Astable Multivibrator Using Transistors (MSB056E)

Two transistor are used in this configuration, They control two LEDs that blink alternately. Speed of the effect is given by C1 and C2. In the simulation we used 1 µF instead 4,7 µF to speed up the simulation. You can change the values to see how they affect the speed.










Obs.: we used transistors 2N222 instead the BC548.



To download the simulation files and Netlist - click here (

Plasma Oscillator (MIN050E)

A flame is a conductive medium that can be used in an uncommon feedback loop to control the frequency of an audio oscillator.

This configuration can be used as a confirmation of the conductivity of a flame.

The audio oscillator described in this project is controlled by the “fourth” matter state, the “plasma” or an ionized gas, and can be used as part of an interesting experiment in physics.

The flame can be produced by a simple match or a candle and the flickering effect will modulate the generated sound.

The circuit runs in frequencies between 1 and 500 Hz, depending on the electrodes and flame positions.

A schematic diagram of the Plasma Oscillator is shown in Figure 1.


Figure 1 – Schematic diagram of the Plasma Oscillator
Figure 1 – Schematic diagram of the Plasma Oscillator


The high input impedance of a 4093 is fundamental in this project. A flame typically has a resistance in the range of tenths of megohm.

The printed circuit board for the components positioning is shown in figure 2.


Figure 2 – PCB for the project
Figure 2 – PCB for the project


Sensor details are also given in that figure. Two wires, one placed near the other, with about 1 inch of bared length as shown in the figure, form the “plasma sensor".

The flame should involve the two bared wires at the same time to allow the feedback current to flow and the oscillator to operate.

An output stage using a piezoelectric transducer can replace the transistor and loudspeaker. With a lower current drain this configuration can be powered from four AA cells or a 9V battery.


Plasma Oscillator

IC1 - 4093B CMOS Integrated Circuit

SPKR - 4/8 ohm 4-inch loudspeaker

Q1 - BD135 or TIP31 Power NPN silicon transistor

R1 - 10,000 ohm, ¼ W, 5% resistor

R2 - 1,000 ohm, ¼ W, 5% resistor

X1 - Plasma sensor - see text

C1 - 1,000 to 4,700 pF ceramic or metal film capacitor


Ideas to Explore

To get better performance or to learn more about the circuit:

Explain why the circuit doesn’t operate using a neon or fluorescent lamp as a plasma medium.

Explain what “plasma” is.

You can alter this circuit to use it as a flame alarm.


Science applications:

- Off course, the basic idea of this project is to use it in an experiment involving plasma. Plasma is produced when an ionized gas loses electrons. The the gas converts in a “soup” of free electrons and ionized atoms.

- Use different kinds of flames, such as those produced by matches, gas, paper, etc., and compare their conductivity by the tone pitch.


High-Power Audio Oscillator (E) (MIN018E)

This high-power version of an audio oscillator produces a strong audible tone using a piezoelectric transducer.

All four gates existing in the 4093 IC are used in this project to drive the transducer with a good audio signal.

The circuit can be used in alarms, toys, as a standalone project to teach about oscillators specifically, or in experiments using continuous sounds in the frequency range between 100 and 10,000 Hz.

The recommended piezoelectric transducer emits maximum output power between 700 and 3,000 Hz, but it will also operate in other frequencies with Iess power.

Power supply voltage range is between 5 and 12 volts.

Current requirements depend upon the power supply voltage, ranging from 10 to 50 mA typically.

P1 adjusts the tone frequency. C1 can be altered within a Iarge range of values as indicated in the schematic diagram, shown in Flgure 1.


Figure 1 – Schematics for the oscillator
Figure 1 – Schematics for the oscillator



Components placement on a printed-circuit board is shown in Flgure 2.



Figure 2 – Mounting on a printed circuit board
Figure 2 – Mounting on a printed circuit board



You can also mount the circuit using a solderless board for experimental applications.

AII the components and the batteries (if used as power supply) can be housed in a small plastic box. BZ can be replaced with a common piezoelectric tweeter.

But, in this case, you should open the tweeter and remove the small transformer from inside it.

Then the output of the circuit should be oonnected directly to the small piezo-electric transducer.


Power Audio Osclllator

IC1 - 40933 CMOS integrated circuit

BZ - Piezoelectric transducer

(Radio Shack 273-090 or equivalent)

P1 - 100,000 ohm potentiometer

R1 - 10,000 ohm, 1/4W, 5% resistor

C1 - 1200 pF to 0.047 µF ceramic or metal film capacitor


Ideas to Explore

To Iearn more about oomponents and devices

This circuit can also produce sound in the ultrasound band. Using a 1,200 pF capacitor for C1, the range will reach an upper Iimit of about 100,000 Hz.

Explain how a push-pull output stage operates.


Science and uncommon applications:

This circuit can be used for animal conditioning or in experiments involving sounds.

O By replacing P1 with sensors, such as LDRs (Light Dependent Resistors) or NTCs (Negative-Temperature Coefficient resistors), tone frequency will be Iight-dependent or temperature-dependent.

By replacing P1 with touch sensors or electrodes, we can use the circuit as Iier detector or bio-feedback devices. The sound pitch will depend upon skin resistance.

The circuit can also be used as a fish attractor or in experiments involving water animals and sounds. Replacing BZ with wires immersed into water will generate electric current fields for experimental worksinvolving the influence of these fields on fish or other beings.

Some animals, such as mice and rats, are scared off by ultrasounds.The circuit can be used in experiments to determine the frequencies that are more effective for this task.


See other projects involving sounds in this site for new ideas to explore.


Note: This circuit is part of the author’s book Fun Projects for the Experimenter Vol1 – TAB Books – 1998 (link para download)



Sequence Generator (MIN043)

An astable multivibrator, put to work by using it as a source of clock pulses for a 4017 counter, is the basis for this circuit.

We can use it to generate random numbers in a range of one-of-ten or as a 0-to-9 counter in science projects or in other applications.

You can also adjust the clock so that it supplies one pulse each second for using the circuit as a timer in scientific experiments or at home.

If you alter the clock pulse frequency, time range can be changed so that it supplies one pulse each minute or ten minutes. In this case, the time range will rise to 9 minutes or 90 minutes (in 1- or 10-minute steps).

As a sequence generator in logic circuits demonstrations, you can change the astable operation of the 555 to monostable, connecting a momentary switch or any sensor that can be used to trigger it.

The circuit can be powered from 6 to 12 V supplies, and R3 depends upon the voltage of the power supply.

Use a 470 ohm resistor if the supply voltage is 6 V. Use a 1,000 ohm resistor if the power supply used is 12 V.

Capacitor C1 determines the pulse rate range and can be altered. Values between 1 and 1,000 µF can be used. Remember that higher values mean lower pulse rate.

P1 adjusts the pulse rate within 100:1, depending on the capacitor used.

Figure 1 shows the schematic diagram of the sequence Generator.


Figure 1 – Schematic diagram of the Sequencer Generator
Figure 1 – Schematic diagram of the Sequencer Generator


The circuit uses a 555 IC timer to generate the clock pulses and a 4017 CMOS IC, a counter and 1-of-10 decoder to drive ten LEDs as indicators.

Components placement on a homemade printed-circuit board is shown in Figure 2.


Figure 2 – PCB for the project
Figure 2 – PCB for the project


You can also use a solderless board or breadboard to mount it.

Positions of the polarized pieces, such as the LEDs and electrolytic capacitor, should be observed.


Sequence Generator

IC1 - 555 - Integrated circuit, timer

IC2 - 4017 - CMOS Integrated circuit, counter

LEDs - Common red, yellow or green

P1 - 1,000,000 Ohm potentiometer

R1, 2 - 10,000 ohm, 1/4W, 5% resistors

R3 - 470 ohm, 1/4W, 5% resistor

C1 - 10 µF/16 WVDC electrolytic capacitor


Ideas to Explore

To learn more about the circuit or to get better performance:

Wire a momentary switch between lC1’s pin 3 and lC2’s pin 14 to control the counter. You can stop the counter any time with this switch.

Explain how counters such as the 4017 work.

Could you alter the circuit so that it counts to any value between 2 and 9?


Science and uncommon uses:

Wire the 555 as a monostable multivibrator and use an LDR as sensor to trigger it. The circuit will operate as a pulse-of-light counter.

Use this circuit in a project about computers. You can produce pulses to be counted using the experimental flip-flop described in this book.

Experiments on ESP (Extra-Sensory Perception) can be conducted using this circuit. Random numbers in a scale of 1-to-10 can be generated using this circuit.




Circuit Bench