• Chickpeas Can Bell

    02/15/2021 at 05:23 0 comments

    This article is about a bell made from Chickpeas can.

    You can see the bell working in this video:

    Step 1: Attach the Washer to Bell

    Make a hole and insert the bell sound making washer.

    You can see the bell in another photo:


    You can try other material types (zinc, copper, iron, tin, solder, aluminium, brass, steel, nickel), other shapes or other amounts of sound making objects to change the bell sound.

  • Computer Fan Aircon

    01/20/2021 at 08:22 0 comments

    This article is about the air conditioner that can be made from a computer fan.

    The fan blows the air out of the plastic box filled with ice to cool the ambient temperature.

    Aircon 1:

    Aircon 2:

    I thought of this idea when my brother found a few old computer fans on the street soaking in the rain.

    Step 1: Design the Fan

    This idea is not new and there are a number of videos on YouTube.

    My design does not include the lid. You might need this if you are putting your fan in your car because the car could me moving on a rocky or bumpy road turning inside contents upside down. You can try using food containers with the lid to avoid this problem.

    Step 2: Make the Fan

    The first thought that comes to mind is which way I attach the fan to the plastic container. One side is sucking air in and the other side is blowing the air out.

    We all know that if we put a hand near the computer fan at the back of a typical desktop PC we will feel a blow of air, flowing out of the computer. This is why there is no need to connect the fan to the 12 V battery before attaching this component to the plastic package. We know what the back of the computer fans looks like:

    Aircon 1:

    Aircon 2:

    Step 3: Testing

    I connected the two aircons that I made to 12 V battery:

    Aircon 2:

    Step 4: Testing With the Ice

    Aircon 1:

    Aircon 2:

    Step 5: Testing Tricks

    Aircon 1:

    Aircon 2:

  • Transistor Comparator

    04/06/2020 at 13:34 0 comments

    This page shows you how to make a transistor comparator.

    Step 1: Design the Circuit

    Resistors R1 and R2 are connected in voltage divider configuration and chosen so small in value that the maximum transistor Q2 emitter current is not affecting the emitter voltage, Ve.

    Resistor Ro is used for short circuit protection. 

    Circuit 1:

    Calculate maximum input current:

    IinMax = IbMax = (Ve - Vbe * 2) / Rb

    = (Vs / 2  - Vbe * 2) / Rb

    = (1.5 V - 0.7 V *2) / 100,000 ohms = 0.1 V / 100,000 ohms

    = 1 / 1,000,000 = 1 uA

    Circuit 2:

    The second circuit is an improvement of the first ciricuit because is allows a reduction in collector emitter voltage, Vce and thus lower Q1 transistor power dissipation.

    Calculate maximum input current:

    IinMax = IbMax = (Ve - Vbe * 2) / Rb / BetaMin

    (Where: Beta = Transistor Current Gain = Collector Current / Base Current)

    = (Vs / 2  - Vbe * 2) / Rb / BetaMin

    = (1.5 V - 0.7 V *2) / 10,000 ohms / 20 = 0.1 V / 200,000 ohms

    = 1 / 2,000,000 = 0.5 uA = 500 nA

    Calculate maximum emitter current, Ie:

    IeMax = IbMax * BetaMin * BetaMin

    = 500 nA * 20 * 20 = 500 nA * 4 * 100

    = 2 uA * 100 = 200 uA

    A typical transistor current gain is 100 and some transistors have current gains as high as 500. Thus IeMax could be:

    IeMax = IbMax * BetaMin * BetaMin

    = 500 nA * 100 * 100 = 500 nA * 10,000

    = 0.5 uA * 10,000 = 5 uA * 1,000 = 5 mA

    Step 2: Simulations

    The wave forms are:

    Blue: Vi, Input

    Green: Ve, Comparing Voltage

    Red: Vl, Output

    Circuit 1:

    Circuit 2:

    Simulations show no significant difference in the output of the two circuits.

    Step 3: Make the Circuit

    I made Circuit 1 by twisting wires together with pliers. I did not use a soldering iron. You an see the photo of my circuit above.

    Step 4: Test the Circuit

    I used 9 V input voltage instead 3 V because my voltmeter resistance was only 3,000 ohms, thus creating a loading an output effect and thus reducing the maximum output voltage.

    If you find during testing that the input is affecting the transistor Q2 emitter voltage, Ve then try reducing R1 and R2 values and/or increasing Rb value. Do not reduce R1 and R2 values below about 330 ohms. Otherwise you will draw high currents from your battery/power supply and might cause power supply failure.