1How to make your own piezo speaker / buzzer
Get your parts. You need a raw "piezo with feedback" disk element that is rated for 2.8 KHz frequency. (These instructions will work for 2.7 KHz - 3.5 KHz.) The important thing is be sure that your piezo has feedback (MFG). Digikey sells them, and I've also bought some on eBay.
You will also need the following electronic components (all through-hole):
-- One each of 330 ohm, 1.5K, and 220K carbon film resistors
-- One BC547 transistor
-- 22 gauge (or less) wire in three colors (corresponding to MFG of the piezo).
-- Soldering equipment
Manufacture your circuit board. You can either work from my schematic ("Piezo_amplifier2") or send my Gerber files to a manufacturer. The files you need are uploaded to this project. If you're unsure about my circuit, then breadboard it first.
Solder your board. Be careful soldering to the piezo disk - they are delicate. Avoid stiff wire for this part. Give yourself enough length that you can position the piezo but not so much that you have extra bulk. Unless you are adding an optional resistor to my amplifier board (see R4) --and you probably aren't-- then put a jumper to ground here. Give yourself longer wires on "input" and "GND" so you have something to work with. These are where you will connect to the audio signal and common ground of whatever circuit is generating your sound.
Make a speaker housing. I show a example housing on my blog that I vacuum formed out of 0.08" acrylic and laser cut to a round shape with a backing. You can also make something quick and dirty out of cardboard or scrap plastic. The amplified piezo will make sound without the housing (but it won't be as loud and the sound will be thinner.)
Put your piezo and circuit board in a housing. Careful when you bend the piezo wires and don't let the components cause a short circuit. You might want to stick a thin piece of non-conductive material between the board and the piezo disk, but remember that anything touching the piezo will likely change its sound quality. You can play with this, too, by stuffing non-conductive materials into the housing - like cotton or foam. I've tried affixing the piezo disk to the housing with a short piece of plastic tubing superglued to the center. That works well. Play around with it until you get the sound quality that you like.
Connect your speaker to a low voltage audio signal and common ground. By low voltage I mean like 6-12 volts. It might work with higher voltage but I haven't tested it. I will add of couple of animal circuits to this project that you can build to generate the audio signal.
2How to make a chirping cricket from discrete transistors
Get my schematic. Download my project file "Heaton_transistor cricket.jpg."
Get the following equipment (skip this step if you're an experienced hacker):
-- 12 volt DC power supply (a 9 volt battery will work if that's what you've got)
-- Breadboard (then solder freeform, or in perfboard, or make a printed circuit board...or build your circuit into paper or fabric or whatever if you're crazy like me)
-- 22 gauge solid hook-up wire, wire strippers, flush wire cutters (and solder + iron if you decide to make your cricket permanent)
-- Some way to connect power to your breadboard. I use a 12 volt DC "wall wart" power supply with a 5.5 x 2.1 mm male plug, and I connect it to my breadboard using a mating female barrel power jack that has 22 gauge wire leads soldered on... remember, most power supplies are "center positive" but always good to check...)
-- Optional: a multimeter and oscilloscope, especially the oscilloscope will enable you to look at the chirp waveform
Get the following parts:
5 :: 2N3904 transistors
1 :: 2N3906 transistor
3 :: 1K carbon film resistors
1 :: 4.7K carbon film resistor
3 :: 10K carbon film resistors
4 :: 12K carbon film resistors
1 :: 220K carbon film resistor
1 :: 0.1 uF ceramic capacitor
2 :: 2.2 uF electrolytic capacitor
1 :: 4.7 uF electrolytic capacitor
1 :: 47 uF electrolytic capacitor
1 :: 100 uF electrolytic capacitor
1 :: Piezo electric speaker (buzzer) that is responsive in the 2.8 KHz range
2 :: LEDs
+1 :: 10K carbon film resistor
1 :: 30K carbon film resistor
Other resistor and electrolytic capacitor values to play with, maybe some variable resistors (potentiometers) if you want a cricket that is easy to adjust
Other piezo electric speakers to play with (i.e., piezo elements that are sensitive at other frequencies, or speakers with a different physical housing). You can try 8 ohm speakers (and should for insight) but I doubt you'll like the sound if "cricket" is your aim.
Extra components (especially transistors) if you intend to tweak the circuit because you might fry something.
Build a cricket according to my schematic.
3How to draw if you have no artistic talent
Use a tracing projector!
A lot of people will argue that this method is cheating --to which I say, cheating who? Andy Warhol regularly traced his images, as have many other artists throughout history.
There's more than one way to do this, but here's a set-up that I like:
-- On your computer, get a digital image that you want to trace and open it in a photo viewer of any kind. Photo editing software is handy if you want to zoom in, scale, enhance contrast (for improved visibility), or otherwise change the image.
-- Adjust your computer's system settings so that it won't go to sleep or launch the screen saver.
-- Hook up a projector to your computer, for example, this reasonably priced mini projector available on Amazon
-- Hang a sheet of paper on the wall and project your image onto it. Move the projector closer or farther away to get the size that you want.
-- Trace it.
4How to build a more complicated insect (like a Katydid or Tree Cricket)
-- Set up your prototyping bench. You need a nice sized breadboard plus a variety of electronic components, multimeter, wire strippers, 12V DC power supply, solid stranded wire, and ideally an oscilloscope. It's hard to figure out what is wrong if you can't probe the signal.
-- Print out one or more of my schematics (see project files). Choose only one to build, but comparing different designs might help you to understand how the circuit elements are working.
-- Start by building the basic circuit. I have annotated my schematics where components are optional. Note that I put values in (parentheses) when the value is variable, and I use an *asterix when the component is optional.
-- Build the circuit in functional sections and test along the way. It's much better to get a part of the circuit working than to build the whole thing and have it not work (because then you have more circuit to debug).
-- When in doubt, always use a multimeter to test that power and ground are NOT connected (before you plug in your power supply).
-- Be careful and systematic. Use color-coded wires (black for ground, red for power, white for signal, etc.) You can get more expressive later when you have a functional circuit.
-- Keep a notebook with your observations and any changes to the design.
-- Don't get impatient or frustrated. Electricity is a very unforgiving medium, but with experience you will learn to find and correct mistakes quickly. If there's a component or design element that you don't understand, search the web / watch YouTube videos, etc. That's how I learned the basics (and everything else came from trial and error).
-- Get one or more copies of "how to" books by Forrest Mims III. His circuits and explanations are very clear and easy to reproduce.
5How to build a Mother Nature Board
-- You need a large breadboard plus a variety of electronic components, multimeter, wire strippers, 12V DC power supply, solid stranded wire, and ideally an oscilloscope. It's hard to figure out what is wrong if you can't probe the signal.
-- Download my files KHeaton_HNM_block diagram.pdf and Mother Nature Board (random pulse gen).pdf. I also recommend that you read Aaron Logue and Charles Platt's article on how to make a really random number generator.
-- Build the circuit in functional sections and test along the way. It's much better to get a part of the circuit working than to build the whole thing and have it not work (because then you have more circuit to debug). Definitely use LEDs wherever possible so you can see what's happening.
-- If you have trouble getting noise out of your transistor, try a different one. I found that some transistors worked while others didn't (all 2N3904... go figure). You might also try increasing the noise amplification.
-- Once you get your random number generator working, you might be wise to build a little bank of amplifier circuits (i.e. common emitter) to buffer the pulses out of the logic ICs. Many logic ICs can't sink a lot of current. If you're lucky, you can skip this step but consider yourself warned. Current gets scarce especially when you add LEDs to see what's happening.
-- Build some discrete transistor logic gates or get some logic ICs. At least for prototyping, I like the discrete transistor gates because you can add as many inputs as you want (to make an event trigger more or less frequently).
-- Play around with inputs to your logic gates until you get patterns with timing that you like.
-- Buffer the signal out of your logic gate using the same method as before (common emitter amplifier should work).
-- Connect the buffered output to pin 2 of a 555 timer in monostable (aka "one-shot") configuration. Remember that pin 2 is triggered by a low pulse (so invert your trigger as necessary). Select the R and C values on DIS and THR (pins 6 & 7) of the 555 to set the duration of pulse out on pin 3 (in other words, when the one-shot is triggered, 3 will go high for a duration of time set by the RC values). If the duration is longer than your trigger frequency, then the one-shot will basically never turn off. Design accordingly.
-- Connect the output of the one-shot (pin 3) to a mosfet configured as a switch. I provide a sketch for a simple mosfet switch design in Mother Nature in perfboard (+ more tips). One way to use this type of switch is to connect the ground of your sound generator to the mosfet's drain and the sound generator's power lead to 12V DC (or whatever voltage it wants). You can also use the mosfet to pull an aspect of a sound generator circuit to ground, such as the emitter of an NPN transistor.
-- Happy natural chorus!