Radio based distance alarm for two motorcycles.

Hi,

I'm trying to make an alarm that will trigger when two motorcycles get separated. It's basically so that if two bikers are riding together, and the one behind gets separated (by traffic lights, stopping for a photo, puncture etc) then the leading bike has a buzzer triggered to let them know to either pull over or turn around to find them.

I'm just wondering if anyone knows of a good radio system to use for this? bluetooth seems to have a very easy to use RSSI interface that can trigger an alarm when the signal strength goes below a preset level, but 433mhz modules will have better range and penetration of vegetation and obstacles. Any advice is greatly appreciated.

and I'm not bothered about calculating distance, I just want to be able to trigger an alarm if the two modules get seperated. Of course there might be complications determining the difference between being 200m apart in a city, and 500m in open space, but some tuning of code might be possible to help this.

Anyway, thanks for your help.

AFAIK, BT is good for 10m, unlikely reach the distance of the other side of the road. 433 MHz i 'd think is what you need, modern chip supports digital encoding plus RSSI as well, look Si4432 or Si4463.

From what I have read RSSI is a very unreliable indicator of distance as it can be affected by the environment. You would need to experiment to see if it is suitable for your application.

Rather than using RSSI you could set up a system that continuously sends short messages between the two devices. If the stream of messages stops someone should do something. However it may not really be any better.

I think the most reliable approach would be to exchange GPS positions between the two bikes and have the Arduino work out the distance between the bikes. But that depends on "long range" wireless comms - so you may be back to the previous paragraph.

It would seem much simpler to have the less experienced rider to stay in front.

...R

Thanks guys,

It seems to me that getting a vaguely reliable measure of distance from RSSI or similar will be very difficult and or so prone to errors that it won't work.

Both arduinos will have GPS, so maybe a proper RF comms link with GPS info transmitted will be best then. It could also give bearing information which is cool and very usefull.

I'm just looking into different modules to use now, the SI4432 looks good and cheap but I'm not sure if my coding is good enough to use it. I'm looking at xbee's as an alternative if the price is right. Does anyone know how well the signal travels through obstacles? The 6 mile range look superb, but I wonder how well it'll deal with buildings and trees.

How will you know if your colleague is on the other side of a dual-carriageway hidden by trees in the central reservation but ony 50 metres away ?

...R

how about using a walkie talkie with helmet headsets.

Boardburner2:
how about using a walkie talkie with helmet headsets.

This is what I use for both on-road and off-road. The added benefit is to be able to "chat" with the other rider(s)...

I do understand what the OP was trying to accomplish and do recognize the benefit of having a simple "alarm" to indicate that you're leaving someone behind. I'll follow this thread to see if you come up with anything...

I get it, have used similar in a car (convoy) rubber duck.

Online tracking apps on smartphones works.

I suppose what is needed is something like a mega ADK to talk to the phone and calculate the distance.

Can be used to follow at a distance, so if you cheat on your missus remember to turn off your gps.
:o

Boardburner2:
how about using a walkie talkie with helmet headsets.

We already have that, but this device is more of a fail safe that will always be on. Say when riding through very busy streets, or the person is already on a phone call etc. I'm currently trying to find 433 radios that have a decent range. 2.4ghz seems to be prone to too much interference from objects. The SI4463 seems okay, but I'm trying to determine it's actual range, lots of vendors claim different things.

I now think the best method will be 2 gps enabled arduinos communicating their gps positions to each other and calculating distance and bearing.

now If I can just find a long range and easy to use 433 solution (needed to be legal worldwide)

:o

dave_sausages:
The 6 mile range look superb, but I wonder how well it'll deal with buildings and trees.

Have you considered using GPRS.

The costs of worldwide sim card coverage and the loss of reception means it wouldn’t work for us.

dave_sausages:
now If I can just find a long range and easy to use 433 solution (needed to be legal worldwide)

If you want it to be legal in the US i think the owners will need a licence.

Boardburner2:
If you want it to be legal in the US i think the owners will need a licence.

433mhz can be used without licence upto certain powers and certain durations. According to

http://forum.arduino.cc/index.php?topic=246253.0 I can use

"For Maximum 1 second duration, for period transmission (wait time 30 times of transmission time) ----- maximum 5,000 micro volt/m at 3 meter distance"

dave_sausages:
433mhz can be used without licence upto certain powers and certain durations. According to

http://forum.arduino.cc/index.php?topic=246253.0 I can use

"For Maximum 1 second duration, for period transmission (wait time 30 times of transmission time) ----- maximum 5,000 micro volt/m at 3 meter distance"

Check the powers .

In the US higher powers can only be used by licensed amateurs and they could interfere.

From memory i think you may be limited to 10 milliwatts.
I doubt thats enough for your requirements.
That link is more than 6 months old, stuff changes.

Lots here i think ignore some regs.

If you want to sell the device i suspect you will need a lawyer.

dave_sausages:
The costs of worldwide sim card coverage and the loss of reception means it wouldn't work for us.

You do not need a sim card to use GPS.

Grumpy_Mike:
You do not need a sim card to use GPS.

But you do to use GPRS, as per the comment I was replying to.

Boardburner2:
Check the powers .

In the US higher powers can only be used by licensed amateurs and they could interfere.

From memory i think you may be limited to 10 milliwatts.
I doubt thats enough for your requirements.
That link is more than 6 months old, stuff changes.

Lots here i think ignore some regs.

If you want to sell the device i suspect you will need a lawyer.

Agreed on most points. For the moment I'm assuming that a 433mhz module sold in the U.S. Will be legal in the U.S.

This project won't be on sale, but I'd like to stay vaguely legal.

dave_sausages:
But you do to use GPRS, as per the comment I was replying to.

Yes but you can use GPS and a legal transmitter.
How about this system:-
Long range radio coms 20 Miles open space 1.2 miles urban ( through buildings )

Grumpy_Mike:
Yes but you can use GPS and a legal transmitter.
How about this system:-
Long range radio coms 20 Miles open space 1.2 miles urban ( through buildings )
http://www.wireless-solutions.de/products/long-range-radio
http://www.cooking-hacks.com/documentation/tutorials/extreme-range-lora-sx1272-module-shield-arduino-raspberry-pi-intel-galileo

Great minds think alike (I’d decided on that in a previous comment). I found those modules earlier today, but then I discovered that they’re 45 Euro each! Which put them out of the feasible price range. I’m not expecting dirt cheap, but compared to a 2EUR 433 module, it’s a bit much. It’s a shame though, because they’re perfect otherwise.

As the waters are becoming really clouded when I discover a 433mhz LORA radio on ebay http://www.ebay.com/itm/Arduino-433MHz-LoRa-SX1278

My guess is that module either uses the LORA tech but at a legal power level on 433MHZ, or the same thing except with an illegal power level.

There must be a decent range legal radio out there that's not too expensive, surely?