Downhill skating timer ideas needed to start a timer project

Projects General Guidance
1

Hello,
First of all, to gave my level in arduino, I have built successfully a macro linear rail for photography involving DSRL IR control, step motor, joystick and a menu on a 128X64 graphics.

My next project would be to build a track timer for me and my few friends when doing roller skate downhill (less than 10 people)

Goal:
Get on an interface the last timing + best timing for each of us + bonus top 10 ordered list
minimum precision needed is around 2s (but 500ms would be bonus)

Environment:
We are on roads in the montains, no Gsm data available, very low radio noise. only battery energy available.
The track is between 2 and 4km long, with no line of sight between start and finish.
It is important that everything runs automaticaly once the setup made (no need to push any button any time during half a day at minimum)
Not like skiers, we like to overtake each other during the downhill and we also like to start 3-30s delayed.
Speed during start and end is low: 10/20Km/h max (we're going up to 90Km/h in the middle of the track)

The ideas:

Idea 1

Have a passive "beacon" at start, another passive "beacon" at end.
and we carry on us a device that has the inteligence to calculate the timing between start and end.
then each timing is uploaded to a device at end to store and display all our timings during the day

Idea 1 Pro
No need to have communication nor time sync between start and End of the track.
Idea 1 Cons
Need to have a wearable intelligent device.

Idea 2

Have an identified skater detector at start, another identified skater detector at end. get the 2 timing to a device for storing and display

Idea 2 Pro
Depending on technology to detect skaters, maybe very simple device to carry

Idea 2 Cons
Need communication between start and end

Technology:

The UHF RFID used for competition need something on the road + very expensive long distance RFID reader >> going out of budget

The IR technology used on car race timers is difficult: where should we carry the IR emetor/receptor to be sure it activate?

The Bluetooth Beacon seems not very accurate because of the delay of detection (3-5s)?

Wifi beacon seams also not accurate due to the same reason.

Optical detection (using big QR codes on our helmets?) seems difficult to set up

My better idea of technology seems to have radio that emit a known frequency that can be detected (like very old school TV remote, remember?)

for communication between Start and end, Walkie talkies works, so maybe using this kind of frequency could be possible to get a very slow communication in between (we have 3-5 minutes to pass 10 timing variables, no hurry!)

The storage and display can be easily managed once we got the timing values: arduino +SD card + a nice LCD.

Max budget is 300€, maximum 500€ if i can get precision.

Does someone sees technology i could use for idea 1 or idea2?
any toughts welcomed!

thanks very much in advance

2

uharn:
We are on roads in the montains, no Gsm data available,

Interesting project!
You don't need GSM but you could use GPS which is available everywhere outside (though not very good in buildings or under thick trees) with an accuracy of 10 metres or better.
A GPS recorder could record position and time over your course. When downloaded at the end, the software could find the coordinates of the start and end points and do the necessary calculations of speed etc.
20 km/hr about 5 m/s so the GPS accuracy could give you 2 seconds or better.

Although if your budget is for everybody together, not per person, that's too expensive I guess.

3

thanks, Yeah GPS would be an idea, but they work great when the sky is fully open, so in the mountains and often on little road with trees... I tried to record my own GPS traces with my phone few times and they were not good at all...

4

Depends on the app you use (and on the quality of the phone).
Here's a bit of the download from my Strava today:

   <time>2017-02-22T10:01:42Z</time>
</trkpt>
<trkpt lat="50.2636420" lon="-5.0554800">
    <ele>8.0</ele>
    <time>2017-02-22T10:01:43Z</time>

so a new position every second. Writing your own code in an Arduino you could get locations more often.

5

The ceramic resonator used on most arduino's is only accurate to 2% or so.

So whichever way you go, you need a better reference

regards

Allan

6

I do completely agree about the timing issue with the occilator, an RTC will be needed.

I think getting GPS all day long just for Few points at start and few point at stop, is a lot of data for so few usage.

I'm currently looking for RF 433Mhz emettor and receptor to detect start and end (I'll need to tweak the db of the antenna to get 5-6m range, not less, no more)

7

Hello, I have found a very nice device including an RTC and a LoRa transceiver, I'm new to wireless frequencies,
would someone help me how to get a range that is bellow 6 meters? (so i can detect that i'm leaving the beacon zone using RSSI measurement with a correct precision)

which one to choose and why?

  • LoRa RF92W 868Mhz
  • LoRa RF92W 915Mhz
  • LoRa RF95W 868Mhz
  • LoRa RF95W 915Mhz
  • LoRa RF96W 433Mhz
  • LoRa RF98W 433Mhz

I would use the same device for the beacon to be sure that they can communicate

8

Hello, I have found a very nice device including an RTC and a LoRa transceiver, I'm new to wireless frequencies,
would someone help me how to get a range that is bellow 6 meters? (so i can detect that i'm leaving the beacon zone using RSSI measurement with a correct precision)

Frequencies? whatever is approved in your country.

Antennas? you may need yagis to get sufficient signal , particularly in wooded/built-up areas

Otherwise...Not sure exactly what you mean . RSSI is a very poor measure of distance. LoRa is great, but has a significant and unpredictable delay time in transmission/reception. And if you're after 5km range, why would 6 meters be useful? though it would probably work. Why not use some other method? ( optical occlusion - IR emitter/sensor)? Man with a switch?

Suggest you use 2 units, with synchronised RTC clocks, and use the radio link to obtain the start and end times.

Be nice if the RTC modules outputted a 1-Hz pulse , which you could then interpolate with the arduino millis() function. Ho hum

Allan

9

Thanks for your return,

I just want to use the RSSI to be able to detect departure from start time and arrival to end time, that's why i need a "small" range.

That start and end zone will be something like an unprecise circle, but that's ok to me.

I do not want IR because of alignment issues between skater and system
I do not want optical occlusion because we do not know the order of skaters and it can change during downhill.

I now have to look for the best Wireless with RSSI and fast scanning, thanks for your advice on the LorA delay time.
Currently looking at Xbee (the cool things with Xbee is that I can try, if it's KO, i can reuse Xbee modules for domotic systems at home :wink:

I was also more sticking to my IDEA 1 more than on my IDEA2 (see first post) because the communication between start and end is risky and difficult to test at home.

With Idea1, I also only need one time reference on each skater instead of synced time between 5km away start and end.

10

So you want to detect > 6 metre range of each skater at oith start and finish using RSSI....? And report the times with LoRa? What if 2 or more skaters are very close together and transmit at the same time?

There's a lot of protocol involved to sort that out... probably a polling system.

Might work, but the rssi is going to be very imprecise...

Allan

11

Sorry if I was unclear, my idea is to have an arduino + wireless + RTC on each skater.

When a skater quit the start zone (leaving the zone would be detected by loosing signal strengh) the timer start.

when skater enter the end zone (Another strengh signal detected) the timer stop.

then the arduino would use the wireless at the end to upload each skater time to the central timing memory for display.

detecting again the start zone reset the timer and wait until leaving it again

that way of working seems ok to me because the RSSi is only used as something to get a few more precision on the size of the zones.

We can then have fun the whole day without checking anything except our timing on the central display when we want to.

I'm wrong?

12

Have a look at Bluetooth Low Energy, it's range is small so you wouldn't need to measure RSSI, just act on whether or not a signal is present.