Named after its creator, the theremin originated in the Soviet Union in the beginning of 1920's. This comprised of a container installed with a couple of antennas. It did not have any keyboard to play, no strings like in guitars. Rather, the theremin made use of human body capacitance to manipulate the volume and the pitch and of the output musical signal. The operator just had to wave his or her arms close to the antennas to generate a correspondingly varying musical tone!
Contributed by Ragini Sharma
Early Applications
The most significant application of the theremin has been in an uncounted variety of low budget horror movies. The spooky strooling noises heard in those movies during many actions were actually created from a theremin device.
Likewise, They have also been used in many pop and rock music concerts. Although the the first theremin made use of a couple of antennas and a variety of pipes and tuned circuits, replacing them with modern integrated circuits makes the work drastically simpler.
How much will it Cost?
In this post, we'll learn the development of a straightforward theremin with components that may be worth less than $5. Electronic enthusiasts having a junkbox full of components might manage to get the job done for possibly a lower cost.
The theremin is effortlessly put together and applied, even by individuals with no musical qualifications. On top of that, the theremin could be loads of enjoyment, particularly at Halloween celebrations!
In this circuit, the pipes and LC circuits are actually changed with a couple of low-cost and readily available IC's, to generate the proposed Digital Theremin.
Understanding the Block Diagram
A block diagram of the circuit can be found in the following in Fig. 1.
The Theremin works with a set of two high frequency oscillators for functioning. One of these oscillators funtions with a constant frequency, while the other is variable through the body capacitance of the operator.
The frequency generated from the two oscillators are combined through an exclusive circuit called the balanced modulator.
The balanced modulator attenuates the initial signals and generates a complicated transmission which includes the sum and difference frequencies in the two inputs.
When one particular oscillator is performing at 100 kHz and the second one at 101 kHz, we will get an output constituting a pair of frequencies at 201 kHz and 1 kHz.
Because the higher range of human ability to hear is restricted to 20 kHz or so at the most, only the 1 kHz difference frequency will be hearable due to the influence of the balanced modulator connected before an audio amplifier.
How the Circuit Works
The schematic picture for our Digital Theremin is demonstrated in the above figure.
U1 could be either a CD4069 or 74C04 hex inverter, it is used like a constant frequency oscillator fixed around 100 kHz.
IC U2 includes the variable frequency oscillator and balanced modulator to accomplish the remaining portion of the circuit.
The CD4046 is a phase-locked-loop configuration and had been initially created for frequency multiplier type applications. However, its components fulfills our requirements flawlessly.
R3, R4. and C2 establish the center frequency of the built in oscillator chip. The antenna creates a parallel capacitance together with C2, that enables the frequency to get changed many kilohertz when a human hand approaches the antenna.
The ZERO control resitor implemented by R4, makes it possible for the variable oscillator to be fixed at the identical frequency equal to the fixed oscillator.
If the difference frequency is under 15 Hz, it is under the lower frequency threshold of our hearing range.
By tweaking the two oscillators for the identical frequency, the Theremin stays muted until the operator or the performer moves his or her hand close to the antenna.
The frequencies created by the two oscillators are combined by an exclusive OR gate within the IC 4046.
This gate works like a digital balanced modulator, that creates the sum and difference frequencies as discussed previously. The OR gate output is subsequently AC coupled through C3 with LEVEL control resistor R5 and an output jack for a quick integration with an external audio amplifier. A 9 V PP3 battery can be used for powering the circuit.
PCB Designs
It is a simple circuit and could be assembled with a 2x2-in PCB . A track layout for the printed circuit board of Theremin as displayed in figure below:
One important aspect is that the Theremin must be mounted into a metal case only, since the metal forms a shield that greatly eliminates the potential for the oscillators to change in frequency.
Having the metal case enables the theremin far simpler to calibrate.
C1 and C2 both need to be silver mica capacitors for optimal outcomes, ideally with a tolerance of ± 5 per cent.
Since both chips are CMOS it is highly recommended to incorporate IC sockets. Apart from that, the board 's layout and assembly is uncritical.
Once the project is finished, we have to work with installing the antenna and attaching it to the board.
Because the antenna is protected with a fine coating of chrome, it isn't possible to solder a wire effectively to the antenna on its own. Just connect a small piece of wire to one of the washers and attach it to a 2-56 machine screw and bolt antenna (see Figure 5).
Calibration and Testing
Upon completion of assembly, closely check the Theremin for defects in the interconnects, weak solder joints and other possible issues. If everything looks perfect, connect the Theremin with a cord up to an audio amplifier, add a battery to the device, and switch it ON.
Slowly and gradually increase the volume with the LEVEL control. If everything works correctly, you might be suceessful in hearing a high-pitched squeal. Now, waving your hand close to the antenna should cause the pitch of the sound to boost. Try increasing the antenna length to its full capacity and fine-tune the ZERO control knob to identify a sweet spot where a dead zone or null-spot is noticed until of course your hand is brought near the antenna.
Troubleshooting the Circuit
In case the squeal fails to arrive at any tuned spot, try making the antenna shorter by a few inches and give it a try again.
Once the setting up is implemented accurately, the Theremin should keep muted until the operator waves his or her hands within a few inches from the antenna.
You may come across numerous aspects influencing the human body capacitance, and all of these could affect the Theremin's efficiency level.
Aspects such as the antenna length, air moisture, the size, and operator's costume, and the shoe sole resistance to ground could all influence to warrant an alteration in the ZERO control adjustments.
Through some practice, the ZERO control could be appropriately set in a matter of seconds.
Lastly, the Theremin must be offered a few minutes to become stable, on account of temperature variations, soon after the supply voltage is initially switched on.
When the Theremin is energized and right away zeroed, it will likely cause the tuning to drift and demand a re-calibration repeatedly.
The most effective remedy would be to switch the power on using the LEVEL control completely down, and provide the Theremin several minutes or so to warm up before calibrating the ZERO control.
Conclusion
The Theremin works naturally and with special audio effects.
A volume pedal enables you to bring dynamics and introduce fadeouts, and nearly any of the ground device for guitarists or synthesizers may alter a few element of the sound quality.
The ethereal sound of the Theremin performs wonderfully using echo and delay enhancements.
Regardless of whether the Theremin is employed like a special effect generator for rock groups or cinema organizations, or simply to enrich your future Halloween celebration, you will discover that this gadget can provide you with lots of unconventional sound effects using a incredibly humble expenditure in terms of time or money.
Not only is the Theremin fascinating and informative, is actually great fun!
Parts list
C1,C2 - 51pF, silver mica capacitor
C3 - 1nF, 25-WVDC electrolytic capacitor
C4 - 220pF, 25-WVDC electrolytic capacitor
R1 - 1M, 1/4 -watt. 5% resistor
R2, R3 -100k, 1/4 -watt, 5% resistor
R4 -10k, linear potentiometer
R5 -10k, audio potentiometer
R6 - 47-ohm, 1/4 -watt, 5% resistor
U1 - IC 4069 or IC 74C04 CMOS hex inverter/buffer, integrated circuit
U2 - IC 4046 phase-locked loop, integrated circuit
ADDITIONAL PARTS AND MATERIALS
Printed -circuit or perfboard materials, general-purpose replacement antenna aluminum case, IC sockets, 9 -volt transistor -radio battery, 9 -volt -battery clip, wire, solder, hardware, etching solution (if needed), etc.
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