navigation beacons - Page 2 - Electronic Circuits Projects Diagrams Free

**Nigel Goodwin** · 9th December 2007, 06:31 PM

You could have a single sensor, and filter the output through two notch filters, one 2.5KHz and one 4KHz - scan the sensor round in a circle and measure the signal output from each filter as you do - have the sensor in a tube so it gives a fairly narrow angle of detection.

I think I would manually make and test a detection system first, build the beacons as the spec, build a sensor in a tube with filters, and simply move the sensor by hand while monitoring the output from the sensors on a couple of voltmeters (obviously having rectified the outputs first), or use two beams of a double beam scope to monitor the filter outputs directly.

Nice competition rules though, it makes me want to go and build one!

dknguyen · 9th December 2007, 06:38 PM

Quote:

Originally Posted by arod

Competition Rules

I am still left wondering how to differentiate the two signals from each other. Is it as simple as having a phototransistor circuit with a comparator that goes high at a certain threshold. Then I could feed the output of the comparator to an I/O line a microcontroller and check the time that it is high? It just seems a bit too simple to actually work practically.

THe only problem with that (as I mentioned earlier) is I'm not sure what happens if the sensor sees both beacons at the same time, then you end up seeing some strange superimposing of the two (or beat frequencies or whatever). The beacons are probably not synchronized to each other either. You could code it so that if it was a funny reading that wasn't exactly clear cut, you would assume you were reading both beacons at the same time. Simple is good. Try it out. You might be pleasantly suprised.

**Nigel Goodwin** · 9th December 2007, 06:42 PM

Quote:

Originally Posted by dknguyen

THe only problem with that (as I mentioned earlier) is I'm not sure what happens if the sensor sees both beacons at the same time, then you end up seeing some strange superimposing of the two (or beat frequencies or whatever). The beacons are probably not synchronized to each other either. You could code it so that if it was a funny reading that wasn't exactly clear cut, you would assume you were reading both beacons at the same time. Simple is good. Try it out. You might be pleasantly suprised.

Hence my suggestion above - you should also bear in mind that the sensors are a considerable distance apart, in the corners of a closed square, and the robot isn't very far away from them. So with the sensor in a tube (giving a narrow beamwidth) it should be impossible to see both beacons at once (remember the walls are black to minimise reflection).

bobledoux · 9th December 2007, 07:56 PM

Set up a sample beacon and try different reception methods. Assuming each beacon is putting out a square wave,

Read the signal from the beacon on a scope. Create a microcontroller program to count the clock cycles that the signal is high. It should be able to set a pin when the signal is high for that frequency. Some sensors may be able to read the signal without need for further amplification.

If precise angle to beacon is required place two sensors, side by side, with a divider between them. Adjust angle and length of divider so both sensors read the beacon only when the divider is pointing directly at the beacon. This eliminates trying to search for the strongest signal strength using a single sensor.

Test your light barrier materials for opacity to IR. Don't assume on this point.

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9th December 2007, 06:31 PM	(permalink)
Nigel Goodwin	You could have a single sensor, and filter the output through two notch filters, one 2.5KHz and one 4KHz - scan the sensor round in a circle and measure the signal output from each filter as you do - have the sensor in a tube so it gives a fairly narrow angle of detection. I think I would manually make and test a detection system first, build the beacons as the spec, build a sensor in a tube with filters, and simply move the sensor by hand while monitoring the output from the sensors on a couple of voltmeters (obviously having rectified the outputs first), or use two beams of a double beam scope to monitor the filter outputs directly. Nice competition rules though, it makes me want to go and build one! __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

9th December 2007, 07:56 PM	(permalink)
bobledoux	Set up a sample beacon and try different reception methods. Assuming each beacon is putting out a square wave, Read the signal from the beacon on a scope. Create a microcontroller program to count the clock cycles that the signal is high. It should be able to set a pin when the signal is high for that frequency. Some sensors may be able to read the signal without need for further amplification. If precise angle to beacon is required place two sensors, side by side, with a divider between them. Adjust angle and length of divider so both sensors read the beacon only when the divider is pointing directly at the beacon. This eliminates trying to search for the strongest signal strength using a single sensor. Test your light barrier materials for opacity to IR. Don't assume on this point.