Miscellaneous Projects

 

1.     A Treasure Box that can light up your diamonds

2.    Home made Seismograph for classroom demonstration

3.    LED Flashlight Mod

 

A Treasure Box That Can Light Up Your Diamonds

 

Materials List

Qty Description
1 Wood treasure box (5"x3.5"x3")
2 Cassette cases
4 AA batteries
6 White LEDs
1 NPN transistor Ic>500mA (I used 2N2219A)
1 15K 1/2W 5% resistor
4" Copper sheet 0.015" thick, 0.5" wide
24" 22AWG hookup wire
4 sets #5 0.5" screw and nut
1 insulation sheet 0.5"x0.5"
around 100

Acrylic diamonds (Of course you can use genuine diamonds)

 

Assembling the battery pack

  1. Make 2 pieces of terminal plate as followings.  Install one of them into one end of a cassette case.

  1. Make another terminal plate by cutting 0.5" of copper sheet.
  2. Solder a 4" hook-up wire to them as shown below. 

  1. Attach an insulation sheet to the bigger terminal with double-sided tape.

  1. Attach the smaller terminal plate onto the insulation sheet with double-sided tape.

  1. Install the terminal plate assembly to another end of a cassette case. 

The completed battery pack.

 

Make the lock a switch

  1. Replace the wood screws with #5 screws.
  2. Solder a 8" hook-up wire to a small copper plate and bolt the plate to the screw from inside as below.

        Solder a 4" hook-up wire to another half of the lock.

 

Schematic Diagram

 

Wiring diagram

 

Assembling

Solder the parts according to the wiring diagram. Arrange the LEDs so that they are evenly spread over the box. Then put a cassette case on top of them. The case functions as a tray.

Fill the tray with diamonds. Test the circuit by shorting the lock with a wire. The LEDs should turn OFF.

 

The Treasure Box Rev 2

The circuit draws 0.4mA when the lid is closed, 0.2A when the lid is open. The battery can last for around 2 months even the lid is closed. Then the batteries need replacement. It does sound that great. So I reworked it using MOSFET instead of bipolar transistor. The battery pack was replaced with 3.6V 700mAh Nicad battery pack which are commonly used in cordless phone. The new circuit diagram is as following:

The MOSFET needs to be turned ON with a gate voltage of 3V or less. The gate threshold voltage of IRLD024 is only 2V(max) so it is a good choice. The circuit draws only 1.2 uA when the lid is closed, almost nothing. The number of LEDs is increased to 8 to enhance the illumination.

 

 

End of the project

 

 

Home made Seismograph for classroom demonstration

This project only covers the sensor - the equipment to record or to show the signal can be a strip chart recorder, an X-Y recorder or an oscilloscope, which will not be discussed here.

Material: A 12" (or bigger) subwoofer speaker.

Tool: a utility knife

Procedure: Remove the foam surround of the speaker with a utility knife, that's it.

 

Theory of Operation:

 

The seismograph is a paper cone suspended by a diaphragm. The gravitational attraction of the paper cone is canceled by the tension of the diaphragm, thus holding the paper cone in position. When the ground moves, the magnet also moves and the paper cone, because it catches air and has inertia, tries to remain still. The coil, which is mounted at the bottom of the paper cone, will  change position relative to the magnet, which cause current flowing in the coil. The current can be observed with an oscilloscope. 

 

End of the project

LED Flash Light Mod

Flashlights using white LEDs are now widely available. The price has been rolling down rapidly since their first introduction to the market. Some pretty good looking models ( with machined aluminum body) are selling at $4 each. I saw a 3-pack 1W LED flash light that is selling at $17 at Costco. They are cheap models and their performance are not comparable with those high end models which use Luxeon III LEDs with well designed optics. Most cheap models use 3 x AAA batteries and won't last long (9 LEDs take 0.3A in total). I modified one so that it uses 3 x C type NiCd batteries. The modified one is no longer pocket size but still handy.

Material list

Item Description Qty
1 C-type NiCd battery (with solder tab) 3
2 Aluminum body (cut from a handle of a paint roller). Select the size which the battery can be fitted in.   1
3 A LED flash light. Select those with a removable head assembly and that its size fits the body.  1
4 Miniature toggle switch 1
5 DC power jack 1
6 AWG 26 hook-up wires  2 ft.

Drawing

      

Construction Steps

1.     Solder the hook-up wires to the toggle switch, the DC jack and the batteries.

2.    Install the DC jack on the body. Stuff some paper between the jack and the battery for segregation.

3.    Install the switch at the bottom of the handle and then insert the batteries into the body. Stuff some paper between the switch and the battery for segregation.

2.    Solder the hook-up wires to the LED head assembly.

4.    Completed.

 

For performance reviews on commercial models, go to http://www.flashlightreviews.com/index1.html

 

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End of the project

 

 

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