Audio Easter Egg

Build Your Own Audio Easter Egg

Difficulty: Beginner
Assembly Time: 2 hours
Designer: Dave1 aka David Allen Thom

The Audio Easter Egg is great for treasure hunts, games or just a fun novelty. It emits a chick sounding chirp at delayed intervals and is built into any plastic egg that is 2" or larger diameter. The circuit fills the shorter half of the egg, and most of the rest of space is available for candy or prizes. Originally designed for the blind, this little gadget is fun for all, especially when you build several and create a chirping egg basket. The circuit is based on multiple oscillators built from a single 74HC05 Hex inverter.

Build your own Audio Easter Eggs

Step-by-Step Instructions

Step 1 – Board Prep

Make sure the board is clean; study it to be sure you understand the component locations. The photo, (above right), shows the topside component locations in yellow and the copper side is visible as an x-ray view in red. Insert parts from component side and solder on the "red" or copper side.

If your board is square, and if you want to install it into a plastic egg less than 3" diameter, you will need to cut it into an octagon before starting. Measure along the edge of the board 3/8" from each corner and make a mark, (eight marks total two per edge). Cut the board into an octagon (as seen by blue outline in photo above right) by trimming off the corners.

Be careful when cutting to make sure you do not get too close to the copper! It is better to trim less and use a file while test fitting the board into the egg or container you want to install it in. You can also cut the board with a hacksaw, or scroll saw, but be very careful with power tools as it is difficult to hold a small object while cutting. If you don't want to try that you can file or sand the corners with coarse sandpaper until it will fit as you like.

Think of it as exercise. Do not proceed until your bare board fits as you want it to. Wear a protective mask when cutting or sanding the PCB.

Step 2 – Solder IC Hex Inverter

Locate the U1 pin 1 designator on the PC board. Locate pin 1 on the IC chip. Bend each row of the chip's pins slightly by laying it on a solid surface and bending leads inward toward centerline of chip. Check the fit in PC board holes, repeat until fit is correct. Install so that pin 1 on chip is in pin 1 hole of PC card.

Solder one pin only, check to make sure the chip is still properly seated in the PC card solder the opposite pin, again check fit. If it is OK then solder the rest of the pins. Avoid excess heat to pins and board. When complete, trim excess lead length with diagonal cutters.

IC chip pin locationsIC chip pin locations

Step 3 – Solder Resistors

Locate R1 (470K Resistor Yellow / Violet / Yellow). Bend the leads (shown right) for vertical mount; all the resistors will be installed this way. Install in designated location below pins 1 (designated on copper side of board) and pin 2 of U1 (74HC04 chip). Solder and trim leads.

Install R2 (680K Resistor Blue / Grey / Yellow) in designated location near R1, solder and trim leads.

Install R3 (100K Resistor Brown / Black / Yellow) in designated location near pin 8, end of U1, solder and trim leads.

Install R4 (220K Resistor Red / Red / Yellow) above U1 pins 9 and10, solder and trim leads.

Install R5 (10K Resistor Brown / Black / Orange) above pin 11 of U1 (to left of R4), solder and trim leads.

Bend the resistor leads for vertical mountingBend the resistor leads for vertical mounting

Step 4 – Solder Capacitors

Locate C1 (10µF Electrolytic Capacitor). It will be a small tubular cylinder shape. Note one side will have a printed stripe down the vertical length. This designates the negative pin for the capacitor. The PC board will be marked with a "+" sign on the positive pin side. Be sure to install the negative pin in the hole opposite the one with the "+" sign; your board will not work if polarity is incorrect. Solder and trim excess leads.

C1: 10µF Electrolytic CapacitorC1: 10µF Electrolytic Capacitor

C2: 0.1µF Monolithic CapacitorC2: 0.1µF Monolithic Capacitor

C4: 0.0022µF Ceramic Disc CapacitorC4: 0.0022µF Ceramic Disc Capacitor

Install C2 (0.1µF monolithic capacitor) beside C1 near pin 1 and end of U1. Solder leads and trim excess.

Locate C3 (2.2µF aluminum electrolytic capacitor), it looks similar to C1. Note negative side of cap and locate negative hole in C3, location almost directly below R2. Solder and trim excess leads.

Install C4 (0.0022µF ceramic disc capacitor) at the top right of board above R4. Solder and trim excess lead length.

Step 5 – Solder the Diodes

Locate D1 - 1N4148 Diode and install near the top left of the board. This diode may look a lot like D2! Try to locate the 1N4148 number on the diode, or the last part of the number. Be sure you can tell D1 and D2 apart before proceeding.

Note the black band around one end. This is indicated on the circuit board by a >| symbol where the bar indicates the end of the black band. Be sure the band is installed in the hole nearest the bar. This will be a vertical mount like the resistors. Solder and trim excess lead length.

Locate D2 the Zener Diode. It will be marked with 1N5225B or in some cases, the last part of that number. It may look a lot like D1! Note the banded end. The PC board will be marked with a >] at that location where the ] bracket indicates the banded end. Install, solder and cut off excess lead length.


Step 6 – 9V Battery Snap

Locate the 9V battery snap - red lead indicates V+ and the black lead is ground or GND. The PC board is marked for these. If you are comfortable with cutting and stripping the wires it is a good idea to shorten both leads to about 2 1/2" each. Otherwise, just install them as they come; it just makes a bit more wire inside the egg. Be sure to solder the red lead to the V+ hole near the left side of the board.

The black lead goes to the GND hole at the far right of the board, to the right of R3. It is a good idea to use a small dab of hot glue to secure the wires on the top surface of the board where they come out to prevent them from breaking easily.

Battery snapBattery snap

Step 7 – Piezo Speaker

Locate Piezo Speaker. Note the red and black leads. The PC board is marked with SPK+ for the red lead and SPK - for the black lead. Solder in place and use a dab of hot glue to hold the wires.

Piezo speakerPiezo speaker

Step 8 – Testing

At this point it is a good idea to check all the component placements, check the solder connections, and to look for spots where you might have solder bridged two pins by mistake. The only pin sets on U1 that should be bridged are pins 4 and 5 and pins 9 and 10. If there are bridges between any others, try to remove them. Check the two aluminum electrolytic caps to be sure the polarity (+ and - pins) is correct. Double-check the diode placements against the board designators. You can clean the solder side of the board with rubbing alcohol and a small brush to make it easier to find problems and have a better looking product. If everything looks good, snap on a 9V battery and within about 10 seconds the chirping should begin!

Step 9 – Assemble the Egg

First drill a small hole about 1/16th to 1/8th" in the end of the short half of the egg, (smaller is better). Push the speaker as far as it will go into the bottom with the hole in the speaker centered over the hole in the egg. Use hot glue to secure it. When cool, place PC board over the top of the speaker pushed down as far as it will go with speaker wire coiled under PC board. Secure with a couple of dabs of hot glue.

The next step is optional - spray small amount of expanding foam over top of PC board, cover with a layer of plastic wrap and then firmly push long edge of the battery into the center. Tape battery into position, when the expanding foam hardens, you will be able to cut and peel away any excess that gets over the side of the egg. This forms a nice niche for the battery to fit in, but is not necessary. Alternately, you can cut a circle of 1/4" foam rubber and place that between the PC card and battery to insulate, even cardboard will work, you are just trying to keep the battery from shorting out on the PC card components. When done, test again, insert candy or other treasures and hide it!

Plastic EggPlastic Egg

Step 10 – Audio Easter Egg Extras

Changing Personalities
If you want to create more eggs, you may want some to have a different personality. You can do this by changing values of R1, R2, or R4, or changing all of them. In general you can usually go from about 1/2 the given values up to twice the given values. Although some combinations may not be desirable!

R1 - Larger makes the delay before chirping longer - smaller makes it shorter.

R4 - Larger lowers the chirping pitch, smaller makes it higher.

R2 - Changes "chirp ramp up", smaller makes short ramp, larger equals longer ramp.

Making multiple eggs with the same or different voices creates a fun cacophony of chirping craziness which most people will find irresistibly funny!

Talk to your local charities about building a bunch of these for blind children - they will love it.


About the designer

David Allen Thom Dave recalls first being inspired by Sputnik, although he didn't know how, or for that matter, even what a satellite did. Fortunately, that didn't stop him from trying. He first built and electronic metronome at 12, from a magazine and these projects fueled his passion for electronics. He built an electric tic-tac-toe from a Popular Science article and a Psych-Tone from Popular Electronics in the 1970s. Dave said, "I still remember my first Jameco catalog, just a few pages as I recall. Some of my recent projects sport some parts from my early purchases!"

Dave studied Electronics Engineering Technology and after some years in the field, he was recruited to teach at a college linked technical high school, where he co-developed a four year Electronics Engineering program and remained there for 30 years until retirement. He now participates as a volunteer firefighter in his rural neighborhood of south central Washington and still designs electronics, just at a slower pace.

Follow Dave on youtube at MrDAT9000