Let's Make Robots!

Sensor Ideas

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 This came out of a toy that was a monkey with rubber arms. When you shot him like a slingshot he screamed louder than the sound of millions of people burning in errr umm Heck.

I wondered what made the jarring motion set the screaming off and tore one of them apart (it was annoying my parents when my nieces played with it at her house). That circular part is the sensor that makes the jarring motion of him flying set the sound off. It is a circular piece of metal with a spring inside. When jarred the spring touches the metal part and for an instant completes the circuit which starts the yelling until the sound file has been played fully.

This got me to thinking. What other cheap sensor ideas could be home made for cheap? I thought about using this sensor for a robot pet. When it ran into something (the sensor didn;t tell it to stop) it stops makes a noise and does an about face. Or maybe this detects when it is picked up or moved.

Anyone else got some home made sensor designs? Either a sensor that already exists, but can be made for cheaper, or a sensor that you made up on your own. If I can think of a prize I may make this a contest...

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robologist's picture

There was mention of using piezo transducers here by clcheunghk for acceleration sensing with amplification.

Another hack I'd heard was in taking the top off of old CMOS memory, and using it's light sensitivity as a camera of sorts.

All I've done has been simplee switches out of piano wire

There used to be a product called sensor paint, that the manufacturer got worried about it's possible misuse. Think it might have been graphite suspended is some rubbery elastomer. 

And the encoders from ball mice. And the ultrasonic transducers and drivers from some old Polaroid cameras.

The ThereminVision was something that might be interesting to try out. Think there was automotive sensor like this, to tell if people were in the seat or not.

OddBot's picture
Thanks for the links Robologist, I've mentioned elsewhere about capacitive sensors and gave the stud finder as an example. I'm going to give this one a go since its so easy to make. (if I get the time, you know how it is).
anachrocomputer's picture

There's a commericial sensor (maybe made by Sharp) that's a tiny plastic box with a plastic bead or ball inside it.  The ball breaks an infra-red beam inside the box, making it a shake or tilt sensor.  Some digital cameras use them for sensing a "portrait" or vertically-oriented shot.  You could make something similar with a swinging pendulum that breaks the beam in a standard opto-slot (photo-interruptor) sensor.

Meanwhile, I'm working on a rotary encoder based on the three hall-effect sensors in a CD-ROM motor (brushless DC motor).  It's working OK so far, counting up when turned clockwise and down when turned anti-clockwise.It's a 32-bit counter, implemented in software on an AVR chip.

 

OddBot's picture
Have you got a use in mind for your brushless motor/rotary encoder?
anachrocomputer's picture

At the moment, the CD motor/rotary encoder is just an idea with no particular application in mind.  I was inspired by a posting on the Make magazine blog:

 http://blog.makezine.com/archive/2008/11/hddj_hard_disk_for_rotary.html

But I didn't have the right kind of HD motor!  So I suppose it could be used for musical instrument control, as that article suggests.

 

OddBot's picture
I've posted a walkthroughs on home made force sensing resistors using antistatic foam.
Zanthess's picture

I just have to say I freaking hate those monkeys. My mom owns a salon and would sell them by the dozens, and just HAD to show how they worked to every customer that came in.

I never thought to take one apart though. Thanks for sharing a picture of the insides! :) 

jklug80's picture
I left it at work, but it is VERY simple. The chip where the sound is strored is just a black plastic bump. I was hoping for something I could reuse.
OddBot's picture

Get an old pen, cut off the end so you have a short length of plastic tube about 10-15mm (half inch) with a sealed end. Drill two very small holes in the sealed end and insert two wires. Supa glue the wires so they don't come out. Put a small ball bearing in the other end thats big enough to touch both wires, this acts like the mercury. Seal the open end with hot melt glue being careful not to glue the ball bearing.

When the wires are downward, the ball bearing shorts them. Tilt it with the wires up and the ball rolls away from the wires.

fritsl's picture

I bought a sandwich and got a step-counter for free the other day. Strange thing was that I had to buy a menu (including fries, that is) to get the "helthy option" with a free step-counter ;)

Anyway, of course I took it apart, and saw that it had like a stick of flat metal with a hole in one end. In the hole was a plastic pin, so it could swing like a door-handle.

Gravity (and other pins holdig it in place) would make it rest on a piece of metal, making contact. However.. a rather long springey and bend piece of metal held it just above the switch.

Walking would make it click down all the time.

Will get a picture of it, I hope to remember, I am somewhere else now :) 

Use? Well.. erh.. it's a sensor!