# A Magnet-Motivated Bird

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## Introduction: A Magnet-Motivated Bird

The project shows you how to make a toy that represents a bird who tweets as you motivate it to do so. The bird has a specific organ of senses called ‘reed switch’; as a magnet approaches to this element the contacts close and the electronic circuit is energized - then sounds come out. I used a small magnetic stick from a kids toy, slightly disguised as a microphone with its upper part made of styrofoam, to ‘motivate’ the bird; you are free to choose any other form of motivation provided that a magnet is included into it.

### Supplies:

Components needed for the circuit

Integrated circuit NE555 - 1 pcs

Transistors 2N3904 - 4 pcs

Potentiometers or trimmers 100K - 2 pcs

Resistors:

10K - 2 pcs

2.2K - 2 pcs

1K - 3 pcs

100 Ohm - 1 pcs

Electrolytic capacitors (voltage at least 10 V):

Ceramic capacitors (voltage 50 V):

Small loudspeaker with 8 Ohm coil

Socket for the integrated circuit

Connector for a 9V battery

9V battery

A piece of perforated textolite plate

Wires

Tools needed to build the circuit

Soldering gun with solder

Wire cutters

Tweezers

Exacto knife

Materials and tools needed to build the bird's figure

It depends on how you would make the bird. I don’t exclude that somebody would be able to 3D print both the bird and the enclosure for its electronic part. I made the bird of FIMO paste and used an empty tea box to make the enclosure. The proceeding is described in Bird’s Body and Enclosure sections.

### Teacher Notes

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## Step 1: Electronic Circuit

The circuit consists of two astable multivibrators. The first one is built with an IC NE 555 and produces pulses with a very low frequency that determines the interval between the ‘tweet packets’. The frequency can be changed by means of the potentiometer R2.

Let’s transform the general formula (see Reference section) for the pulse frequency of this kind of multivibrator taking into account the potentiometer R2; for example, when its slider is in the centre position the pulse frequency is:

f = 1.44 / (60 KOhm + 2*60 KOhm) * 50 microfarad = 0.16 1/s, which means that a pulse appears at the IC output every 6.25 sec

This pulse arrives to the base of Q1 and opens it; thus, the second multivibrator get energized.

This multivibrator is built with the transistors Q2 and Q3; without the C3 and R7 it would be an ordinary astable multivibrator (see reference) the pulse frequency of which is calculated with the formula:

f = 1.38 / R*C

Thus, f = 1.38 / 2.2 KOhm * 0.1 microfarad = 3294 1/s

This frequency determines the pitch of a tweet. The potentiometer R7 and capacitor C3 determine the interval between the tweets.

Let’s suppose that C3 is fully discharged before the circuit gets energized; the capacitor begins charging through R6, R8 and the base-emitter junctions of Q2 and Q3; the current flows through C3, and the circuit works. When C3 is fully charged, its upper plate is positive, and lower plate is negative; therefore, Q2 and Q3 close.

C3 begins discharging through the potentiometer R7; thus, the time of discharge can be varied. Once C3 is discharged it begins recharging, the current flows again, the circuit works and produces a ‘tweet’.

C3 is composed of two capacitors: one of 4.7 and the other of 100 microfarad; I tried different values of C3 to make the tone sound more or less like a real bird tweet; you are also free to play with the value of R7 to modify the tones.

The pulse from the collector of Q3 arrives, through R10, to the base of Q4; the latter opens, and the pulse is being heard in the loudspeaker. A female connector for the reed contact is installed in the '+' line; this feature, combined with the male connector of the reed contact (magnetic switch, MSW) allows to disconnect the bird's figure from the circuit, if required.

The circuit is assembled on a 35 x 70 mm piece of perforated textolite.

## Step 2: Reed Contact

The contact consists of:

a 50 x 2 mm stripe of copper-clad textolite - this is the base of the contact

a 50 x 1 mm stripe of 0.5 mm thin iron sheet - this is the reed that plies under the action of magnetic field

a 2 X 5 mm piece of plastic - to fix the reed on its base and provide their mutual isolation; this piece is glued with epoxy resin

a 2 x 5 mm piece of 1 mm thick iron plate - soldered at the reed’s end to increase the force of magnetic attraction; in fact, most of this force is applied to this weight which, in turn, makes the reed ply

The sensitivity of the reed depends on its length, width and thickness; a thinner reed would increase the sensing range even if the other parameters (length, width, mass of end piece, magnetic force) remain unchanged.

The contact is marked as MSW (magnetic switch) on the circuit drawing. When a magnet is approached to the contact, the latter closes and the circuit gets energized.

## Step 3: Bird's Figure

This bird is inspired not only by a well-known bird, but also by the Black-naped Monarch (Hypothymis Azurea).

The figure is made of blue FIMO paste. I fabricated patterns for the wings to make them of the same regular shape and cut the of 1.5 mm thin sheet of FIMO paste. Each leg has a frame made of 1 mm thick tinned copper wire; this frame not only reinforces the legs but also serves to fix the figure on the enclosure’s cover. Pictures show how to make such kind of frame.

I also made a pattern for the body but used it rather as a reference while making the body 'free hand'.

After all elements of the figure are assembled, and the figure looks according to your artistic concepts, it should be cured at 130 degrees C (not more !!!) during 30 minutes; this operation could be performed in a home baking oven.

After the figure is cured, a channel should be made to pass the wires of the reed contact; I made this channel as a combination of two drilled 4 mm-diameter holes.

To pass the wires through the channel, I passed a piece of thick fishing line, attached an end of the wires to the line and pulled them through. After that, I installed the reed contact in the channel and glued the beak made of thick paper.

## Step 4: Enclosure

I used an empty tea can to make the enclosure for the circuit. The cover has two 1 mm holes for the bird’s legs, and a 3 mm holes for the reed contact’s wires. A male connector is installed on the free ends of the wires which allows to detach the bird with the cover from the enclosure, if required. The legs’ frames are installed in the 1 mm holes and soldered to the cover; thus, the figure is held in position.

A battery holder made of 0.5 mm thick metal plate is soldered to the enclosure’s bottom.

A segment-shaped piece of cardboard is glued to the enclosure’s bottom to isolate the circuit from the enclosure.

The loudspeaker is installed on a piece of cardboard fixed both to the bottom and the walls of the enclosure by means of molten glue-gun plastic.

Sixteen 2 mm holes are drilled in the enclosure’s side according to a pattern, to open way to the sound; you are free to produce your own pattern, but it’s desirable to make the holes’ total area more or less equal to the sound-emitting area of the loudspeaker.

## Step 5: References

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