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Constructing a Cassette Tape Pitch Mod with a Raspberry Pi Pico
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Tape decks and pitch mods
Again within the 1980’s and 90’s, cassette tapes had been the first method individuals would take pleasure in music each at house and on the go. They work by having a pair of spools with magnetic tape wound round one aspect at the beginning, then slowly unwinding it throughout a head that reads the info saved on the tape’s floor. Usually, this all occurs at only a single velocity, that means that for these wanting a gradual, ambient sound have to by some means alter the drive motor’s rotational velocity. In response, individuals have been including pitch mods, which frequently use a potentiometer or perhaps a single swap that slows down the motor, though it may be tedious to manually alter over time. Isaac Thomas had the thought to make his personal model that makes use of a microcontroller to fluctuate the velocity, leading to a nicer, automated system.
Driving the motor
For this to work, Thomas selected to make use of a Raspberry Pi Pico, which relies on the customized RP2040 chip. The Pico was then linked to a MOSFET driver that’s, in flip, managed by a PWM sign from a digital GPIO pin. In comparison with the traditional potentiometer, PWM is only digital slightly than analog, and it simulates analog voltages by quickly toggling on and off inside a set frequency. This quantity of “on” time inside one interval is known as the “obligation cycle”, and for example, setting the obligation cycle to 50% with a voltage of three.3v leads to an approximate voltage of 1.65v. So every time the Pico needs to hurry up the motor, it raises the obligation cycle, which causes the MOSFET to permit extra energy to move to the motor.
Making a sequencer
After establishing the drive management mechanism, Thomas then wanted a strategy to enter the varied parameters required for his sequencer. To do that, a rotary encoder was added which lets customers flip a dial to do all the things from altering the tempo, setting sound values, and selectively muting notes. In the meantime, all of this knowledge may be simply seen on a single 128×64 OLED display that communicates with the Pico over the I2C bus. The ultimate step concerned enjoying a tape containing a pure 1kHz sine wave after which analyzing how the obligation cycle maps to it when the velocity modifications over time. Selectively muting notes was performed by constructing a DIY optocoupler and putting it inline with the sound amplification circuitry. When the LED is turned on, the photoresistor’s resistance is lowered and permits present to cross by way of, and vice-versa.
Meeting and future plans
At the moment, all the electronics match right into a small cardboard field that holds the breadboard and energy converter in place. The lid has two 3.5mm jacks that result in the cassette participant whereas the rotary encoder and display sit close to the underside. Sooner or later, Thomas plans to incorporate a MIDI enter circuit for studying velocity knowledge in addition to a management voltage (CV) enter for adjusting playback velocity.
To see extra about this venture, you possibly can learn its write-up right here on Instructables or watch its demonstration video beneath.
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