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The Open Dream Journal Clip

1 Apr

I have wanted to design a simple notebook clip with an LED light for use on a dream journal for quite some time now.  Writing down dreams at night is difficult without a very convenient light source.  Now with access to a MakerBot 3D printer at sprout studios, I’ve released an open dream clip design on thingiverse, an online database of freely available and printable 3D models.  My design uses an LED and CR2032 battery, components commonly available at hackerspaces that would have 3D printers (and radioshack, although the parts are cheaper online through sites like digikey and mouser).

Here is the dream journal clip in action:

Dream Journal Clip with a white LED

Dream Journal Clip with a white LED

The first revision is pretty rough and we had to use tape on it to make it work:

Dream Journal Clip with a red LED

Dream Journal Clip with a red LED

Here is the MakerBot that Jimmie Rodgers kindly tuned and used to print the first test:

MakerBot at Sprout

MakerBot at Sprout

Planned improvements include:

  • using less plastic
  • making a larger hole for seating the LED
  • making a larger and deeper battery slot
  • adding a plastic tab to hold the battery in place (instead of tape)

Download the source files for the open dream clip on thingiverse and keep an eye out for  improvements shortly.

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Soil Moisture Meter with a 555 Timer

5 Feb

For the past two days, I have been thinking about and building a low-cost electronic soil moisture meter for house plants that does not involve using a microcontroller.  To accomplish this, I envisioned being able to blink a light (LED) to indicate when a plant requires water using a cheap 555 timer and two nails to measure soil resistance.

Soil Moisture Sensor based on 555 Timer

Soil Moisture Sensor based on 555 Timer

555 timers determine their output signal based on two resistors and a capacitor.  I used the Astable 555 Square Wave Calculator to determine blink speeds for lighting an LED and for the 555 schematic.  To figure out what my capacitors were rated in Farads, i used the Electrostatic Capacitance Converter to convert uF to F.  My 2.2uF capacitor was 0.0000022F; that’s 2.2 times 10^-6.  I used a 100,000 ohm resistor for R1 and 10 ohm resistor for R2 to achieve a frequency of about 6.56 hz.  It looked like this:

Astable 555 Timer Circuit with Two Resistors

Astable 555 Timer Circuit with Two Resistors

To create a soil moisture meter, I used 2 parallel holes (1 inch apart) in a small piece of wood to put 2 bright common nails with wires attached (with solder) through the holes.  Speaker wire worked well here because it’s flexible, there are two wires within it, and it can easily be split apart.  I then replaced the 10 ohm R2 resistor with my soil moisture meter.

Astable 555 Timer Circuit with One Resistor and Soil Moisture Sensor

Astable 555 Timer Circuit with One Resistor and Soil Moisture Sensor

Here’s a short video of what it looks like in action:

The timing isn’t quite right, but it shows promise as a prototype that can be refined.

Lemon Juice Batteries and Joule Thieves

1 Feb

To kick off February Project Month, I wanted to explore lighting LEDs with small voltages generated by lemons.   By using the evilmadscientist joule thief circuit, one can power a 3 volt LED from sources as low as 0.3 Volts such as dying batteries.   I wondered whether a joule thief could power an LED with low voltages generated by lemon style batteries.  To begin, I created a cleanly packaged design for a copper/foil battery that could reliably read 1V on the voltage meter.

I created an instructable on how to create my 1 Volt Cell from 2 Pennies and Foil.  The design uses dish soap instead of lemon juice which I found intriguing and slower to evaporate.

1V cell measuring 1.2 Volts on a Multimeter
1V cell measuring 1.2 Volts on a Multimeter

I then created my joule thief by following these instructions on How to Make a Joule Thief.  The video shows the entire process of building.

Joule Thief Working with 1.5V Battery

Joule Thief Working with 1.5V Battery. Click for more pictures.

The joule thief worked like a charm for regular batteries generating about 1.5V.  It appears however, that my 1 volt battery design did not source enough current to generate the required 3 volts in the joule thief’s inductor.  This experiment is still far from conclusive however because there are more efficient joule thief designs that utilize capacitors.  I will also try testing a similar penny battery design aimed to generate 1.5 Volts.

Comments and insight are welcome.  Thanks!