Designing the world’s tiniest WiFi sensor boards

One of the tiniest ESP32 based boards is named PicoClick and measures a mere 10.5mm by 18mm! Although it only features only a push button as an input with no other sensor, it uses a USB C interface for both power and programming. Neat. But could we do better?

One of our tiniest boards (non-wireless) yet is the SwitchBee MagSense which is a digital, magnet activated on/off switch for 12V LED strips. It can support switching upto 1.5A LEDs directly. The size of that board is just 7mm x 11mm!

SwitchBee MagSense PCB

The size was selected deliberately such that a standard 10mm drill-hole/ channel could be used on a wardrobe/ cabinet wall to mount the end-device. Hundreds of our SwitchBee MagSense units are now powering LED cabinet lights. There seems to be some interest for this product in the market, especially as a designed and made in India alternative.

We soon realized that we might need to make this switch smarter by adding more sensor options and optionally even a wifi controller! There was also another project where we were developing a tiny version of our TempBee temperature sensors so that they could pretty much be stuck on any surface and would not take much space.

That led us to the development of two boards, both of which have the option of adding WiFi control. One of them features a LiPo battery charger and a micro USB port for power (for USB/ battery powered use cases) and the other uses an innovative wire-to-board connector and can be used as an advanced version of the MagSwitch product (for 12/ 24V line powered products).

The size of MultiBee no-battery board is just 8mm x 30.5mm of which about 7mm is just occupied by a zero-tool plug in wire-to-board connector.

MultiBee with LiPo charging circuit board on the other hand measures 8mm x 37.5mm (that includes the micro USB connector and a JST 2PH LiPo connector on the other side!)

To get a perspective on how tiny the board is, have a look at the size of a typical micro USB cable connector, the red rectangle is approximately the size of our board:

8mm x 30mm

What can these tiny boards do? Glad you asked. The following are the features built-in.

  1. ESP8285 with 2MB flash, 160Mhz
    • This enables 2.4 Ghz WiFi/ ESP-NOW on board!
  2. Built-in chip antenna optimized for size.
    • (option for mounting a uFL/ IPEX off board antenna for better RF also present)
  3. Infra-red transmitter receiver pair for proximity detection
  4. 1 x Capacitive touch input for touch switch detection
  5. Unipolar hall-effect sensor switch for magnetic switch applications
  6. 3-axis ultra-low power I2C accelerometer/ motion-sensor with 1x interrupt pin
  7. I2C pin pads exposed for connecting more I2C devices if required
  8. UART, GPIO0, RST pins exposed for programming and Serial
  9. Supports deep-sleep and wake up on GPIO interrupts from various sensors
  10. ESD protection on input power pins
  11. One LED for output on GPIO2
  12. Supports OTA firmware updates (requires WiFi connection)
  13. Reverse input voltage protection
    • using MOSFET on non battery version,
    • using a low-dropout diode for USB version

Features specific to the LiPo battery powered version:

  1. Low power, high accuracy (+- 0.5C) I2C temperature sensor
  2. 200mA LiPo charger and with active load support
  3. One digital GPIO pin exposed for any future functionality
  4. Micro USB 5V port for power/ battery charging or USB powered applications. Charging/ charge complete LEDs
  5. 2 PIN JST PH connector for LiPo battery charging (can be de-soldered for saving almost 3mm height, but then the battery terminals will have to be soldered in)

Features specific to the non battery version

  1. Supports a wide input voltage range 5V to 26V DC (12V DC recommended)
  2. Integrated 2.5A power switch to switch loads/ PWM directly from GPIO

While available by default, WiFi functionality itself is optional on these boards. There might be custom use-cases where the board is used simply as a low-power and low-cost microcontroller.

Some of these use cases include:

  • Touch toggled LED strips for cabinet/ wardrobe lighting
  • Motion activated alarms/ LED lighting
  • Infra-red or Magnet based LED on/ off controllers for LED lighting activated on door/ drawer opening/ closing
  • Support advance modes like dimming/ instant on/off purely through software

Some WiFi enabled use cases include:

  • Temperature sensing and logging for rooms/ HVACs/ freezers/ vaccine boxes
  • Tiny remote control switches for other Google Home/ Alexa controlled smart devices
  • Smart door/ window open/ close alarms
  • Fall detection
  • Embedded low-power vibration/ motion/ acceleration detection in sports equipment/ industrial machinery
  • Theft alarms
  • Active device tags/ beacons

What stage are we in now (as in January 2022)?

We have designed and verified the circuit design, availability of components (had to go through multiple iterations just for this!)

The design has been sent to our manufacturing partner for test batch assembly. We expect to get the test batch by mid February 2022.

Risk factors

  • Component shortages force us for a redesign
    • we can turn-around within one day with alternatives
  • The RF performance may not be up to the mark due to the ceramic antenna on board + enclosure interference at this scale
    • there is a provision to use the uFL/ IPEX connector for an alternative antenna if required
  • There may be design/ PCB/ assembly defects
    • should be checked and fixed at the end of the first test cycle run
  • Requires a custom programming jig or wires soldered to tiny pads on board for burning the initial firmware
    • We plan to put together a programming PCB jig with Pogo pins
  • We may not reach the requisite MoQ multiple for getting cost reduction from our component distributors/ assembly partners

Interested in this project?

Since we realize that we cannot possibly build all the use-cases on our own, we will solicit your help in developing some of them! If you would like to embed them into your product, we could add up our first production run numbers to get a lower cost per unit for the components and assembly!

There are a few ways in which you could participate

We would like to gauge the interest for a crowd-sourced development of the board/ use-cases. As long as you can commit to a certain minimum order quantity, we are game to explore all options! Some of the options are:

  • You define the functionality, but let us handle the hardware, firmware and online cloud platform with API/ web-hook integration to any of your existing front-end or apps (or even use our SenseSight™ dashboard!)
  • We provide and license the hardware, you program and use it as you require. Optionally you can also subscribe to our online dashboard
  • You wish to embed this into your existing smart product or solution
  • You wish to use it for some of the pre determined use-cases that we have mentioned above

In any case, please fill-up the form below, we would love to discuss the opportunity with you:

    USB+LiPo powered12V+Non-LiPo powered

    magnetic proximity switchinfra-red proximity switchmotion activated switchtemperature loggingtouch-activated switchID tag/ beaconfall/ motion detectionother

    * = required inputs

    In case of any other inputs/ feedback, please do write to us at We’d love to hear from you.

    By adminBee


    Leave a comment

    Your email address will not be published. Required fields are marked *