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IR Sensor - Signal Strength
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Joined: Thu Nov 03, 2011 7:41 pm
Posts: 4
IR Sensor - Signal Strength
Hello,
I am working on a system that lets us go to an IR beacon, we already have movement down but I am having trouble trying to figure out how to read the ir beacon signal strength. I want to use the signal strength so we can figure out how close we are to the beacon. Any help would be appreciated.

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Thu Nov 03, 2011 7:49 pm
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Joined: Sun Nov 15, 2009 5:46 am
Posts: 1523
Re: IR Sensor - Signal Strength
I am not sure you can reliably use the signal strength to tell how close you are. The signal strength has a lot of variables such as the battery strength of the IR beacon, the amount of IR interference in the room. You are better off using other sensors to determine how close such as the sonar sensor. Even with two IR seekers, you can do triangulation with them.

Thu Nov 03, 2011 10:20 pm
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Joined: Thu Nov 03, 2011 7:41 pm
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Re: IR Sensor - Signal Strength
 MHTS wrote:I am not sure you can reliably use the signal strength to tell how close you are. The signal strength has a lot of variables such as the battery strength of the IR beacon, the amount of IR interference in the room. You are better off using other sensors to determine how close such as the sonar sensor. Even with two IR seekers, you can do triangulation with them.

We downloaded the latest RobotC Driver Suite and that solved our problem. We are using the signal strength for telling the robot when it is close enough to end it's autonomous stage.

We were thinking we could have a config mode where we hold the robot in front of the sensor and get the reading at a certain distance from the sensor so we can be able to judge distance without having to manually update the code based on the signal strength that can be different due to batteries.

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Thu Nov 10, 2011 9:38 pm

Joined: Wed Mar 05, 2008 8:14 am
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Location: Rotterdam, The Netherlands
Re: IR Sensor - Signal Strength
You could compensate for the battery level if you code it that way. It is possible to read the immediate and average battery levels using intrinsic variables.
 Code:nAvgBatteryLevelnImmediateBatteryLevel

Don't ask me how it would work, though I am also not sure if would be necessary since most HiTechnic sensors work internally at a 3V3 level, so they may step down the 4V5-4V8, which would pretty much eliminate the dips you'd see with an analogue sensor.

- Xander

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Fri Nov 11, 2011 2:19 am
Guru

Joined: Sun Nov 15, 2009 5:46 am
Posts: 1523
Re: IR Sensor - Signal Strength
No, that's not the NXT battery you would worry about. It's the 9V battery in the IR beacon. If that battery is weak, the IR signal it generated will be weak. There is no way for the robot to know whether a weak IR signal is because it's too far away or if the beacon battery is weak without calibration.

Fri Nov 11, 2011 4:18 am

Joined: Wed Mar 05, 2008 8:14 am
Posts: 3654
Location: Rotterdam, The Netherlands
Re: IR Sensor - Signal Strength
I am pretty sure those beacons use a voltage regulator of some kind. Running 9V through one of those IR LEDs is sure to kill it quickly

- Xander

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| Professional Conduit of Reasonableness
| (Title bestowed upon on the 8th day of November, 2013)
| My Blog: I'd Rather Be Building Robots
| ROBOTC 3rd Party Driver Suite: [Project Page]

Fri Nov 11, 2011 4:22 am
Rookie

Joined: Thu Nov 03, 2011 7:41 pm
Posts: 4
Re: IR Sensor - Signal Strength
We just decided to make a calibration program that we run with the robot right where we want it to stop and then whenever autonomous is run it reads that the calibrated value and stops there. We are unsure if we will be able to do this during the competition but at least we have a quick way to adjust things when we get on the real field.

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Programmer for FTC team 4250 & FRC team 3660

Sat Nov 12, 2011 10:00 pm
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