I am very new here, to the forums and .Net Gadgeteer. So, pardon any mistakes.
I am looking to create a kit with a transmitter-sensor pair, where the transmitter is on a moving object and the sensor can detect the direction of the transmitter. Bluetooth would be idea. But, if that is not possible, then I can certainly switch to other wireless options. And the distances are less than 100 feet, about the size of a small backyard.
I looked in cricket (http://cricket.csail.mit.edu/) and want to create something on the lines, may not be as complicated and involved as that. Moreover, using RF and ultrasonic works to give a sense of the distance between transmitter and receiver but not the direction.
I was thinking of having a sensor that does a sweep (similar to radar sweep) of the surrounding to detect the direction of the transmitter. Another alternative is to receivers along a circle, and the transmitter that receives the strongest signal is directed towards the transmitter.
Is either one a good approach? Are there better options? And how do I go about implementing it? Being a software programmer, I am good with writing the code and not necessarily picking the right components. Any help is appreciated.
Thanks,
Prashanth.
PS: I checked the forums to see whether a similar question was posted earlier. But, I couldn’t find any. There is one (http://www.tinyclr.com/forum/topic?id=8353&page=1), which is pretty close to what I need.
Sweeping an antenna COULD be done, but getting an antenna with a tight enough beam will be a problem. If the beam is too wide then you can’t pinpoint the direction.
A minimum of 3 receivers can be used. They should output the signal strength of the received signal.
Put the transmitter in the exact center and calibrate the receivers. Then you can use triangulation and use the signal strength of the 3 receivers to calculate the exact position.
I think you can use zigbee modules in a mesh network. I thought the protocol lets you request signal strength of other nodes, but I can be wrong.
@ GMod(Errol) - Thanks for the response. With the sweeping antenna, I don’t have to pinpoint. As long as it is in the general direction, that will work for me. If you imagine Roomba having the transmitter, the sensor has to have the general direction of the path the Roomba took. It can be within 3 feet. I can’t use GPS as this kit has to work indoors. Can you recommend any such antenna and transmitter, especially one for which I can write some programs.
About the multiple receivers, I realize the mistake in my sentence. It should have been “Another alternative is to receivers along a circle, and the receiver that receives the strongest signal is directed towards the transmitter.” See the image attached, it might help. Here, 1 will receive the strongest signals from the direction of 11:00 O clock or the top left corner, 2 from 10:00 O clock, 3 from 9:00 O clock, and so on.
@ WouterH - Thanks for your help. Ideally, I’d like to avoid triangulation. But, if that’s the only choice, then so be it. Could you recommend any such modules that I can use? And how do I go about programming them? I have zero knowledge of the electronic components. So, any help would be greatly appreciated.
Then you can use the similar technique your wlan interface with 2 or more antennas uses. You place 3 antennas at 10cm from each other. The transmitter sends a fixed frequency. The 3 receivers all pick up the same signal. You can’t compare signal strength because that would never be accurate enough. But you can compare the phase of the received signal. F.e. Wlan sends out a signal on 2 antennas with the same phase shift as the received signal, so the signal that travels to the other end will have more power (because the 2 transmitted signals will overlap).
Note that this is designed for 144MHz. It will not work for 2.4GHz. The pcb and, possiblely the RF, will need major rework to get the impedance back to 50 ohm…
@ WouterH - I lost you after “But you can compare the phase of the received signal.” Also, I read the wiki article a few days ago. But, I didn’t know where to start with that … as in how do I go about finding out the right components, getting them, and programming them.
I think I will use the approach mentioned here N Female Bulkhead w/ 2.4GHz Radiator (Cantenna Type) – JEFA Tech. I will try it out with wi-fi first, and if it works, try it with bluetooth. Now, I have to collect parts to get the transmitter and the receiver right.
@ EriSan500 (Eric) - That’s a good idea, each sensor could use a 3 axis mag and an xbee or BT to send it’s orientation back to the master and it knows it’s orientation and then simple maths and it’s “Bob’s your uncle Fanny’s your aunt”
That would give you the direction one node is pointing, but not the relative direction between the nodes. Ie, all nodes can point north, which the compass gives you, but the nodes can be next to each other, so the direction between them are east/west…