Portable Dermatoscope

Solution

Our dermatoscope fits right in the hand and is super easy to use. It can be operated via two physical buttons on the device or remotely through a mobile application. Users have the option to select between standard and polarized lighting modes, with adjustable brightness settings for each. This flexibility helps doctors quickly set up the device for different situations, making skin exams more accurate and efficient.

On one hand, our main goal was clear: to modernize the device by upgrading its components to up-to-date ones and develop new embedded firmware. On the other hand, we ran into some tough mechanical limits because the PCB had to fit a very specific size and shape.

We had some tight restrictions on where we could put components, which made the design more complex. The device is super compact, so fitting all required elements into such a small space was no easy task.

Two PCBs

The device has two PCBs: the main one with all the electronics and LEDs, and a separate USB board. They connect via cable due to the device’s layout, with the USB port positioned at the bottom and the main board located at the top.

In the previous dermatoscope model, the main board was designed as a four-layer PCB. With the integration of additional components, the engineering team decided to switch to a six-layer board but kept the same size. The additional layers allowed us to add more routing channels, accommodating the more complex circuitry.

Charging

The dermatoscope’s USB-C charging port now supports a faster 2.1A current in the new model, cutting down charge times significantly. Achieving this required a custom internal interconnect cable between PCBs. It wasn’t easy because the cable had to be thin and flexible to fit inside the small case, handle the higher current, and be feasible for manufacturing at scale.

Controller

The previous dermatoscope model relied on a microcontroller that lacked wireless capabilities and consumed a lot of power. Since one of our main goals was to implement wireless communication, we decided to go with the Nordic nRF52840 plus a Bluetooth antenna. This chipset has performed really well in our past projects — it’s energy-efficient, cost-effective, and fits nicely into compact enclosures.

Battery level indication

This model introduces a new feature: battery charge indication using four LEDs. When fully charged, all four LEDs light up; at 75%, three LEDs are on, and so forth. The client requested that the LEDs don’t simply switch on and off but instead smoothly fade in and out, creating a gradual light transition effect. 

To implement this, we replaced transistor-based circuits with a dedicated LED driver IC. We developed firmware that synchronizes the operation of all four LEDs, ensuring accurate and visually appealing battery status indication.

Access via mobile app

The iOS app was built by the client, and our task was to enable Bluetooth connectivity between the dermatoscope and smartphone. Users can then manage the device straight from the app. A key challenge, however, revolved around the enhanced security requirements for Bluetooth pairing. To initiate device control, users either press and hold a button on the dermatoscope or enter a special PIN code in the app.

Major Issues Resolved

Complex component placement 

The new version of our device packs more features without growing in size, forcing us to tighten up the component placement on the PCB. Adding a wireless antenna chip introduced a whole new set of layout challenges — antennas require generous space and careful positioning. Because the antenna occupies a significant portion of the board, it became tricky to place other elements efficiently. We had to evaluate different antenna designs to find the one that’s least sensitive to placement and design variations.

On top of that, the product’s casing design created restricted areas on the PCB where components couldn’t be placed, so we had to carefully plan around those constraints.

Miniaturized component sizing

To keep the device compact, we had to work with incredibly small parts — not always an easy task.

The first big issue was with the RGBW LED used to show wireless status. The client requested an incredibly small 0.8x0.8 mm LED, with 0.2 mm pads on each of its five pins.

The factory had trouble soldering such a tiny component consistently. As a result, some boards had LEDs working fine, while others didn’t.

The engineer made a design change to the protective layer geometry around the contact pads in the next revision to prevent shorts during soldering. This improvement led to a clear reduction in production rejects.

Our device’s tight form factor created hurdles in selecting the controller. The standard nRF52840 module with integrated antenna was just too large to fit. To solve this, we opted for the bare nRF52840 chip with BGA pads in a compact 6x6 mm package, paired with a custom external antenna and the necessary matching circuitry and filter.

State machine issues

Our device operates in several modes: 

• off (with minimal power consumption), 
• sleep mode where only Bluetooth is active, 
• charging, 
• polarized and non-polarized backlight modes, 
• pairing with a mobile phone.

Switching between these states is triggered by button presses — short or long. Each state has its unique characteristics, and together they form what we call a state machine.

In the initial version provided by the client, some of these state transitions were incorrectly defined. Our engineers carefully reviewed the logic, identified the issues, and proposed a revised state machine that ensures all modes work correctly. The client approved our solution.

The Scope of Work

• Schematic and PCB design

• PCB assembly, testing, and fixing

• Firmware development

Technologies Used

• Altium Designer for schematics and PCB design.

• The core MCU is the Nordic nRF52840 chip with Bluetooth 5.0 LE support.

• Illumination is provided by 21 white LEDs: 15 cross-polarized (XP) and 6 non-polarized (NP), achieving an illuminance of 25 kLux.

• Two tactile push-buttons for control.

• USB-C input, 5V/2.1A, IEC 62368-1 certified.

• Custom firmware is created with C++, VS Code IDE, CMake cross-platform tool, and the GCC compiler.

• Powered by a 1800mAh, 3.7V lithium-ion battery.

Result

Together with our client, we developed an upgraded pocket dermatoscope that stays just as compact and user-friendly as before but now packs in new features — from wireless control to smooth status indicators and rapid charging. These enhancements made the device even more convenient and reliable for dermatologists in their daily workflow.

At present, we’re discussing the possibility of creating a brand-new digital dermatoscope model with two advanced cameras. This device will capture detailed skin images, process them efficiently, and transmit the results to smartphones and expert systems, enabling more precise diagnostics.