Two-Tone Phototransistor Theremin Using a 556 Timer IC

Transcription

1 Two-Tone Phototransistor Theremin Using a 556 Timer IC BY CABE ATWELL Difficulty: Easy - Medium Build Time: 2-3 hours The Theremin is an electronic musical instrument with its roots in the dark world of espionage. It was the year In the new Soviet Union, the Russian physicist Lev Sergeyevich Termen (aka Léon Theremin) was tasked with researching proximity sensors that could detect a human body. He used high-frequency electromagnetic oscillations and created the radio watchman, a device that changes the pitch of a tone based on the proximity of a body. Vladimir Lenin, the Bolshevik leader, was impressed by the device. He even took lessons on how to use it as a musical instrument. Lenin sent Léon Theremin around the world to demonstrate the Theremin. Eventually, Theremin ended up in the USA, in 1928, where he patented the device. Electronic music was born! Flash forward ninety years, and the Theremin is a standard instrument around the globe. The sound a Theremin produces a spooky weeeeeeee-oooooooh sound heard in a lot of science fiction and horror movies can be mimicked by today s synthesizers. Even the contactless interfacing can be reproduced in other ways, and inexpensively too. This project will attempt to make the simplest version of a contactless theremin-like tone-producing device. At the heart of this project is a 556 timer integrated circuit (IC). This particular IC technically consists of two separate 555 timer IC circuits on a single chip. Each side of the 556 timer here, in this project, will produce a different tone. One low and one higher pitched. The circuit configuration places both sides of the 556 timer into astable mode. In other words, the 556 timers will generate wave forms at certain frequencies. If the frequency is in a particular range, it can be heard through the speaker. In other words, the regularity of the waveform will generate a sound tone. In this device, the tones are changed using phototransistors in a particular configuration. Phototransistors sense how much light surrounds them, and they change electrical properties as the lighting changes. This effect will be harnessed to create a highly sensitive interface for the tone generators on the 556 timer. First, let s take a look at the schematic.

2 2 What is happening here is a precise controlling of the 556 timer. The resistor labeled R1 and the phototransistors on the left side, and R2 and the phototransistors on the right side, control how long the output pulses are on and off for either side of the 556 IC. The phototransistors in their configuration are acting like a variable resistor. Typically, a transistor controls the current flow between the emitter and collector depending on the current applied to the base. The base current, in this case, is being changed by the light level. Hence, the emitter-to-collector current changes. Since there are two transistors configured opposite to each other, the current can flow in both directions. The output pulses from the 556 are also known as Positive and Negative Time Intervals the time the pulses are in the on and off state respectively. The total time between pulses is the positive (on) and the negative (off) time intervals added together, also known as the frequency of the sound. The ratio between the resistor and the effective resistance of the transistors can be seen in this equation: Frequency = 1.4/((R1+2Rt)/C1) (Where Rt is the equivalent resistance of the phototransistor leg) As you wave your hands and fingers over the device, the amount of light falling on the phototransistors will change. This changes the value of Rt, which changes the frequency of the 556 chip, which changes the sound you hear.

3 To build this project, a handful of items will be needed: 556 Timer IC (Jameco part number 24329) 10k Ohm resistor (Jameco part number ) 47k Ohm resistor (Jameco part number ) 2x 1M Ohm resistor (Jameco part number ) 2x 0.22 μf(220 nf) ceramic capacitors (Jameco part number 25540) 2x 50 μf electrolytic capacitors (Jameco part number ) 4x Phototransistors (Jameco part number ) 2x 8 Ohm speaker (Jameco part number OR ) Breadboard Wire kit (Jameco part number ) 1x full-size breadboard (Jameco part number 20723) 3 When assembled on a breadboard, the project will look something like the above image. Exact wire color or length isn t important. As long as all the points are connected, then everything will work.

4 01 01 TAKE THE BREADBOARD AND 556 TIMER IC AND PLACE THEM ON AN ANTI-STATIC SURFACE IF THERE IS ONE AVAILABLE. PLUG THE IC INTO THE BREADBOARD. THE LITTLE DIMPLE IN THE CHIP SHOULD BE FACING THE LEFT. IN THIS CONFIGURATION, THE PINS ON THE CHIP ARE LABELED 1 TO 7 FROM LEFT TO RIGHT ALONG THE BOT- TOM, AND 8-14 FROM RIGHT TO LEFT ALONG THE TOP CONNECT THE POSITIVE RAIL ON THE BREADBOARD TO PIN 14 (VCC) ON THE CHIP (TRADITIONALLY, THIS USES A RED JUMPER WIRE). THEN CONNECT THE NEGATIVE RAIL ON THE BREADBOARD TO PIN 7 (GND) WITH THE BLACK WIRE CONNECT PIN 4 AND PIN 10 (BOTH RESET) DIRECTLY TO THEIR RESPECTIVE POSITIVE POWER RAILS.

5 04 04 CONNECT THE TOP AND BOTTOM POWER RAILS TOGETHER POSITIVE TO POSITIVE AND NEGATIVE TO NEGATIVE TAKE THE TWO 1M OHM RESISTORS AND CUT THE LEADS A BIT SHORTER, AS SHOWN. THIS WILL ENSURE THE COMPONENTS WILL STAY CLOSER TO THE BREADBOARD S SURFACE. IT LOOKS A LOT NEATER THIS WAY, AND PIECES ARE LESS LIKELY TO BREAK OFF THE BREADBOARD USE A SMALL JUMPER TO CONNECT PIN 2 TO PIN 6, AND PIN 8 TO PIN 12. INSERT THE 1M OHM RESISTORS AS SHOWN, CONNECTING PINS 6 AND 8 TO THE NEGATIVE POWER RAIL TRIM THE LEADS OF THE 47μF ELECTROLYTIC CAPAC- ITORS. YOU LL ALWAYS BE ABLE TO TELL WHICH SIDE OF THE CAPACITOR IS WHICH THE NEGATIVE LEAD IS INDICATED WITH A STRIPE AND NEGATIVE SYMBOLS.

6 08 08 CONNECT THE 47μF ELECTROLYTIC CAPACITORS AS SHOWN. THEY ARE PLACED THIS WAY FOR LATER EASE IN THE BUILD CONNECT THE POSITIVE LEADS OF THE CAPAC- ITORS TO PINS 5 AND 9 RESPECTIVELY THE PHOTOTRANSISTORS ARE NEXT. DO NOT TRIM THEIR LEADS. THEIR ORIEN- TATIONS ARE INDICATED BY ONE LONG LEAD AND ONE SHORT. THEIR LEADS NEED TO BE PLUGGED INTO THE BREADBOARD INVERSELY TO EACH OTHER SO, ONE SHORT AND ONE LONG LEAD IN THE TOP COLUMN OF THE BREAD- BOARD, AND ONE SHORT AND LONG LEAD CON- NECTED IN THE BOTTOM COLUMN.

7 12 12 ADD A 47K OHM RESIS- TOR CONNECTING THE POSITIVE POWER RAIL TO ABOUT HERE THE 0.22 μf CERAMIC CAPACITORS HAVE NO POLARIZATION, SO ORIENTATION OF A POS- ITIVE AND NEGATIVE SIDE ISN T AN ISSUE THEN CONNECT ONE LEG TO THE BOTTOM OF THE PHOTOTRANSISTOR COL- UMN, AND THE OTHER LEG TO THE NEGATIVE POWER RAIL. ALSO CONNECT THE RESISTOR TO THE TOP OF THE PHOTOTRANSISTORS CONNECT PIN 1 ON THE 556 TO THE RESISTOR. HERE, WE SHOW YOU HOW TO DO IT WITH SMALL HOPS OF WIRE, TO CREATE A LOW- ER-PROFILE WIRE BUILD ON A BREADBOARD. OF COURSE, YOU CAN ALWAYS CONNECT A SINGLE LONG WIRE DIRECTLY FROM PIN 1 TO THE RESISTOR.

8 16 16 CONNECT PIN 2 ON THE 556 TIMER IC TO THE LEFT PIN ON THE CAPACITOR. HERE WE RE USING A SINGLE LONG WIRE. DO NOT CONNECT PIN 2 TO THE OTHER PIN ON THE CAPACITOR; THE CIRCUIT WILL NOT WORK THAT WAY DO THE SAME BUILD ON THE RIGHT SIDE OF THE BREADBOARD. NOTE: THE RESISTOR ON THIS SIDE OF THE CIRCUIT IS THE 10K OHM RESISTOR, AND IT IS CON- NECTED TO PIN 13 ON THE 556 TIMER CHIP THE RIGHT SIDE OF THIS CAPACITOR SHOULD BE CONNECTED TO PIN PLUG THE POSITIVE LEADS OF THE TWO 8 OHM SPEAKERS INTO THE NEGATIVE SIDE OF EACH OF THE 47 μf ELECTROLYTIC CAPACITORS. THEN CONNECT THE SPEAKER GROUND TO THE BREADBOARD NEGATIVE POWER RAIL.

9 20 20 CONNECT THE POWER TO THE POSITIVE AND NEGATIVE RAILS. 9 THE PROJECT WILL IMMEDIATELY START MAKING A SOUND. THE LEFT SPEAKER, AND LEFT SIDE OF THE BOARD, WILL PLAY THE LOWER-PITCHED TONE. THE RIGHT SIDE WILL PLAY THE HIGHER-PITCHED SOUND. CAREFULLY MOVE YOUR HANDS AND FINGERS OVER THE PHOTOTRANSISTORS TO BLOCK LIGHT, AND THE SOUNDS WILL CHANGE. ALTERNATIVELY, GET A FLASHLIGHT AND SHINE IT ON THE PHOTOTRANSISTORS. THE SOUNDS WILL CHANGE DEPENDING ON THE LIGHT INTENSITY.