Custom IoT LED Pendant Necklace Design & Development

A key player in premium jewelry desired a stylish new LED pendant necklace aimed at elegant customers. The goal was to create an LED pendant necklace that had no externally visible electronics, had the appearance of high-quality jewelry, produced soft and warm ambient lighting, and could be comfortably worn.

The solution would involve using miniaturized electronic components, materials science, and industrial design principles.

Aesthetic Constraints

• The electronics must be completely invisible to the end user.
• There should be no visible plastic, wires or seams on the final product.
• The clasp will be designed to look like high-quality jewelry and not a battery case.

Size Constraints

• The size specifications for the pendant were 8-12mm.
• The CR2032 batteries must be integrated into the clasp.
• Ultra thin-conductors must connect each end of the chain to the pendant.

Power Efficiency

• Effective battery life of the product must be between 8-12 hours once it has been activated.
• The size of the battery to be integrated in the clasp of the product is designed for 220mAh.

Light Quality

• The quality of the light produced by the pendant must have a soft glow because harsh LED point light effects are not acceptable for premium products.
• The resulting illumination produced by the pendant must look diffused to enhance the overall premium feel.

Core Components

We created an ultra-low power LED circuit with the following characteristics:

• Directly powered from CR2032 battery
• No microcontroller (MCU) in order to reduce size and cost of circuit
• Optimized for glow effect rather than brightness

Optimized Current of LED

The target current of the LED is between 2 mA and 5 mA, so that:

• There is a soft (.05 lux) glow from the LED
• The battery will last longer
• There is very low heat generated by the LED.

Visualization of Core Circuit

I=V−VfRI = \frac{V - V_f}{R}I=RV−Vf

I = V − V_f R

Where:

• V=3VV = 3VV=3V (battery)
• Vf≈2.0VV_f ≈ 2.0VVf​≈2.0V (warm LED)
• R chosen to limit current to ~3 mA

Battery life estimation:

t=CapacityCurrentt = \frac{Capacity}{Current}t=CurrentCapacity

t = Capacity Current

• Capacity ≈ 220 mAh
• Current ≈ 3 mA
• Estimated runtime: ~70 hours (theoretical)
• Practical usable glow: 8–12 hours (stable brightness zone)

We intentionally under-drive the LED to match luxury product expectations.

6.1 Material Options

• Gold-Plated Brass
• Sterling Silver

6.2 Internal cavity

• Light source: LED
• Diffused light through: Frosted resin core OR Micro laser-cut apertures

6.3 Light Diffusion Methods

• Epoxy resin diffuser
• Sanded inner surface
• Micro perforated designs

6.4 Chain Conductor Design

Two approaches tested:

Option A: Hidden Wire

• Ultra-thin enamel copper wire (36–40 AWG)
• Routed along chain links
• Coated for durability

Option B: Conductive Chain (Advanced)

• Chain itself acts as conductor
• Requires insulation segmentation
• More complex but cleaner design

Final choice: Hybrid approach (wire + chain integration)

6.5 Clasp Battery Module

Custom clasp housing:

• CNC machined metal
• Snap-fit battery holder

Switch options:

• Micro slide switch (hidden)
• Magnetic activation (premium option)

Phase I: Breadboard Testing

• LED brightness assays
• Current improvement
• Diffusion tests

Phase II: Reducing Size

• Micro printed circuit board design
• LED packaging
• Wiring experiment phase

Phase III: Final Prototype

• Full necklace completed
• Final assembly (clasp + battery)
• Real life testing of the product

Recommended Production Approach

Electronics

• PCB: Shenzhen-based FPC manufacturers
• Assembly: SMT micro assembly vendors

Jewelry

• Casting: Lost-wax casting (China / Mexico)
• Finishing: Electroplating, Polishing

Assembly

• Semi-manual assembly for first 1,000 units

• FCC: No significant (Low-Power Handheld PAS)
• CE: Suited for Federal Standard/Safety
• RoHS: Necessary Per Electronics
• Limited RF: Defines Compliance

Leveraged public-domain LED jewelry concepts

Avoided:

• Smart Activation Process
• Sensor-based triggers (optional future feature)

Where Innovated (focus on):

• Aesthetic concealment for the electronics' hardware
• The mechanical refinement

We've Created:

• An Operational Prototype
• Jewelry Style Design
• 10 Hour Glow
• A Scalable Manufacturing Plan

The Product Achieved:

• An Invisible Integration of Electronics within Jewelry
• Luxurious Visual Appeal
• Reliable & Comfortable Wearable Performance

• Engineering enhances the design vision, rather than detracting from it
• Extreme miniaturization is not at the expense of complexity
• Costs are proportional to overall product feel
• Designed to be mass produced

• A magnetic auto ON/OFF clasp
• Lights that turn on with light sensor activation
• A rechargeable version (i.e., Li-Po + wireless charging)
• A multi-color LED product option