Wireless serial Relay? Would this fail?

Basically since my land based FPV drone is in and around obstacles much more so then a regular drone. I would like to set up 3 HC-12's. one transmitting one receiving and transmitting and, one receiving. Can the 3 HC-12's Co-exist on the same frequency Thus leaving one Arduino to listen to two modules while both are in range? Will the two modules on the same frequency interfere even though they are transmitting the same data? Timing? Things I need to know Im sure. Thanks in advance.

The answer to the question "Would this fail" is always YES - no matter what the question is about. The real question is whether something would fail so often as to be useless.

Logical lesson finished :slight_smile: ...

If any pair of transmitters on the exact same frequency (both within range of the receiver) transmit at the same time the receiver will get garbage. I am not familiar with the HC12 but I know the nRF24L01+ transceivers have an auto-retry capability. That is likely to make things worse, not better, because they will both be retrying.

If you have two transmitters on different frequencies (channels in nRF24 parlance) they may still interfere with each other if the devices are very close together. I have not tried but they might work if they use widely separated channels.

I don't know if the HC12 has an auto-acknowledgement feature like the nRF24 but, if it has, you will almost certainly need to turn it off with multiple devices on the same channel thus losing one existing layer of protection.

I can't help thinking that your idea introduces so many additional complexities that it is likely to reduce overall reliability. One of the problems you will face is finding a set of test situations (i.e. drone in one place and controller in another) that will properly exercise your system to the point where you can have confidence in it.

...R

PS. I was originally assuming that you are thinking of having 2 HC12s on your drone but on re-reading your Post I wonder if you are thinking of having an extra ground-based relay station so that either the relay station or your controller would be in contact with the drone.

If that is what you have in mind I think most of what I already said remains relevant. And the relay station would introduce the extra complexity of a slight delay in the propagation of the signal. That delay may not matter for control purposes but it could cause confusion when the controller (or the drone) is getting the same message twice at slightly different intervals.

It might be made to work if there was some means to switch between the two message routes so that they cannot interfere with each other. But I suspect that would be complex. Maybe the relay station could operate on a different channel and if the drone failed to get regular messages on channel A (from the controller) it would switch to listening on channel B for the relay station and vice versa.

...R

jgreene33:
I would like to set up 3 HC-12's. one transmitting one receiving and transmitting and, one receiving.

What are the HC12s actually being used for, and why did you choose that module ?

Awsome response and thank you soo much for taking the time.

Your logical lesson is undeniable. always lol.

I understand all of what you are saying. So you are following me yes your second thought was correct. the relay would be set up some hwhere away from the original transmitter so the relay and the original transmitter can both speak to the drone. More specifically. The relay would be situated as to extend range. As for the gentleman that asked why HC-12. 433Mhz attenuation vs 2.4Ghz attenuation. As for what I do with them. Well I put them in my butt. They make my
dookie transmit data.

Questions I am left with. Thanks to Robin2:

Time based segregation of incoming signals via Arduino code?

Switch the relay on/off based on drones position? Seems interesting. I think I like this idea I believe you mentioned this? Obviously two will have to be sending data to the drone at one point due to the
fact that the original transmitter must remain active. However, once the drone reaches the end of the
transmission range of the original transmitter. Could I then cut on the relay that is now actually closer to the original transmitter then the drone is. My initial thought is perhaps in this orientation the relay will drown out the signals coming from the original transmitter thus making the multiple signals a non-issue.

I am aware there are ways to setup a WIFI intranet However I cannot think of any other ways to setup a wireless web if you will.

jgreene33:
As for the gentleman that asked why HC-12. 433Mhz attenuation vs 2.4Ghz attenuation.

I have a little experience in RF things, so I realise that 433mhz is a better choice than 2.4ghz in terms of range.

Have you actually used the HC-12s for any repeater type applications as they would appear to be close to the worst possible choice (of 433mhz modules) for what you are suggesting ?

As for what I do with them. Well I put them in my butt. They make my dookie transmit data.

Can you provide an explanation of what that means please ?

jgreene33:
However, once the drone reaches the end of the transmission range of the original transmitter.

I suspect you have a major misconception here which might be underlying (and undermining) your whole design.

The end-of-range will be incredibly vague. I doubt if you could define it to anything better that +/-50 metres, or maybe only +/- 100 metres. It will be different in different weather conditions and with different levels of interference from equipment you are completely unaware of.

To my mind it will be essential to operate the base station and the relay station on different channels (frequencies). - but I don't know if that concept exists with a HC12.

Conceivably you could have two HC12s on the drone each listening to a different channel but only one of them transmitting at any one time. But will the extra complexity to manage all that add to overall reliability ???

...R

Same freq. Robin2. I am was merely thinking out loud that perhaps that could work. signal starts to fade drastically at a certain point on any rig. Once the drone starts to register around -110db. That should
Trigger the relay to come on. Once again. Your drone has now traveled past the relay by a considerable amount. its maybe at a mid point or 3/4 of the way to you. The relay at this point now has better range on both the original transmitter AND the drone. If the relay was at the 3/4 point it would have a ton more signal going to the drone at this point. Could we not segregate via amplitude? Heck I am sure we can. Question is how? and how
hard would that be. None of this would I consider part of my plan though my freind. This started with me only asking. Now I am thinking out load based on the things you stated that triggered some idea's. Forgive me if I am ahead of myself or speaking out of turn.

As for have I used these before in such an application? I am sorry srnet. I feel like you are not following
along well at all. No of course not. This is the sole reason I am looking for advice? Also as far as I know.
There are only a few 433mhz wireless transceivers available that put out 20db+?

This is me being humorous:
"As for what I do with them. Well I put them in my butt. They make my dookie transmit data."

Basically you insert the module into your rectum. Energize the module. Feces will adhere to the module. Allow the Fecal matter to pass into the receptacle (toilet). Energize the receptical Allowing the module to once agian power and, at this point with proper coding and when in range. your feces or "Dookie" can transmit data. Its on the front page @ allaboutcircuits. Sadly Dookie cannot currently transmit @ 433Mhz.

jgreene33:
This is me being humorous:
"As for what I do with them. Well I put them in my butt. They make my dookie transmit data."

Yeah. I figured that was all crap.

Could we not segregate via amplitude? Heck I am sure we can

I suspect not - certainly with 2.4GHz wireless the RSSI is almost useless.

And you can't segregate two overlapping signals on an identical frequency - they just interfere with each other and you can't receive anything.

...R

I am not so sure. With over 100db of seperation. the signal from the original transmitter should be able to be filtered out as noise?

jgreene33:
I am not so sure. With over 100db of seperation. the signal from the original transmitter should be able to be filtered out as noise?

I have no idea. Have you done any tests? The Arduino system is ideal for doing quick and dirty tests to explore ideas.

...R

Robin2:
To my mind it will be essential to operate the base station and the relay station on different channels (frequencies). - but I don't know if that concept exists with a HC12.

You can set the channels on HC12s but its really a once off type setup, they do not have the ability to rapidly shift channels or frequencies.

There is no error checking of the serial stream either, so you would need to add your own checksums.

There are low cost radio modules that are frequency agile with built in error checking (so send and ack\nack is possible) that are around the same price of a HC12 and they go very much further to boot.

jgreene33:
I am sorry srnet. I feel like you are not following along well at all.

Your original post did not describe what you are actually trying to do, and you still have not explained.

You apparently want to get 3 HC12s to communicate over a long distance, but wont provide any information as to why, what function they are performing or what the environment or distances are.

I wish you success in your endeavour.

Hi,
I think the OP wants a system that provides a complete RC coverage for his drone while it is working in an area where obstacles will compromise a single line of sight RC system.

Google " antenna diversity " this is probably what you are looking for.

Tom... :slight_smile:

Robin2 and TomGeorge. Thank you very much. Its great to see interest in solving this. I will on both accounts find the answer. srnet you are silly. but thanks anyway.

Will post back as soon as I get some results! For now I've not the time. Gotta go earn a living :(.

TomGeorge:
Hi,
I think the OP wants a system that provides a complete RC coverage for his drone while it is working in an area where obstacles will compromise a single line of sight RC system

Maybe, but I can think of a few reasons why you might want to setup 'communications' with a land based robot (drone ?), they are not all radio control based.

However rather than provide answers to reasonable questions, the OP responded with poor humor and derogatory comments, making clear that he\she was not going to reveal what they were actually up to.

Commercially available RC tx/rx pairs will do a better job than a start-from scratch amateur relay system. Not easy.

Channel agility, search algorithms etc. A lot of protocol to be implemented. And the inevitable delays may compromise the vehicle.

They've been at it for years.. and know what they're doing.

Allan

Allanhurst. im interested in your reply. commercially available Rx/Tx pairs. I am guessing you mean there are some commercially available options that include relay points? Never heard of such. Would you mind pointing me in the right direction?

Srnet. I do apologize. I was trying not to be ugly at least.

I meant ordinary rc units for model aircraft control.

But commercial relay systems do exist - microwave point-to-point datalinks - combined with fibre and copper as networks over countries. We rely heavily on them.

Not cheap.

Allan

The more I think about the more it seems that @jgreene33 is looking for an answer that does not exist outside the realms of paid professional advice and expensive commercial equipment - and maybe not even then.

The assumption seems to be that a drone controlled wirelessly from a base station will lose wireless contact due to the presence of obstacles and that having a second ground-based relay unit would solve that problem by providing a different route for the radio signals.

But there is no guarantee that the second ground relay unit would have a clear signal path either without doing tests at a specific location. And that’s without even considering whether the signals from the main unit and the relay unit might interfere with each other.

The mobile phone system has been designed to provide a continuous signal over large geographic areas but even that can be buggered up by obstacles. Think how much fewer resources an amateur has at his/her disposal.

…R