SmartPiggy: A goal-based savings companion for kids
This project explores a Smart Piggy bank System that goes beyond traditional saving to teach children how to save with purpose. While conventional piggy banks and school-led saving schemes encourage putting money aside, they rarely guide children on how to save strategically toward a goal. This project seeks to bridge that gap.
Inspired by how children learn arithmetic through everyday actions like adding coins or calculating change, this concept introduces structured, goal-based saving through interaction. The piggy bank functions as a mini banking system, internally organizing deposited coins to make savings visible and purposeful.
I am currently working with two conceptual approaches. The first is a goal-based model where a child sets a specific savings target and receives weekly guidance on how much to save. The second draws from the simplified 50-30-20 principle, where only a portion of the saved amount is accessible, encouraging discipline and delayed gratification. By combining saving with intention and planning, the piggy bank becomes an active learning tool rather than a passive container.
Concept & Rationale
Children are often told to save money, but rarely taught how to save wisely. Many accumulate coins without a clear purpose, leading to impulsive spending once the money is accessed. This pattern often continues into adulthood. I observed similar contrasts among colleagues on the same payroll-some struggled before month-end, while others managed comfortably. This raised a key question: why does saving feel intuitive for some, but not for others?
This reflection led to the idea of teaching children not just to save, but to save with intention.
In India, physical coin saving is becoming increasingly rare. UPI has made transactions invisible, fast, frictionless, and abstract. But for a child learning about money for the first time, that abstraction is a problem. The weight of a coin, the sound of it dropping, the deliberate act of choosing and depositing, these physical moments make money real in a way a UPI transaction never can.
Designing for the Senses
I've noticed that the things children engage with most deeply are rarely the ones that look the most impressive, they're the ones that feel the most alive. The ones that respond, that make sounds, that change when you interact with them.
There's a reason for that. The more senses involved in an action, the more intuitive it feels, the more it holds attention, and the more it is remembered. A single tap on a screen engages almost nothing. But dropping a coin into a slot - feeling its weight, hearing it fall, pressing a button, watching a light change, hearing a voice respond - that's five distinct sensory moments from one small act.
SmartPiggy is deliberately designed around this. Every coin deposit is a multisensory experience:
Touch - the weight of the coin, the press of a button
Sound - the coin dropping, the servo opening, the voice feedback
Sight - the progress lights filling up, the celebration flash at milestones
Action & Response - the flap physically opening only after the child makes a choice
This isn't decoration. Each sensory layer reinforces the intention behind the action - you chose to save, the system acknowledged it, and something in the world changed because of you.
That feeling of consequence is what makes saving feel real.
SmartPiggy is built around that physicality. The interaction is intentional, not incidental.
The Smart Piggy Bank introduces goal-oriented saving, where a child sets a specific target (with parental guidance) and works toward it through consistent contributions and delayed access to funds. Saving becomes a structured and intentional process rather than simple accumulation.
Through this process, the child learns:
- Restraint and patience
- Delayed gratification
- Foundational financial awareness
- An understanding of planning over impulsive spending
To reinforce positive saving behavior, the Smart Mini Bank rewards the child upon successful completion of a goal by adding a small amount of interest to the saved total, introducing simplified real-world financial principles in an age-appropriate manner. Parents act as facilitators rather than enforcers, guiding reflection and discussion instead of merely controlling access to money.
At its core, this project reimagines the traditional piggy bank as a Smart Piggy Bank, an interactive system that encourages purposeful saving and helps children develop a healthy, intentional relationship with money from an early age.
Vision Statement: Making mundane things interesting. Saving, but fun, intentional, rewarding, encouraging, motivating, with a real sense of achievement.
Initial concept model on SketchUp
I began with a more architectural approach, where the piggy bank was imagined as a small enclosure. It felt structured and system-driven, almost like a miniature building that housed interactions.
Later, while exploring form in Blender, I moved towards a more familiar and approachable object, a piggy. This shifted the direction. The object started to feel less like a device and more like something a child would naturally engage with.
Now, I am thinking of bringing both these directions together.
The outer form will remain that of a traditional piggy bank, soft and recognizable. At the same time, it will carry elements from the earlier enclosure idea. Buttons and a small display will sit on the surface, making the interaction visible and intentional.
Inside, the system remains structured. A defined coin chamber, the PCB, and the sensing mechanisms are all contained within. So while the outside feels simple and friendly, the inside holds the logic and complexity of the system. It becomes a combination of familiarity and function.
Why a Pig?
While working on this project, a question struck me:
Why are piggy banks shaped like pigs? Why not a Platypus, or an Ostrich, or anything else?
It turns out, it's a happy accident of language. In medieval Europe, a cheap orange clay used to make household pots and jars was called pygg. People stored spare coins in these everyday vessels, which came to be known as pygg pots or pygg banks. Over centuries, as the clay fell out of use, the word remained - and by the time potters were receiving orders for "pygg banks," many had forgotten the material origin entirely. So they did the logical thing: they made them shaped like a pig.The iconic piggy bank was born from a misunderstanding, not intention.
MiniBank – Final Project Development Plan
To organize the development of the MiniBank system, the project is structured into a series of stages covering research, system design, electronics development, fabrication, and integration. The following table outlines the planned workflow and expected outputs for each stage.
| Stage | Activity | Purpose | Output |
|---|---|---|---|
| Concept Exploration | Initial idea of a coin sorting system based on the 50–30–20 money management model | Explore how physical coin allocation could support financial learning | Early concept sketches |
| Concept Refinement | Shift from mechanical coin sorting to goal-based saving | Align the system with behavioral learning objectives for children | Revised project direction |
| Context Research | Study variations in Indian coin diameter, thickness, and materials | Evaluate feasibility of physical denomination detection | Coin comparison dataset |
| Sensor Exploration | Investigate detection approaches including mechanical slots, IR sensing, load cells, and inductive sensing | Understand technical trade-offs between sensing methods | Sensor feasibility analysis |
| System Scope Definition | Analyze coin validation methods used in vending machines and banking systems | Define practical system boundaries appropriate for the project | Defined detection strategy and project scope |
| Interaction Design | Develop behavioral reinforcement model with micro rewards and milestone celebrations | Create a motivating saving experience for children | Interaction and reward system framework |
| System Architecture | Define input devices, processing unit, and output components | Translate the concept into a structured electronic system | System block diagram |
| Electronics Learning | Study PCB design workflow including schematic creation, component placement, and trace routing | Understand how to design and fabricate a custom PCB for the MiniBank electronics system | Foundational PCB design knowledge |
| Electronics Development | Design circuit connecting sensors, NeoPixel LEDs, servo motor, buzzer, and display | Create the hardware platform for the interactive system | Schematic and PCB layout |
| Mechanical Design | Design piggy bank enclosure and internal coin path | Integrate electronics with the physical structure | 3D CAD model of enclosure |
| Fabrication | Manufacture enclosure components using CNC or laser cutting | Produce the physical structure of the MiniBank | Fabricated enclosure components |
| Firmware Development | Implement coin detection logic, savings tracking, and milestone feedback | Enable interactive system behavior | Microcontroller program |
| System Integration | Assemble electronics, enclosure, and firmware | Validate complete system functionality | Working MiniBank prototype |
| Documentation | Record design decisions, experiments, fabrication processes, and results | Provide evidence of development and learning | Final project documentation |
Final Project Thinking Progression
Stage 1 - Coin Sorting for Money Management Training
My initial concept was to design a coin sorting system based on the 50-30-20 money management model. The idea was to:
At this stage, I was thinking mechanically:
However, while mapping this idea to the real objective, I realized: The project is not about managing spending categories. It is about goal-based saving for children. Sorting coins added:
This week helped me identify a mismatch between concept and purpose.
I decided to pivot.
Stage 2 - Shift to Goal-Based Digital Value Tracking
The project evolved from physical sorting to digital value accumulation.
New system requirement:
Detect coin → identify denomination → update total → display goal progress.
This was a conceptual shift from mechanical organization to intelligent tracking.
To implement this, I studied Indian coin characteristics:
I discovered that Indian coins are not standardized in a simple way. Different issues of the same denomination vary in material and design. This made denomination detection more complex than expected. This week was about understanding the physical reality of the problem.
Preliminary Diameter and Material Study for Coin Identification System Design
Since my final project involves designing a coin identification system that detects denomination and updates a running total, it was necessary to analyze whether Indian coin denominations are dimensionally consistent across different series. Accurate value computation depends on reliable physical identification; therefore, I first examined variations in diameter and material among commonly circulated coins.
Comparison across models
Final Comparison Summary
| Denomination | No. of Varieties | Diameter Range | Materials Used |
|---|---|---|---|
| ₹1 | 5 | 20–25 mm | Stainless Steel |
| ₹2 | 5 | 23–27 mm | Copper-Nickel, Stainless Steel |
| ₹5 | 5 | 23–25 mm | Copper-Nickel, Stainless Steel, Nickel-Brass |
| ₹10 | 3 | 27 mm | Bimetallic (Cu-Ni + Al-Bronze) |
| ₹20 | 1 | 27 mm | Bimetallic (Ni-Brass + Ni-Silver) |
Stage 3 - Understanding Different Sensors & Engineering Trade-offs
After studying the physical parameters of Indian coins, I moved into exploring different sensing mechanisms that could help identify denominations.
At this stage, I was not comparing industrial systems.
I was simply trying to understand:
What sensing approach is technically possible and practical for my context?
Since the project operates in a controlled environment and processes one coin at a time, I evaluated different sensors based on feasibility, complexity, and reliability.
Diameter Detection (Mechanical / Optical)
Measuring the width of the coin either through fixed mechanical slots or using optical sensors (such as IR break-beam) placed at defined spacing.
What This Is: A plate or ramp with multiple slots of different widths.
Each slot is calibrated to a specific diameter.
How It Works:
Limitation: Once fabricated, it cannot adapt. If coin size changes, redesign is required. This is purely mechanical detection, no electronics involved.
What This Is: An IR LED on one side and a receiver on the other.
When coin blocks the beam → signal changes.
What It Detects:
What This Is: Two IR beams placed a fixed distance apart.
How It Works:
Case 1 – Small coin:
Case 2 – Larger coin:
Microcontroller reads:
This allows approximate size classification without physical slot filtering.
Load Cell (Weight-Based Detection)
A load cell measures force using strain gauges. When a coin is placed on it, slight deformation generates a measurable electrical signal.
Why it could work:
Limitations:
IR-Based Detection Methods
IR Break-Beam Sensor (Object Detection)
What it is: An infrared LED (transmitter) and an infrared receiver placed opposite each other. The transmitter continuously emits invisible IR light toward the receiver.
How it works:
What it detects: Only presence of an object. Use in this project:Can detect coin insertion event reliably.
Limitation: Does not provide size or denomination information unless combined with additional logic.
IR Timing Analysis (Using Break-Beam Sensor)
What it is: A software-based method using the same IR break-beam sensor. Instead of only detecting interruption, the system measures: How long the beam remains blocked.
How it works: Coin enters → beam blocked → timer starts.
Coin exits → beam restored → timer stops.
Duration of blockage correlates to coin diameter (if insertion speed is controlled).
What it detects: Presence + approximate size.
Use in this project: Could help differentiate denominations based on interruption time.
Limitation: Highly dependent on insertion speed and user handling. Inconsistent movement may reduce reliability.
Inductive Sensing
What it is: A coil generates a magnetic field. When a metal object passes through it, the inductance changes depending on material properties.
Why it could work:
Limitations:
This method is technically strong but increases system complexity significantly.
Magnetic Response Detection
What it is: Using a Hall sensor or magnet to detect ferromagnetic properties of coins.
How It Works in Coin Detection
If a coin has ferromagnetic properties:
Limitations:
This would only work as a supporting parameter.
Insight
No sensing method is perfect on its own. Each approach introduces trade-offs between:
Stage 4 - Learning from Vending Machines & Banks
I researched how real systems handle coin validation.
Findings:Industrial systems use multi-parameter validation, combining:
- Diameter
- Thickness
- Electromagnetic signature
- Magnetic properties
- Optical timing
Important realization:Real-world systems never rely on a single parameter. However, their priorities differ:
- Banks focus on authentication and counterfeit detection.
- Vending machines focus on transaction reliability.
- My project focuses on behavioral learning and goal tracking.
This comparison helped me clearly define boundaries.My system does not need:
- Anti-counterfeit security
- High-speed processing
- Industrial-grade validation
It needs:Reliable detection within a controlled environment. This week was about defining scope.
Stage 5 - Project Direction
Inspiration - JumpStart 1st Grade (1995)
A childhood favourite, a vending machine mini-game where you identify coin denominations, insert them, and watch the machine tally up to the item price. Simple, satisfying, and surprisingly effective at teaching money recognition without feeling like a lesson.
This project borrows that same core loop, with one key difference:
| State | Trigger | Strip Behaviour |
|---|---|---|
| Coin detected | New coin inserted | Breathing pulse (all LEDs) |
| Progress update | After coin is registered | Fill left to right, red → yellow → green |
The NeoPixel strip plays the role the vending machine display did, making progress visible and rewarding, even when the goal is weeks away.
Stage 6 - The Saving Loop
How It Works:
SmartPiggy follows a simple, repeatable interaction loop, bookended by the parent at the beginning and the child's achievement at the end.
The Interaction Flow:
0. Set the Goal - Before saving begins, the parent sets a savings goal through the companion app. The goal is sent to SmartPiggy via WiFi. The solenoid locks the coin chamber. The journey begins.
1. Wait - The system is idle. The IR sensor is continuously monitoring the coin slot.
2. Detect - A coin is placed in the slot. The IR sensor registers its presence, the beam is broken, the system wakes up.
3. Prompt - The system signals the child to act. A light or sound indicates that a coin is waiting and a choice needs to be made.
4. Identify - The child looks at the coin and recognises its denomination. Active recall, not automation.
5. Decide & Confirm - The child presses the denomination button. This is the moment of commitment.
6. Accept - The servo opens the flap. The coin drops through into the chamber.
7. Acknowledge - NeoPixel lights update. A soft tone plays. The deposit is recognised.
8. Celebrate - At 25%, 50%, 75%, 100% of the goal, a milestone is triggered. Lights flash, special audio plays.
9. Return - System returns to idle. IR sensor resumes monitoring. Ready for the next coin.
10. Goal Achieved! - When the total reaches the goal, a final celebration triggers lights, sound, the full works. The solenoid unlocks. The coin chamber opens. The child retrieves their savings.
Algorithm:
Parent sets goal via app → solenoid locks → IR sensor idle → coin detected? → prompt child → wait for button press → update total → trigger servo → coin accepted → check milestone → acknowledge or celebrate → check if goal reached? → NO → return to idle → YES → final celebration → solenoid unlocks
Flowchart Diagram
Materials
| Qty | Description | Price | Link |
|---|---|---|---|
| XIAO ESP32-C6 | Main controller, WiFi built in | 00.00 $ | link |
| IR sensor module | Coin detection | 00.00 $ | link |
| Tactile push buttons | Denominations | 00.00 $ | link |
| MG90 servo | Coin flap | 00.00 $ | link |
| NeoPixel LEDs | Progress bar | 00.00 $ | link |
| DFPlayer Mini | MP3 playback | 00.00 $ | link |
| Speaker 3W 4Ω | Snout audio | 00.00 $ | link |
| Solenoid 5V | Lock mechanism | 00.00 $ | Mini Push-Pull Solenoid 5V |
| Decoupling capacitors | Power stability | 00.00 $ | link |
| Pull-down resistors | Button inputs | 00.00 $ | link |
| JST connectors | Module connections | 00.00 $ | link |
| Battery | To be decided | 00.00 $ | link |