Category Archives: Electronics

April Maker Day

Today was maker day for the month of April.  It was snowing and cold outside but toasty warm inside.  Alex and I decided to build catapults.


They came in a kit and required glue and a little time to put together.  Alex did a great job, here is his.  I really like the targets that came in the box.Alex's Catapult and Targets


We will try them out tomorrow after the glue dries.  Maybe even put the stickers on to make them pretty.

After Alex was done he went to watch a movie.  I was still feeling the need to build and when Terri came back from the mail box I had what I needed to finish making today the April Maker Day.

April Maker Day Courtesy of Jameco

Jameco Electronics sends me emails every so often and they usually have something that looks like it would be fun to build.  Last week’s email was Puzzler 17.  Another Forest M. Mims creation.  The basic idea is to build a plant detector.  Is the leaf real or fake?  Is it a green plant or camouflage.  Here is their picture – the teaser.

Fake or Real

Fake or Real

What I love about the Jameco workshop and the teaser emails is that I always learn something while having fun.  I have to give Jameco a big thumbs up here too.  I ordered my parts Friday morning and had them today via standard US Mail shipping.  I couldn’t believe it – but Terri walked in and set the mail down with my package right on top – yea!  Maker Day!

After the puzzzle question is asked there is a solution posted.  When I first read the solution I sat back in my chair and said – “I didn’t know that”.  Light Emitting Diode’s will detect light in the frequency they transmit.  LED’s will generate light when power is applied to them, red, white, green, infrared, and you can use them to detect the same color of light.  On Friday I said to myself, “I must play with this”.  So I ordered the parts list.  a few bucks and an envelope of parts later I have the Artificial Vegetation Detector.



The Red and IR diode pair gets stuffed into a home made collimator or narrow-beam lens. Home made IR - RED Light Detector  I made mine with some cardboard and black shrink tubing. Inside the IR - RED Detector The green plant is supposed to absorb the red light as part of the photosynthesis process and reflect the IR.  When that occurs the green LED turns on.  Green plants are supposed to do work this way and plastic plants should reflect the red light and IR equally.

The detector is connected to TLC272 Operational Amplifier.TLC272 Op Amp


I remember playing around with a Heathkit course that my day had bought – when I was 16.  The Heathkit Op Amp course had me building the transistor circuits – I wish I could remember all that Heathkit told me.  What I know is that the signal coming out of the LED is very weak and it has to be amplified.  So a couple of Op Amp’s do the trick.


April Maker Day – Messy Table – Workbench

Maker Day - Workbench

I get to make a mess out of the table when I do things like this.  My kitchen workbench is a bit messy but it was all part of the fun.  I opened the envelope and put the components onto the bread board.  I made my sensor and then fired it up.  A little spin of the potentiometer adjusted the red light sensitivity and then I could test it.

It is a leaf?


It worked!  Green leaf turns it on.  Plastic just a piece of plastic and it stays off.

I found that my kitchen table light, a plain incandescent bulb worked just as well as the flash light.  The white LED light flash light does not work and I tested that as well just to verify that the LED was working.  It is not as adjustable as I was hoping for.  I think the collimator needs to be smaller at the opening.  The flash light I was using was so bright that it would really light up the target and even the textured black plastic reflected so much light that the sensor would turn on.  Once I started using just the kitchen table light as my full spectrum source the testing worked well and I got the pictures above.

I’ll fess up here – I never remember which lead from an LED is the cathode (-) and which is the anode (+).  So thankfully Google is loaded with good sites and pictures that will explain it.  Sparkfun’s Diode and LED Polarity Tutorial is the best I have seen.

I think for my next maker day I want to build a wireless telegraph using the parts and ideas from this.  I had no idea that LED’s made a good sensor.  Nor did I realize that an incandescent light bulb put out infrared light.  Makes sense, that is what the heat from the bulb is – I just never thought about it. The one improvement I think would be to take the outputs from the red and IR Op Amps and feed it into an NAND gate.  That way when both lights were present it would tun the green LED off.  Hmm, might have to try that too.

Happy April Maker Day!