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Topic: Echo Detector, object locating device (Read 733 times) previous topic - next topic

wizdum

I have been asked by a airsoft game operator if it is possible to create an "Echo Detector" for a Stalker, Shadow of Chernobyl scenario "cheaply". An echo detector is a device that alerts the player when an "anomaly" is nearby, and beeps more quickly as the player gets closer. So I will need to create both an "anomaly" device and a detector device. The longest range needed is approximately 50 feet (I think, still waiting on this information).

Since I havn't received any specific information about the prop, i'm going to break this into two steps. The first step is just to get the Arduino to detect when it is within about 50 feet of a device. The ideas that immediately come to mind are those cheap RF transmitter/receiver pairs that you can get on ebay for like $2, but i'm not sure of the range. There's going to be a lot of these devices on the field, so I don't want them interfering with eachother. Other options are IR, Bluetooth, and ultrasonic sensors. I don't think I could get GPS modules cheaply enough, or accurate enough for this.

The second step is getting some idea of how far apart the two devices are. The accuracy can be fairly low. If it could just tell the difference between max distance, 2/3 max distance, and 1/3 max distance, that would be good.  To get an idea of the distance, the usual method is to send out a pulse at a known speed and see how long it takes to come back. I don't think the arduino microprocessor is fast enough to do this with RF or IR. Would this be achievable with an ultrasonic transmitter and receiver? I could use the RF pair to sync the time on the two devices, or a realtime clock if that would be accurate enough.  Are there any bluetooth modules that can be queried for signal strength?

I'm probably going to end up building these below cost, so any help is appreciated.
"Anyone who isn't confused really doesn't understand the situation."

Electronic props for Airsoft, paintball, and laser tag -> www.nightscapetech.com

PaulS

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The ideas that immediately come to mind are those cheap RF transmitter/receiver pairs that you can get on ebay for like $2, but i'm not sure of the range.

The range is poor to mediocre, depending on the antenna you create.

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There's going to be a lot of these devices on the field, so I don't want them interfering with eachother.

Then, cheap radios are not the solution.

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Other options are IR, Bluetooth, and ultrasonic sensors.

IR and ultrasonic won't distinguish one device from another. Ultrasonic won't even distinguish between the device, the ground, another player, etc.

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I don't think I could get GPS modules cheaply enough, or accurate enough for this.

I don't either, but, if you do, let me know.

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The second step is getting some idea of how far apart the two devices are.

Good luck with that.

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To get an idea of the distance, the usual method is to send out a pulse at a known speed and see how long it takes to come back.

But, what did it come back reflected off of?

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I don't think the arduino microprocessor is fast enough to do this with RF or IR. Would this be achievable with an ultrasonic transmitter and receiver?

Yes, but see comments above.

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Are there any bluetooth modules that can be queried for signal strength?

Signal strength is a very poor indicator of distance.

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I'm probably going to end up building these below cost

How? Or, did you mean that you will be selling/providing them for less than it costs you to make them?

PeterH


I don't think I could get GPS modules cheaply enough, or accurate enough for this.


I've got a GPS logger that can track down to a couple of feet, but you'd need pretty deep pockets to buy one of these for a game.

The only way I can see this working is for each basestation to broadcast a constant signal and each mobile device detect the presence of the signal - I'm sure there would be ways to get a indication of signal strength, even if it was a crude as switching the antenna.

The problem with this approach is that signal strength gives a very poor indication of range and the signal will come and come seemingly-arbitrarily as you approach the source. Maybe you could exploit that as part of the fun - if not, I don't think any RF detection based approach will work, and I don't see any practical alternatives.
I only provide help via the forum - please do not contact me for private consultancy.

sbright33

How about a combination of RF and ultrasonic?  RF will go on and off around 50ft unreliably.  Sound will show when you're within 20ft.  Less than that you can use the ping (sound) idea?
If you fall... I'll be there for you!
-Floor

Skype Brighteyes3333
(262) 696-9619

wizdum

#4
Jun 11, 2013, 04:18 am Last Edit: Jun 11, 2013, 04:33 am by wizdum Reason: 1

How about a combination of RF and ultrasonic?  RF will go on and off around 50ft unreliably.  Sound will show when you're within 20ft.  Less than that you can use the ping (sound) idea?


That might work. I was wondering if there was a way to use a separate ultrasonic sensor and transmitter. That way the "anomaly" is just an ultrasonic beacon, and the detector picks up the pings from it. A traditional ultrasonic rangefinder wouldn't work because theres no way to know what the sound is bouncing off of. Thats why I was thinking of using a separate transmitter and detector, and using either a RTC module or RF "packet" to sync the time between them. Ben heck did something like that for the luggage that follows you: http://www.youtube.com/watch?v=tAyWrJoVUbs

The player doesn't need to be able to differentiate between anomalies, they just need to know that there is one "nearby". If those RF modules have poor range, that would be perfect. The anomalies will be static, and placed by refs, so they will be set a few hundred feet apart, or more. The anomalies will also most likely be separated by some pretty RF hostile territory (thick trees, brush, swamp), but the detectors will be in the same clearing as the anomaly.

How would I get different range from different antennas? Would it be as simple as having an antenna outside the detector's box that could pick up the anomalies from much farther, and one inside the box that would only work at closer ranges?

Anomalies are areas where "the laws of nature and physics have been corrupted", so I imagine a little inconsistency would be expected. http://stalker.wikia.com/wiki/Anomaly

What I mean by "below cost" is that I will be partially compensated for the hardware costs of this project. I usually build props for profit, but this is for a local field that I like to help out.
"Anyone who isn't confused really doesn't understand the situation."

Electronic props for Airsoft, paintball, and laser tag -> www.nightscapetech.com

sbright33

If you use the PPS pin from a cheap GPS, then you no longer have to Ping both directions or round trip.  If all the units are in sync, you only need to go one way from transmitter to receiver.  The time difference will give you an accurate distance.  This time measurement is SO accurate you can almost do it with light or radio speeds.  Sounds can be accurate to inches, or the time between peaks of the sine wave.
If you fall... I'll be there for you!
-Floor

Skype Brighteyes3333
(262) 696-9619

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