benlhy/wireless_measurements

A simple, compact wireless tool to measure low power circuits

Introduction

The Simple Wireless Measurement (SWM) board is just that - it is a simple board designed to do wireless measurements for remote embedded circuits. It is capable of measuring current and voltage and transmitting it over Bluetooth.

You can retrieve the data with Python, NRF Connect App, or the Flutter app designed to display this data.

Related Repos

• Software - Coming soon!
• Android/iOS - Coming soon!

Contents

1. Mini - Contains the KiCAD files required for the mini board version
2. Stick - Contains the KiCAD files required for the standard board version
3. Arduino - Contains the KiCAD files required for the arduino implementation.

How to use

1. Open the project in KiCAD. Export the gerber files and send it to the manufacturer of your choice. Some I've used before are JLCPCB and PCBway.
2. Assemble the board
3. Refer to the software repo to flash the software for the board you are using
4. Test the board using nRF Connect or the Python script or the Flutter App

Technology

The SWM board uses an EFM8LB12 microcontroller from Silabs to do the analog measurements. The EFM8 is capable of 14-bit ADC measurements with multiple inputs.

The SWM board uses the JDY-08 Bluetooth module because it provides a simple and transparent way to communicate readings over BLE: just connect and send the data over UART. It is also a very low-cost module (< $4). It can also be replaced with the JDY-23 which provides lower power draw, UART baud rate of 9600, and a lower cost of < $1 per module.

It is powered by the MCP16415 boost module which can take input ranges from 0.8V to 5.5V, which means that it can be powered by anything from a single AA rechargable to a 5V input from another board.

The total cost of the board comes up to roughly $15, which makes it cheap enough to throw permanently into a system to do wireless reporting of voltage and current. The board size is also small - about the size of two postage stamps placed side by side, which allows it to be embedded in other applications.

Use case	Description
Drones	Measure the power draw of electronics on your drone over time
Robotics	Keep an eye on motors and batteries
IoT	Monitor battries remotely
Distributed systems	Monitor various test points in the system simultaneously to get a holistic picture of what is going on
Rocketry	Monitor your wireless systems as you mount the rocket. Never wonder again if your system is dead.

Specs

Measured Current draw	Supplied Voltage	Status	Version
48 mA	1.2V	Fully On	JDY-08
15 mA	3.3V	Fully On	JDY-08
35 mA	1.2V	Fully On, Connected	JDY-23
31 mA	1.2V	Fully On, Broadcasting	JDY-23
9 mA	3.3V	Fully On, Connected	JDY-23
8 mA	3.3V	Fully On, Broadcasting	JDY-23

Arduino Version

The Arduino Version is a simplified version of the full board but can be programmed directly in Arduino. It has a lower ADC resolution and a lower UART baud rate because it is using Software Serial.