looking for one that sends recognisable characters, assuming the protocol is ASCII based or you can interpret the binary (hex) values. Unfortunately, there are a lot of 'if's that can make this process difficult, with hardware and software issues, including Windows, all able to conspire to make it fail.

Similarly, an Arduino or similar, could be used instead of the PC, but you MUST have an RS232 interface at the 'front' of your Arduino to convert the RS232 voltages (typically around -12V to +12V to the logic levels of 0 to 3.3V or 0 to 5V of an Arduino.... otherwise your Arduino is likely to become a deceased Arduino.

I haven't used one (or shopped for the best deal), but something like https://thepihut.com/products/max202-rs232-to-ttl-converter-for-arduino should work if your Arduino has 5V logic interface.

If it has 3.3V logic interface, then either find an equivalent RS232 converter with 3.3V logic interface,  or interpose a 5V to 3.3V logic converter as well as the RS232 interface

Hope this helps .. sorry it isn't vastly complicated, but if you haven't worked with these interfaces at the chip-level before, then there are lots of hidden traps that are difficult to diagnose with only minimal test equipment.

Posted by: @davee

Of course, if you add some 'smartness', like an arduino, at each end of the link, which can convert the data rate bits, then the problem can be resolved, albeit at increased expense of cost and complexity.

@will @zaeng

It is true that with a fully stocked electronics bench, raw and simple RS232 might be cheaper than an Arduino. And it may also be a fun project.

In my case, though, I just buy some more Arduino Nano clones, maybe a 6-pack, and call it a day. I also use the little inexpensive breadboard power supplies, and the similarly inexpensive adjustable buck converters for my power.

I did follow the @dronebot-workshop video on different kinds of power for my projects. So in theory I could wire up a low drop out regulator, but I don't have that regulator, or any capacitors, or any transistors. I only recently got an assortment of resistors to go with the mix of LEDs in a little kit. 😯 I'm getting there, but it seems I spend half my life on Amazon or Aliexpress. So we all come from different places, and I'm glad to have the ready-made modules for various purposes.

For Zaeng, good luck with the project.

Hi @jbo,

 Your comment ...

it seems I spend half my life on Amazon or Aliexpress

                     is all too familiar at my end as well.... 😀 

As for the the project under discussion. Not knowing the baud rate, and other parameters like 7 or 8 bit word, even or odd or no parity, and so on, could make it tricky, even with a spares box full of Nanos, if you don't have an oscilloscope handy. Of course, you might strike lucky first time, but if it is an odd combination, then some cunning may be needed to find it.

However, if (and it is a big IF) the system bit rate is low enough for the transmitter/receiver combination, then it should work without needing to know the other parameters providing you can match up voltages, etc. since the bit pattern should be preserved as if there was a simple wire link.

As always, the most important starting point is to discover the exact requirements of the job.

Good luck and best wishes to everyone!