A Day at the Museum

Hi all,

New to the Forum and Arduinos in general, but have previously been a "dabbler" in hobby electronics before. My current project I'm working on is to trigger an led display within a museum glass case preferably by someone standing on the outside looking at the exihibit. I dont want to press a switch, but thought I could use some kind of proximity detector or reflecting IR led - trouble is it must all be behind the plate glass. Any ideas on a sensor I could use to trigger the arduino ?

A microwave motion detector should work.

PIR motion sensors are very inexpensive, small and easy to program in your sketch and hook up to your arduino.

I like to use microduino components since they are so small and easy to use. They have a series of stackable modules that are called mCookies which use magnetic pads in place of pins which are easy to put together. I do prefer the more traditional of stackable modules but I have snapped of a few pins since they are so tiny to see.

For this project, you would get

  1. CoreUSB $16
  2. Sensor Hub $8
  3. PIR Sensor $6

https://www.microduino.cc/store

jremington:
A microwave motion detector should work.

Quite expensive though! Maybe worth trying a cheap PIR sensor first, there’s a chance it might work through the thick glass on max sensitivity.

s-l1600.jpg

jseery beat me to the suggestion by seconds. I would recommend a nano 3 and the above sensor. Then you have spent only $5 total if it does not work.

You might be able to get by with a much smaller device that works the same way.
motion sensor.jpg

Glass windows are essentially opaque to the long wave thermal radiation (e.g. 10 um) detected by PIR sensors.

jremington: Glass windows are [u]essentially opaque[/u] to the long wave thermal radiation (e.g. 10 um) detected by PIR sensors.

Yeah, that was my concern too. But at one twentieth of the price of that microwave sensor, still worth trying PIR just in case it does work if you turn the sensitivity all the way up.

How about a two-part design? Perhaps you could mount the PIR sensor outside the glass case and wire it to light up a visible led which shines through the glass, directly at an ldr or photo-transistor circuit on the inside of the case. This triggers the led display.

What is the led display? If it is simply illuminating the exhibit, you may not need an Arduino.

My first thoughts ran to a capacitive proximity sensor

Can you use some sort of visible light detection - perhaps the visitor throws a shadow on the exhibit and that could be detected by a Light Dependent Resistor.

...R

The glass is laminated and I was told PIR wouldnt work although I havent tried it. I know my house PIR wont detect through our patio doors. Unfortunately they wont let me drill through the casing. I think Ill give it a go and experiment with it. Perhaps if its very close to the glass it may work !!

Fit a switchmat in front of the case

Allan

Maybe silly idea but what about visible light LED (or UV LED) turned on for very short time - about 1us? Too short for human to notice but long enough for Arduino to “see” it?

Smajdalf:
Maybe silly idea but what about visible light LED (or UV LED) turned on for very short time - about 1us? Too short for human to notice but long enough for Arduino to “see” it?

About 8 microseconds is difficult to observe and easy to detect.