Recycled Circuits's pages

This website is about an ultrasonic LED circuit:

The LED can be replaced with a bright LED that emits a higher light intensity.

You can see the circuit working in the video below:

I used the following transmitter connected to Dick Smith Electronics (DSE) signal generator:

Step 1: Design the Circuit

I drawn the circuit in PSpice student edition software:

Calculate maximum LED current:

IledMax  = (Vs - Vbe3 - Vce2sat - Vled) / Rd

= (9 V - 0.7 V - 0.2 V - 2 V) / 1000 ohms

= 6.1 V / 1000 ohms

= 0.0061 A = 6.1 mA

This current value is very small. You can increase the current by reducing Rd value to:

Rd = 560 ohms: IledMax = 6.1 V / 560 ohms = 10.89285714 mA

or

Rd = 470 ohms: IledMax =  6.1 V / 470 ohms = 12.9787234 mA

The current for the big LED shown in the photo should be 20 mA. However, if you are using recycled LED components, then you might end up with an LED that will burn at currents above 5 mA.

Step 2: Simulations

Time Domain:

Frequency Domain:

Step 3: Transistor Testing

This is the transistor testing circuit that I used because I only had one LED in stock:

I used to 100 ohm resistors as metal wires.

Video:

Step 4: Make the Circuit

I made the circuit without the use of the soldering iron:

You do not need to use 1 Watt resistors for this circuit that you see in the photo above. The 250 mW power rating will be sufficient for this circuit.

I used 1 Megohm value for Re1 resistor instead of 100 kohm shown in my circuit design to obtain a higher gain. The difference is not significant. I specified the 100 kohm Re1 resistor because most resistors came in a pack of five or two, thus eliminating the need for searching or buying another resistor (the 1 Megohm).

Step 5: Testing

This video shows brightness control testing:

Proximity sensor mode testing:

This article shows you how to make an audio filter from recycled components.

This is the device that I made:

You can see the circuit working in those videos:

High Pass Filtering:

Low Pass Filtering:

Inserting a Headphone Plug:

Step 1: Design the Filter

I have drawn the circuit in the old PSpice simulation software student edition version 9.1:

A typical speaker is 4, 8 or 16 ohms. Headphones have higher impedance, and resistance values.

It is not likely that the old recycled circuit will have too many bipolar capacitors. You can try using electrolytic capacitors.

I also considered connecting a switch that would connect the Rf resistor directly to the input. However, this will also short-circuit Ch1, Ch2 or Ch3. Shorting any capacitor with a button/switch will cause permanent damage to the capacitor. This is why I avoided an additional Swh switch. An alternative is to connect a 10 ohm resistor in series with the button/switch. However, this would be an extra component that you will need to look for in an old electronic recycled circuit and an additional resistor will reduce the output signal amplitude.

The impedance/reactance (measures in ohms) of the capacitor is equal to:

Xc = 1/(2*pi*f*C)

Where: f is the frequency of the sinusoidal signal. Any periodic signal can be modelled with sinusoidal of specific amplitudes and phases (time delays). This is known as the Fourier series.

The bandpass frequencies of this filter could be complicated because it depends on load (speaker) impedance/reactance/resistance. However, if we ignore the speaker impedance we can calculate the output amplitude and phase delay with the following transfer function formula (Output Voltage/Input Voltage = Vl/Vin):

Vl / Vin = 1/(j*2*pi*f*(Cl1 + Cl2 + Cl3)) / [1/(j*2*pi*f*(Ch1 + Ch2 + Ch3)) + Rf + 1/(j*2*pi*f*(Cl1 + Cl2 + Cl3)]

The amplitude magnitude will equal to:

|Vl / Vin| = 

= |1/(j*2*pi*f*(Cl1 + Cl2 + Cl3)) / [1/(j*2*pi*f*(Ch1 + Ch2 + Ch3)) + Rf + 1/(j*2*pi*f*(Cl1 + Cl2 + Cl3))]|

= 1/(2*pi*f*(Cl1 + Cl2 + Cl3)) / sqrt[Rf^2 + (1/(j*2*pi*f*(Cl1 + Cl2 + Cl3)) + 1/(j*2*pi*f*(Ch1 + Ch2 + Ch3))^2]

The amplitude magnitude will equal to:

angle[Vl / Vin] = 

= angle[1/(j*2*pi*f*(Cl1 + Cl2 + Cl3)) / [1/(j*2*pi*f*(Ch1 + Ch2 + Ch3)) + Rf + 1/(j*2*pi*f*(Cl1 + Cl2 + Cl3))]]

Step 2: Simulations

The simulations show a bandpass filter output response:

Step 3: Make the Circuit

I made the circuit by twisting the wires together. I did not use a soldering iron.

The left blue and green wires are the input, the bottom yellow wire is the high pass filtering control, the top orange wire is the low pass filtering control, and the yellow and brown wire is the output. The orange wire is the headphone output.

Conclusion

You can see from the video that some capacitors are almost blocking the audio signal while other capacitors are creating an output sound that is exactly the same as the input. A good idea would be to use 22 uF, 33 uF, and 47 uF bipolar capacitors to implement a smoother transition from loud to filtered/quiet signal.

The light bulb of this boat turns on when the boat is placed in the water. The boat has a BJT transistor water sensor that activates the light bulb.

However, a more simpler and cheaper circuit is published here:

https://www.instructables.com/id/LED-Water-Beacon/

This sensor can be also implemented with a MOSFET transistor:

https://www.instructables.com/id/MOSFET-Touch-Lamp/

You can see my boat working here:

Step 1: Design The Circuit

The circuit is designed with a simple power NPN BJT transistor fixed bias circuit and drawn with https://easyeda.com online software:

I used an old 12 V light bulb that was made for motorcycle signalling or back lights. At the rated 12 V light bulb supply voltage, the average DC current for my light bulb was 0.1 A. This current value is dependent on light bulb design and production tolerances. At smaller supply voltages the light source current will a lot less. However, modelling the equivalent resistance of the light bulb or a bright LED is beyond the scope of this article. You can use an ammeter to check how much current your light sources is consuming.

Rc1 used for short circuit protection and might not be needed. If the light bulb current is 0.1 A then the voltage across the Rc1 resistor will be:

Rc1 = Ibulb * Rc1 = 0.1 A ** 10 ohms = 1 V

Thus the 10 ohm Rc1 resistor value could be too high and not necessary. You can try using 1 ohm instead or two 2.2 ohm resistors in parallel (to reduce the power dissipation for each resistor). The power across the Rc1 resistor will equal to:

Prc1 = Irc1 * Vrc1 = Irc1*Irc1*Rc1

Rc1 = 10 ohms: Prc1 = 0.1 A * 0.1 A * 10 ohms = 0.1 W = 100 mW

Rc1 = 1 ohms: Prc1 = 0.1 A * 0.1 A * 1 ohms = 0.01 W = 10 mW

The bright LED voltage will be 2 V. Thus the Rc2 current will equal to:

Rc2 = (Vs - Vled) / Rc2 = (9 V - 2 V) / 1000 ohms = 7 mA

A typical bright LED needs 10 mA. However, I chosen 1000 ohms if the supply voltage is raised to 18 V (if you connect two 9 V batteries in series), Iled will equal to 14 mA or 12 V, if you are using a car battery (Iled will equal to 10 mA).

We also need to calculate the minimum transistor base current need turn ON the LED or light.

Maximum collector current for light bulb:

IcMax = 100 mA

Minimum base current for light bulb:

IbMin = Ic / Beta = 100 mA / 100 = 1 mA

The maximum equivalent resistance of water will equal to:

Rw = (Vs - Vbe) / IbMin = (9 V - 0.7 V) / 1 mA

= 8.3 V / 1 mA = 8300 ohms = 8.3 kohms

Maximum collector current for a typical bright LED:

IcMax = 10 mA

Minimum base current for a typical bright LED:

IbMin = Ic / Beta = 10 mA / 100 = 0.1 mA = 100 uA

The maximum equivalent resistance of water will equal to:

Rw = (Vs - Vbe) / IbMin = (9 V - 0.7 V) / 100 uA

 = 8.3 V / 100 uA = 83000 ohms = 83 kohms

Step 2: Build The Circuit

Note: The power transistor is placed face down on the photo below. You do not need a power transistor and heat sink if you are using low current bright LEDs.

Insulate the wires with electrical tape:

The red and the white cable will be placed in the water. They are connected to the bottom of the boat.

Step 3: Attach the Circuit to Boat

You can use any packaging material that floats on water or a piece of wood.

Step 4: Drill Hole for Lights

Drill a hole for the light bulb with scissors.

Step 5: Attach the Cabin

Attach boat parts with ropes and rubber band.

Step 6: Testing

I attached the 9 V battery to boat with a rubber band because my boat capsized a few times due to loose battery (the heaviest part of the boat), thus affecting the boats centre of mass.

I tried placing the boat in hot water:

I also tried increasing the Rc resistor value to 10 ohms:

Try this yourself.