Busy StatusBar: Uncovering mechanical and electrical components

This is a third chapter of our journey building the Busy StatusBar. Previous parts [1],[2].

Busy StatusBar is a portable LED device that beautifully visualizes user's active status and could serve as a Pomodoro timer.

We build it for productivity and creative mind. User can integrate the device into everyday workflow, and show visuals that best communicate active status.

This chapter will cover:

• Design of chassis and plastic mesh.
• Mechanics of controls.
• Mounting on vertical surfaces: screw holes and magnets.
• Electronics: circuit boards, battery, speaker.

Previous chapter was more about exterior design. Today we will dive deeper into design, mechanics and processing of internal parts.

What's inside the device

The central element of the device's layout is the chassis, on which the buttons, two boards, the speaker, and the battery are attached. The assembly with the chassis is placed in the body and closed with the display assembly.

The display assembly includes the following components:

• LED matrix with a resolution of 16x72 pixels;
• A plastic mesh separates pixels and isolates the light emitted by neighboring LEDs;
• A diffusing film ensures consistent light distribution within each cell;
• The tinted front cover creates a uniformly dark surface, concealing the internals of the device.

In high-volume plastic molding production, achieving a thickness of the light-isolating grid's walls below 0.6 mm can be challenging. The distance between the LEDs must be a minimum of 1 mm (a 0.6 mm mesh thickness and 0.2 mm tolerance to accommodate any errors around the LED). Knowing the size of the LEDs and determining the appropriate spacing between them, we were able to determine the final dimensions of the matrix and the device.

Mechanics of the controls

The device incorporates tactile buttons. To ensure uniform actuation of the large button, we have employed a principle inspired by the "spacebar" key on a keyboard: using a metal stabilizer, the button press is synchronized from all sides.

Our large button worked, although we encountered an issue caused by the friction of the components. The 3D-printed parts had a rough surface, but a brief filing session resolved the issue.

In addition to the buttons, the device also features an encoder wheel that requires pressing. We have incorporated a similar concept found in mouse wheels. On one side, the shaft is connected to the encoder, while on the other side, it rests on a micro switch that is triggered when the wheel is pressed.

Mounting on vertical surfaces

We added holes under the back cover to make it easier to hang the device on screws. This feature enables mounting the device on vertical surfaces, providing a stable and rigid installation.

This solution works well, but comes with a few considerations:

• You need to remove the back cover for access to the ports. Given that the cover is secured with clasps, there's a slight risk of damage, which could prevent the cover from fitting back in place;
• The OLED display is getting exposed, which could potentially lead to its damage;
• The precision required to align the ports with the screws can sometimes lead to minor cosmetic damage to the device's finish.

Our design engineers recommend eliminating the screw holes and preventing users from disassembling the device, an approach that can minimize potential damage. Alternatively, we could design through-holes in the back cover which would require external plugs. This option would impact the design integrity and require an additional component, consequently increasing the cost.

I consider incorporating magnets into the back of the device, enabling it to attach to a metallic surface. To make the magnet useful, we consider including a slim metal plate with with double-sided tape in the package. User would stick the plate onto any surface: door, monitor, or wall, and then attach the device to the plate. What do you think would be the better solution – the magnetic one or the one with holes?

For B2B segment, we might offer a version without the rear display and with open mounting holes in the body. Leave a comment if you're interested that.

Electronics: circuit boards, battery, speaker

The electronic hardware of the device includes a battery, a speaker, and three boards:

• The board with the LED matrix (display)
• The board with an ESP 32 processor, control interfaces, and a USB-C port
• The board with an OLED display and encoder

The boards interconnect via FPC (Flexible Printed Circuit) cables. We're considering a more rigid connection through spring-loaded contacts.

The design allows for a battery sized 17 x 120 x 20 mm. A lithium-ion battery of this size would have an estimated capacity of 3200 mAh. We measured the LED matrix's consumption in a busy state with a timer, yielding around 135 mA per hour.

Accounting for the ESP32 and OLED display's consumption, we estimate a total power draw of 350 mA per hour, allowing the device to display status for approximately 9 hours without recharging.

We will be ordering custom-sized batteries for the final device.

We positioned the speaker on the side of the device and incorporated four small openings in the case to enhance sound clarity. Our tests revealed that there was no noticeable difference in loudness when using either 8 Ohm or 4 Ohm speakers.

Due to the limited number of pins available to connect the ESP32 microcontroller, we decided not to include an external DAC (Digital-to-Analog Converter). Instead, we used a pulse width modulation (PWM) module built into the microcontroller and installed an external low-pass filter. Following the filter, we installed a D-class digital audio amplifier.

While the sound produced is sufficiently loud, we did encounter some polyphony. We avoided using a buzzer so Busy StatusBar could have pleasant audio feedback.

RS-485 communication

The device is equipped with an RS-485 commonly used in industrial networks. We've allocated four pins for this: twisted pair, ground, and power. We're considering its usage in the B2B segment for network panel connection or for creating an array from multiple devices. We haven't decided on a protocol yet, but we're planning to adapt according to market demands.

This is not the entire progress we've made over the last 6 months. The following articles will cover:

1. The initial lines of code we wrote for the device.
2. How we assembled and tested the first prototypes for Pomodoro technique.

How to buy?

We have exciting plans to bring the device to market through a crowdfunding campaign on Kickstarter, which we will launch later this summer. We hope to send the finished devices six months after the end of the fundraising.

Want to be updated on our progress building the device? Check our TikTok, Instagram and Twitter for new use cases, images and animations.