The objective of this project was to design and develop an electronic product from the ground up as part of an electronic product development course. It focuses on creating an electronic piano with eight keys (C middle to C'), adhering to a component cost limit of 20 Hong Kong Dollars and dimensional constraints of 18cm x 10cm x 6cm (final design: 16cm x 9cm x 5.5cm, ~350g).
The course covered basic components and their connections, with guidance on tools like PADS-Logic for schematics, PADS-Layout for PCB design, and SolidWorks for the 3D casing. Features were prototyped on a breadboard before final PCB implementation. Weekly progress was documented for feedback from instructor Ms. NGAN Lai Yin.
This piano targets children and hobbyists as an affordable alternative to high-end instruments, enabling home practice. It demonstrates skills in circuit design, PCB fabrication, and enclosure modeling.
Product Specifications- Power Supply: Dual options—6V battery pack (inside case, replaceable) or micro-USB. Switches for on/off and source selection; LED indicator for status.
- Audio Keys: 8 push buttons for notes C (261.6 Hz), D (293.7 Hz), E (329.6 Hz), F (349.2 Hz), G (392.0 Hz), A (440.0 Hz), B (493.9 Hz), C' (523.3 Hz). Frequencies detailed in Circuit Design Principles.
Musical Note
Frequency (Hz)
R_b (kΩ)
Resistor to Achie
- Audio Output: Built-in 0.5W speaker; 3.5mm jack for headphones to avoid disturbing others.
- Volume Control: Potentiometer for smooth, linear adjustment of speaker/jack output.
- Vibrato Effect: Slide switch to enable/disable; potentiometer adjusts modulation frequency (1-20 Hz) for pitch variation.
- Product Details: Portable (350g), user-friendly for kids; dual power enhances versatility.
Schematic DiagramThe schematic was designed in PADS-Logic, illustrating all component connections for easy prototyping and PCB fabrication.This clarity ensured accurate implementation.
Circuit Design PrinciplesThe circuit uses an NE556 IC as an astable multivibrator for audio signals. Frequency is calculated via:
Circuit Design PrinciplesThe circuit uses an NE556 IC as an astable multivibrator for audio signals. Frequency is calculated via:
Resistors are in series; pressing a button sums R_b in the loop. Emphasis was on low-cost, available components: dual power with diodes for protection, NE556's second timer for vibrato, LM386 for efficient amplification, and tact switches for reliable contact.
VibratoEffect
The vibrato uses the NE556's second timer as a Low Frequency Oscillator (LFO) connected to the first timer's control pin.Default (grounded): Stable 2/3 Vcc reference for consistent frequency.LFO connected: Voltage fluctuates, varying capacitor charge time for pitch "wobble" (higher/lower frequency moments). Adjustable via 100kΩ potentiometer for 1-20 Hz rate. This maximizes NE556 utility without extra costs.
Cost EstimatesComponents total: 16.28 HKD (bulk estimates, lab-available). PCB printing: 65.49 HKD (incl. shipping). 3D case printing: 113.36 HKD (incl. shipping). All under budget constraints.
PCB LayoutDesigned in PADS-Layout with auto-routing in PADS-Router. Fits size limits; verified against schematic.
Case DrawingsThe case designing was done using SolidWorks software. To ensure the components such as variable resistors, tact switches, LED and other components fitted properly on the casing, digital vernier callipers were used to take measurements of the components. Moreover, image of the PCB was imported as a sketch image to the SolidWorks design to further ensure consistency.
Back Lid for enclosure of PCB and battery
Components fit with tolerance; PCB screwed to front lid, battery glued to back. Auto-locking screws for child safety; soldered connections minimize issues.
This project showcases end-to-end design: NE556/LM386 circuits, PCB/enclosure fabrication, testing. It meets specs affordably, building skills for future work.
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