Halloween Forum banner

1 - 8 of 8 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter #1
Hi. From time to time I think about how cool it could be to have a prop watch TOTs as they walk by, but I don’t know how to do this.

I suppose tracking sound with an array of microphones might work.but I can easily imagine such a system being easily distracted.

I’ve heard of approaches in which a light source shines toward the prop and a bridge of photoresistors is used to create an X and Y error voltage. The drive mechanism steers the photoresistor array in a continuous effort to balance the bridge error voltages in the shadow..

Another possibility might be to make a bridge of passive body heat infrared sensors so that it’s not necessary to illuminate the TOTs to create a shadow for the sensor bridge to track,

Has anyone successfully implemented a motion tracking system, and if so, how?

Thanks!
 

·
Registered
Joined
·
3,425 Posts
This can be done with multiple PIR's and a microcontroller but writing code for this is a bit on the advanced scale. The other issue is that there will likely be TOTs in the field of view of all the PIR's simultaneously which would pretty much kill the effect.
 

·
Registered
Joined
·
350 Posts
A simpler approach is to create the eyeballs as a concave shape. This creates the illusion that the eye is following you. I could not find anything that shows exactly how to do this bu here is an article shows an example:

 

·
Registered
Joined
·
38 Posts
Discussion Starter #4
J-Man, I hadn’t thought of experimenting with multiple PIRs, but it sounds like a promising approach. I see your point about the system getting “confused” by multiple sensors detecting motion at the same time. Perhaps under those circumstances the microcontroller could make the prop cycle it’s gaze among the stimulates sensors.

JW, thanks for posting the link about the robot that makes people feel like it’s staring at them. It sounds similar to the method used by the “gaze-following” statues in Disney’s Haunted Mansion.
 

·
Registered
Joined
·
20 Posts
Thanks for posting this Buckwitch, as I have been thinking about a similar type of project. In my research, I found this on youtube which seems a similar approach to the PIRs that J-Man suggests. I just haven't tried it yet.

 

·
Registered
Joined
·
38 Posts
Discussion Starter #6
Thanks for pointing out the video, CaptainLlama. It’s always interesting to see how different creative people approach the same challenge.

While the “Which sensor is in the darkest shadow?” approach gets the job done, it appears to rely on bathing the prop area in sufficient light such that TOTs will be walking between the light source and the various photoresistors. Also, I haven’t checked the code to see if the Arduino program interpolates the voltages from each photoresistor to more accurately steer the skull, or does it just point the skull toward the sensor in the darkest shadow.

I’d like to try something similar if I can find PIR modules with analog (vs. digital) sensor outputs so I can make the prop movements more continuous.
 

·
Registered
Joined
·
38 Posts
Discussion Starter #8
Doesn't look like interpolation from the video. Seem like fixed angle for each photoresistor.
I agree.

While looking around for IR sensors with analog outputs I came across Panasonic’s “Grid-EYE” series of 8 by 8 IR element sensor devices. Digi-Key sells them for $29.10 ea. and lists them as “obsolete”. I don’t know if that means that a new replacement is (or will be) available.

After watching Sparkfun.com’s short demonstration video for a breakout board they sell ($41) using one of these devices, I ordered one to play with. Sparkfun demonstrated how they used an Arduino connected to their breakout board to drive an 8 by 8 array of RGB LEDs to produce a low-resolution IR image of a hand waving across the sensor’s field of view. Very cool!

I’m no software wiz, but I suspect there’s a way to read the sensor’s data to steer a prop (upon which the sensor has been attached) to face a hot spot (e.g. driving pan and tilt servos to center the brightest area of the image within the sensor array’s field of view). If there are multiple “TOT hot spots” in view as J-Man mentioned, the servos could be driven to either make the prop face the center of the group or to cycle its gaze to each individual hot spot.

Other stuff prevents me from playing with this project idea soon, but I wanted to share this sensor information in case others want to begin developing ideas and experimenting with these (or perhaps other similar) IR array sensors for their props.

Fun stuff, eh? 🙂
 
1 - 8 of 8 Posts
Top