Multiple Transmitter to one receiver connection (wireless). BT, RF, Others?

Hey,

I am searching for a possibility to send multiple simple sensor-values.
There are 10 Transmitter, each one is connected to a sensor (FSR 402). I have to receive all those values by just one receiver. At nearly the same Time…

The question is, what to use?

RF-modules can not receive multiple values at the same time, right?

Is BT a option? If yes, which type of module would be good(HM-11)?

Is there another possibility the get there?

Thanks!

No wireless system can receive more than one message at a time on a single frequency. However if the individual messages are very short the interval between messages can be very short by human standards and appear simultaneous.

You need to provide a lot more information.

  • I believe the FSR-402 is a force sensing resistor - is that correct?
  • What distance must the wireless operate over?
  • How often will each device send a message?
  • What will the master need to do with each message when it is received?
  • Will the slave units be mains powered, or will they be battery powered and need to be abstemious with the energy they consume?

Have a look at this Simple nRF24L01+ Tutorial

…R

Yes it is the fsr-402 Force Sensing resistor.

The distance is ca. 10 Meter.

They have to send their values for about 5sec. In min. 500ms interval. (Each)

The master just have to get the values(numbers).

They have to be Battery powered (3.7v lipo?!) Low energy consumption whould be Great.

I’ll Take a look!

Thanks for the quick response!

Bluetooth has a master-slave topology and there can be multiple slaves communicating with a single master, which seems to fit your need. I believe, however, that there is a limit to the number of slaves that can be attached to a single master (7?) and that is less than the 10 you indicate up thread.

The nRF24L01 radios are also supposed to be capable of multi-node networks, but I believe they have a similar limit to the number of nodes in a single net (6?).

One way to get around this would be to have multiple networks bridged together somehow. For example, the master station could have two bluetooth master nodes (two physical radios) each connected to five slave nodes to get to your ten node requirement. This would imply a processor at the master node with at least two serial ports. It's not particularly elegant, but it ought to work for low data rate networks.

Interesting project!
Do you care if one sensor value is never sent or is sent corrupted? Do you need to know which sensor is not sending or sending corrupted values?

What action should the receiver take if any of the above happens?

Paul

@MrMark

Oh okay.. is it possible to use the bluetooth port(s) from a computer/imac? (maybe they can take more slaves?)

Otherwise 2 master on one arduino uno, using SoftwareSerial.h could work?

Thank you very much!

That would be okay as long as the time between a successful transmission and a non-successful is less than 1 sec (even better 500ms).

in case of corruption the value should get deleted or ignored..
if there is a value missing its not a big deal

Ribertee:
@MrMark

Oh okay.. is it possible to use the bluetooth port(s) from a computer/imac? (maybe they can take more slaves?)

Otherwise 2 master on one arduino uno, using SoftwareSerial.h could work?

My understanding is that the 7 slaves per master limit is fundamental to Bluetooth and is going to be an issue with any master.

Software Serial has some limitations, but using one channel of Software Serial simultaneously with the hardware serial channel seems like the fundamental use case, so I expect it would work.

Ribertee:
They have to be Battery powered (3.7v lipo?!) Low energy consumption whould be Great.

In my tutorial there is an example showing 2 slaves communicating with 1 master and that could easily be extended to 10 slaves.

However it assumes that the slaves are awake all of the time which puts a drain on a battery and you have not said how long you want the battery to last between charges or what size (mAh) battery you propose to use.

If you need a very long battery life then your slaves need to sleep for most of the time and only wake up for a few millisecs to collect a value and transmit it. The problem with that scenario is that two or more slaves may send at the same time so that both messages are corrupted. It is possible to write a program to deal with that, but it is not a trivial problem. Simply using the auto-retry system on the nRF24 can actually make the problem worse.

At the moment you have not told us anything about the overall project you are trying to implement. If you do you are likely to get much better advice.

...R

I would suggest one always listening hub-nrf with many nrf-nodes sending to the hub address.

If there is no need for a communication to the nodes, they do not even need a personal pipe address.

So there are 10 handheld devices. Those devices are about 5x5x2 cm.

Each one is connected to two fsr-402 Force Sensing resistors.

If one sensor gets a defined value the transmission have to start for about 5 sec. (min. 500ms interval each) and then stop. This happens at nearly the same time. People get a signal and then they have to – more or less – immediately press one fsr-402.

The distance is around 10 Meter.

The battery should last at least 30min in total (more would be great). I thought about 240mAh Lipo 3.7V but didn't calculated it by now.

The master is connected to a computer and just has to get those values.

With this setup it would be better to poll the stations (the way Robin2 likes it ;)).

You will not be able to read all stations at the exact same time.

If you want to detect "who pressed first", you could synchronize timestamps between the nodes
and read timestamped events detected in the nodes and not (nearly) current raw readings.

Ribertee:
The battery should last at least 30min in total (more would be great). I thought about 240mAh Lipo 3.7V but didn't calculated it by now.

I built some hand-held units for my model railway club. They are powered by 2xAA alkaline cells and the original cheap cells must have lasted at least 30 hours without any attempt at energy saving logic.

Using the AA cells has the advantage that the 3v output is below the max of 3.6v for the nRF24s.

You need to explain in more detail what is to happen when they "start for about 5 sec. (min. 500ms interval each) ". What will be happening during that period?

...R

@Whandall

It's not necessary to detect who was first but if it simplifies the polling (by defining the transmission order)? I think it would be a good opportunity.

@Robin2

The problem with the AA cells is, that they are to big. My handheld devices got quite a flat design.
Could a coin cell 3v like this "CR2032 MFR" work, in any way?

http://www.renata.com/fileadmin/downloads/productsheets/lithium/3V_lithium/CR2032MFR_v04.pdf

In that period each device has to read the frs-402 value continuously or in the same interval like the transmission-rate and transmit those to the master in min. 500ms interval (because of the interferences between multiple devices).

Sorry for the bad information management...

Ribertee:
The problem with the AA cells is, that they are to big. My handheld devices got quite a flat design.

Maybe you need to change the design :slight_smile:
What about AAA cells?

Could a coin cell 3v like this “CR2032 MFR” work, in any way?

I don’t know. I think the problem with coin cells is that they cannot produce high currents

In that period each device has to read the frs-402 value continuously or in the same interval like the transmission-rate and transmit those to the master in min. 500ms interval (because of the interferences between multiple devices).

“continuously” is meaningless. How many readings per second do you need
“because of interferences” seems to me to be putting the cart before the horse. You have no idea yet whether there will be any interference. And if there is it must be managed with a more sophisticated system than flooding the airwaves with messages.

Tell us what you are trying to make. At the moment this is just another XY problem

…R