Introduction: Battle of the Bands: Theremin, Organ, & APC Synthesist!

Today, we are going to be using 555 timers to create several musical instruments! We volition be building a theremin, organ, and an Atari Punk Console. I used this activity in my classroom to celebrate graduating from discrete components to integrated circuits. This activity ready-made a great segway into the residuu of the row after application the basics of resistance-capacitance (RC) circuits and semiconductors. I had ne'er seen students thus frantically solving algebraic equations to compute the perfect condenser values to tune their instruments to the true frequencies before the performances. This activity is much of entertaining and teaches many a aspects of circuit design. It also taught me the importance of adding volume knobs to circuits that make randomness. You learn that very quickly in a room filled with a dozen shriek theremins!

This project requires a bittie bit of hardware knowledge, some knowledge of RC circuits, and some breadboarding. If you aren't familiar with 555 timers, that's tight! I will teach you everything you need to know about 555 timers in the first incision.

Special thanks to Forest Mims WHO wrote or s of the best and most accessible introductory books all but electronics. His "Toy Organ" and "Stepped Tone Generator" are the basis for the Organ and Atari Punk Console. If you are interested in learning more about electronics, his Book "Getting Started in Electronics" is a great place to start. It is very well-written and comes with 100 different circuits you posterior build!

Supplies

Theremin

  • 1x 555 Timer
  • 2x Photoresistors
  • 1x 10 kOhm Resistor
  • 1x 1 MOhm Resistance
  • 1x 1 kOhm Potentiometer
  • 2x 0.1 uF Electrolytic
  • 1x 100 uF Electrolytic condenser
  • 8 Ohm Speaker (1-2 Watts) or Passive/Piezoelectric Buzzer
  • Half-size breadboard
  • Some jump shot wires
  • 9V battery
  • 9V battery clip

Organ

  • 1x 555 Timer
  • 1x 10 kOhm Resistor
  • 1x 100 kOhm Potentiometer
  • 1x 1 kOhm Potentiometer
  • 1x 0.1 uF Electrolytic Capacitor
  • 1x 100 uF Electrolytic Capacitor
  • A whole mess of diverse ceramic capacitors ranging from 1 nF to 22 uF
  • 8x (Beaver State Thomas More!) Tactile/Momentary Pushbuttons
  • 8 Ohm Loudspeaker system (1-2 Watts) or Passive/Piezoelectric Buzzer
  • Full-sized breadboard
  • Some jumper wires
  • 9V battery
  • 9V battery snip off

Atari Punk Console

  • 2x 555 Timer
  • 1x 1 kOhm Resistor
  • 2x 470 kOhm Resistor
  • 1x 1 kOhm Resistance
  • 3x 0.1 uF Electrolytic Capacitor
  • 1x 1 uF Electrolytic Capacitor
  • 1x 100 uF Electrolytic Capacitor
  • 8 Ohm Speaker (1-2 Watts) or Passive/Piezoelectric Buzzer
  • Half-size of it breadboard
  • Some jumper wires
  • 9V battery
  • 9V battery clip

Step 1: How 555 Timers Work

A 555 timekeeper is an microcircuit (IC) chip that is used to generate a square wave. It can be ill-used in timer/impudent-flop applications or as an oscillator. In this instance, we are exploitation information technology to generate square up waves at various frequencies to create the unlike notes of the instruments. By neutering the RC tour that we are feeding into the 555 timer, we can interchange the frequency of the output square wave to looseness different notes. All of the instrument circuits are fundamentally the same. They sporty expend different means of changing the RC circuitry we are providing as an input. In these circuits, we will be using the 555 timers in astable and monostable configurations (more on this later).

Before we dive fully into the 555 timer, there are some fundamental construction blocks we indigence to understand. The first is a comparator shown in the red block and the yellow block. A comparator has ii inputs and i outturn. When the V+ stimulant is greater than the V- input (denoted with the bubble), it drives the output high pressure. When the V+ stimulus is inferior than the V- input, it drives the turnout low. There are two comparators inside the 555 timer circuitry. These comparators are used to wrench the yield of the 555 timer on or off supported the threshold value and the spark value.

The second electrical circuit component we need to understand is the SR (set-readjust) Reversal shown in the purple. The truth put over for the effectuation logic of the Sr thong is shown in the set back higher up. The SR flip-flop sets the state of the output supported the State of the comparators. The threshold comparator is connected to the Reset tholepin of the flip-flop and the touch off comparator is on to the Set pin of the change of mind.

The push-pull output number one wood shown in pink is used to source current for the output. The electronic transistor shown in blue is wont to connect the discharge oarlock to soil, typically to discharge an external capacitor. The 3 resistors shown in gullible are of equal value. They divide the supplying voltage, VCC, into 2/3 and 1/3 of its economic value. These values are used As the reference voltages for the comparators.

Although information technology looks complicated at first glance, the 555 timekeeper basically just charges and discharges an outside capacitor and toggles the output based along the nation of the capacitance. Starting out, the outward capacitor is discharged meaning that the trigger electromotive force is to a lesser degree 1/3 Vcc. This turns happening the trigger/localise comparator, driving the turnout high. The external condenser continues to file until information technology gets higher up 2/3 Vcc. At that point, the threshold/reset comparator turns connected, drive the end product down. The discharge transistor connects the external condenser to ground causing information technology to discharge. In one case the external capacitor drops below 1/3 Vcc, the entire process repeats finished and over again creating our neverending transparent wave.

In case information technology still doesn't get across, you can check out these simulations courtesy of Paul Falstad. I am a fairly visual scholar, so sighted circuit simulations in truth helps Pine Tree State understand what is going on in a circuit.

555 timer square wave simulation - http://web.falstad.com/circuit/e-555square.html

555 timekeeper internals pretending - http://www.falstad.com/circuit/e-555int.html

We will predominantly personify using the 555 timers in astable mode. This means the electrical circuit is Federal by an RC circuit and is free-linear to generate an output honest wave. The Atari Punk Console uses the first 555 timer in astable manner and the second 555 timer in monostable mode. Monostable mode means that it is fed away an external source and outputs a one-shot pulse. In the Atari Punk Cabinet, we are using an astable 555 timer to provide a indicate to the monostable 555 timer.

Step 2: Theremin

Now it's time to make your theremin! Instead of victimization proximity wish a typical theremin, this theremin uses light intensity to determine the note's oftenness. This theremin has two photoresistors in the RC circuit feeding the 555 timer circuit to touch the rank of charging/discharging of the capacitor. The underground of a photoresistor decreases every bit the fat-free intensity decreases pregnant the capacitance will admit longer to rouse and discharge. So by reducing the amount of light getting to your photoresistors, you reduce the absolute frequency being played. To increase the frequency, increase the thin saturation.

To build your theremin, start by placing the 555 timer chip on a breadboard. You can build the circuit any way you want. I typically start away placing components in sequential order start at pin 1 of the IC chip and moving complete the mode around to pin 8. Make for certain you place some distance 'tween your photoresistors so that you can control the amount of money of light getting to each photoresistor separately. Be diligent noting the polarity happening your capacitors and the speaker. R5 is a potentiometer that is used for bulk hold in.

Once you have built the electrical circuit, go around the IC from pin 1 to pin 8 again to double-check that everything is connected the right way. To confirm nothing is shorted, you can connect a multimeter 'tween pin 1 and pin 8 happening your 555 timekeeper. You should see a just amount of money of resistor between these ii points. Erstwhile you are sure everything is connected properly, you send away connect the 9V battery. Your theremin should start making randomness! If you don't pick up anything or the sound is faint, adjust R5 to finetune the volume to your liking.

Since the ambient candlepower can vary greatly based on where you are playing your theremin, you may have to swap out C3. If the oftenness set out on your theremin is too high inclined, try switching C3 for a capacitor with a slightly big electrical condenser value. If the frequency is too Low, prove a slightly lower value capacitor.

Whole step 3: Harmonium

Now it's time to make your electric organ! The Hammond organ uses a 555 timer lap in astable mode. The tactile switches are used to switch in different capacitors to determine the frequency of the tone that is played. You can add as many contrary switches and capacitors in parallel as you want. You can also combine them in concert by press two buttons or keys at the same metre (combining capacitors in parallel results in an like capacitance value equal to the sum of the two capacitances which will produce a complete that's frequency is lower than either of the two switches on their own).

To calculate the taxon tone of each of your keys, you crapper expend the next equation. R1 is active to Be the esteem of your potentiometer based on the position of the wiper and R2 is 10kOhm. C is the value of the capacitor that you are switch in. f is the sequent frequency in Hertz. 0.693 is the unbleached log of 2.

f = 1 / (0.693×C×(R1 + 2×R2))

As a starting maneuver, preceding is a table of some common capacitance values with their corresponding calculated frequencies assuming that R1 is 100 kOhm. Remember that if you don't have the verbatim capacitance value you are looking for, you can combine capacitors victimisation the following equations.

For capacitors in series: 1/C_equivalent = 1/C1 + 1/C2 + 1/C3

For capacitors in collimate: C_equivalent = C1 + C2 + C3

To more well figure out how you lav combine capacitors you already have to make over a specific capacitance value, check over this Instructable and try out my Equipped Resistor/Capacitor Par Calculator.

Build your harmonium in the same way you built your theremin. Start by placing the 555 timekeeper chip on the breadboard. Remember you need will deman to save a lot of blank for the pushbuttons. Start placing the rest of the components starting time with the parts connected to pin 1 of the IC and moving all the agency just about to pin 8. I placed the buttons and their related capacitors after connecting everything else.

Be careful noting the sign on your capacitors and the speaker. As before, double-check the circuit and substantiate zilch is shorted. Once you are sure everything is connected properly, you can connect the 9V battery. Press the keys and your organ should start playacting! If you don't hear anything or the sound is faint, adjust R3 to finetune the volume to your liking.

Step 4: Atari Punk Console

Straight off it's time to make your Atari Punk Cabinet! The Atari Punk Console (APC) is essentially an astable 555 timer electrical circuit generating a square wave to aim a monostable 555 timer circuit which creates a unique square pulse. There are two potentiometers for operate: one for the oftenness of the oscillator (R2) and one for the pulse breadth (R3). The APC is thoughtful one of the most iconic simple DIY synthesizers.

Build your Atari Punk Cabinet in the like room you well-stacked your other instruments. I would get down by building the racing circuit for the first 555 timer (U1) before hurling on to the irregular 555 timer (U2). Start placing the rest of the components beginning with the parts connected to pin 1 of the IC and moving all the way around to pin 8. Erstwhile you throw finished the circuitry surrounding U1, add U2 to the board and build the circuitry surrounding U2.

As before, exist unhurried noting the polarity connected your capacitors and the speaker. Double-confirmation the circuit and confirm nix is shorted. In one case you are sure everything is neighboring properly, you can connect the 9V battery. Your APC should start playing! Start twisting the frequency and pulse-width knobs and playacting your very own synthesizer. If you don't hear anything or the sound is faint, adjust R4 to finetune the volume to your liking.

Step 5: Battle! Remix!

Now you've got all three instruments and you're fit to assemble your band! In my class, I gave about a twenty-four hour period and a half to go through the 555 timer, ramp up the circuits, assemble bands, come dormy with a name and logo, write songs, and prepare a performance. The end result was a parcel out of fun. In that location were bands with perfectly tuned instruments who played well-nig-perfect renditions of "Lavender Township" and other bands who went with to a greater extent of a free jazz, improvisational approach. All-in-all, these are really amusive circuits for anyone at any level to play around with.

You can also render remixing these circuits even more! Try swapping the potentiometers in the APC for photoresistors. Try combining the organ or theremin with the second stage of the APC. Strain using thermistors Oregon pressing-delicate resistors in situ of the photoresistors. Hear using fixed resistors and variable capacitors instead of fixed capacitors and variable resistors. There are so many several directions you can take these instruments. Rich person fun!

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