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Detect angle between 2 devices


New member
Jan 9, 2014
I'm hoping you experienced Robot and Laser builders can help me with some brainstorming for a new project. I need to turn a "robot" to face a human. The human could be carrying an iPhone with GPS, ultrasonic sensor, laser reflector, anything small. Within 15-30 degrees would be close enough. I also need to calculate distance, that's the easy part. So they will already be carrying an ultrasonic device to repeat back the ping. GPS is not good enough because they may be less than 30 feet apart. At larger distances this may be the best solution. I have tried a laser on a stepper, this works so long as there is a Retroreflector mounted on the human. The device below has a stronger signal when pointed within 15 degrees. Is that the simplest solution? The range is not enough with a passive reflector. What range would I get with another ultrasonic device to ping back?

HC-SR04 Ultrasonic Sensor | Let's Make Robots!
Retroreflector - Wikipedia, the free encyclopedia

How about 2 IR sensors with a wall between them? A stepper to turn it until both are equal? What are the pros and cons for this method? Range?

If there were an accurate (100us) clock synched on both ends a laser could scan back and forth. All that is needed is the time of the received beam to calculate the relative angle. I can easily implement the clock part.

Since this is a Laser Forum, let's limit our ideas to those involving Lasers. I included my additional thoughts as background so you can see where I'm coming from. Ideas anyone? Let's Brainstorm together!

This is a device that will be used by Homeland Security to fight terrorism, any good ideas will get credit in my code and a chance to see our product in Action! This is a new project for me, so ideas are sure to come quickly.