A $20 Heart Rate Module For Health-Tech Projects

Heart rate monitoring is a common procedure for most of health related projects. Therefore, producing sensors modules and circuit boards for such tasks will facilitate and push forward the development of new health-tech projects.

Maxim Integrated, an analog and mixed-signal integrated circuits manufacturer, has developed a new module for measuring heart rate and pulse oximetry. It’s called “MAXREFDES117#”, derived from Maxim Reference Design, and it is a small board which is compatible with Arduino and Mbed boards, enabling a wide range of possibilities for developers.


MAXREFDES117# can be powered by 2 to 5.5 volts. It is a photoplethysmography (PPG)-based system that uses optical method for detecting heart rate and SpO2. It consists of three main parts:

1. MAX30102, a high sensitivity heart rate and pulse oximetry sensor. It is used with integrated red and IR LEDs for heart rate and pulse oximetry monitoring.

2. MAX1921, a low-power step-down digital-to-digital converter. It generates 1.8 V from input to supply the sensor.

3. MAX14595, a high speed logic-level translator. It works as an interface between the sensor and the connected developing board.

MAXREFDES117 Block Diagram
MAXREFDES117 Block Diagram

The board size is only 0.5” x 0.5” (12.7mm x 12.7mm) and has low power consumption that make it suitable for wearable applications. Thus, it can be placed on a finger, an earlobe, or other fleshy extremity.

MAXREFDES117# uses open-source heart-rate and SpO2 algorithm in its firmware. It also can be used with any controller having I2C interface. But the available firmware had been tested only on 6 different development boards, three of them are Arduinos (Adafruit Flora, Lilypad USB, and Arduino UNO), and the others are mbed boards (Maxim Integrated MAX32600MBED#, Freescale FRDM-K64F, and Freescale FRDM-KL25Z).

The MAXREFDES117# Firmware Flowchart
The MAXREFDES117# Firmware Flowchart

Accuracy of data collected by MAXREFDES117# depends on the used platform. According to the results with tested boards, Arduino boards give less accuracy than mbed ones because of theirs smaller SRAM size.

MAXREFDES117# is available for $20, it can be ordered online through the website.
More detailed information and quick start guide are presented here. In addition, all of the source files including schematic, PCB, BOM, and firmware are open and can be reached at the official product page.

An open-source IoT power meter

The first step toward finding ways to reduce home electricity usage begins with installing an energy monitoring system. These days you can find an electric meter in every residence, but it is likely that you would find it installed in a location that is more convenient to access for a utility person and not for you, the homeowner. This DIY Internet-of-Things enabled power meter is what you would need for an easy access to the real-time electricity usage data right on your computer screen at your desk.

IoT Power meter
IoT Power meter

This IoT power meter (IPM) is designed by Solenoid and it works in conjunction with a regular watt meter that consists of a flashing LED as a watt-hour usage indicator. The IPM senses the blinks of the LED using a light-dependent resistor (LDR), counts those pulses, saves the values to an SD card, and later uploaded to a cloud service, such as Google spreadsheet, for remote access using internet. Another advantage of IPM over the regular power meter is it extrapolates the measured data samples for improved resolution and estimation of energy usage.

The heart of this project is the WiFi-enabled ESP8266 microcontroller, which is coupled to an SD card and a 0.96” OLED screen. The SD card is used for storing the energy usage data as well as the HTML web pages that are served by ESP8266 on a client’s request. The network credentials required by ESP8266 to connect to a WiFi router are hardcoded into the firmware. The OLED serves as a local display for showing the current time and date, local IP address of the ESP8266 device, watt-hour usage for the day, etc. For accuracy, the ESP8266 synchronizes its local time with an NTP server.

IPM prototyping on a breadboard
IPM prototyping on a breadboard

The IPM is an open-source project and costs about $20 to build. The BOM and detail documentation can be found here.

Wireless biosensor platform for medical disposables


STMicroelectronics and HMicro have announced a single-chip product for disposable, clinical-grade wearable patches and biosensors, to replace wires for vital-sign monitors and electrocardiograms. The IC technology developed by HMicro and ST also targets other high-volume clinical and industrial-IoT applications. By Graham Prophet@ edn.com:

Hmicro is a wireless solutions developer working in wireless peripherals and complex biosensor applications. With STMicroelectronics the two companies have launched their cooperation to create the first single-chip solution for clinical-grade, single-use disposable smart patches and biosensors. The product, HC1100, targets the 5 billion wired wearable sensors, such as those for vital-sign monitors and electrocardiogram leads, utilized annually.

Wireless biosensor platform for medical disposables – [Link]

FFTs and oscilloscopes: A practical guide


Arthur Pini @ edn.com published a guide on how to use FFT found in most modern oscilloscopes.

The FFT (Fast Fourier Transform) first appeared when microprocessors entered commercial design in the 1970s. Today almost every oscilloscope from high-priced laboratory models to the lowest-priced hobby models offer FFT analysis. The FFT is a powerful tool, but using it effectively requires some study. I’ll show you how to set up and use the FFT effectively. We’ll skip the technical description of the FFT, because its already implemented in the instruments. Instead I’ll focus on the practical aspect of using this great tool.

FFTs and oscilloscopes: A practical guide – [Link]

Arduino Touch Screen Music Player and Alarm Clock Project


Dejan Nedelkovski build an Arduino-powered MP3 Music Player plus Alarm Clock. The player has a 3.2″ TFT display and the home screen displays time, date and temperature along with touch control buttons.

In this project I will show you how you can make an Arduino Touch Screen MP3 Music Player and Alarm Clock. You can watch the following video or read the written tutorial below.

Arduino Touch Screen Music Player and Alarm Clock Project – [Link]

Lightweight Body Heat – Electricity Converter

Powering wearable technologies using thermoelectric generators (TEGs) is becoming more efficient. An undergraduate student in North Carolina University, Haywood Hunter, is producing a lightweight and an efficient wearable thermoelectric generator. It generates electricity by making use of the temperature differential between the body and the ambient air.This converter produces 20 times more electricity than other technologies (20 µwatts) and it doesn’t use any heat sink, making it lighter and much more comfortable.

Study co-lead Haywood Hunter, shows off the TEG-embedded T-shirt at work.
Study co-lead Haywood Hunter, shows off the TEG-embedded T-shirt at work.

The design begins with a layer of thermally conductive material that rests on the skin and spreads out the heat. The conductive material is topped with a polymer layer that prevents the heat from dissipating through to the outside air. This forces the body heat to pass through a centrally-located TEG that is one cm2. Heat that is not converted into electricity passes through the TEG into an outer layer of thermally conductive material, which rapidly dissipates. The entire system is only 2 millimeters, and flexible. Some limitations to size can be solved by choosing right power settings for different sizes.

Even though the wrist is the best place to use heat-electricity converters because the skin temperature is higher, the irregular contour of the wrist limits the surface area of contact between the TEG band and the skin. To solve this issue, it was recognized that the upper arm was the optimal location for heat harvesting. Meanwhile, another experiment showed that wearing the band on the chest limited air flow and heat dissipation, since the chest is normally covered by a shirt.The researchers found that the T-shirt TEGs were still capable of generating 6 µW/cm2 – or as much as 16 µW/cm2 if a person is running. It was realized then that T-shirts are just not as efficient as the upper arm bands.

TEG-embedded T-shirt (left) and TEG armband (right).
TEG-embedded T-shirt (left) and TEG armband (right).

The work was funded by National Science Foundation (NSF) and the research was done in the Nanosystems Engineering Research Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST) at North Carolina State. This center’s mission is to create wearable, self-powered, health and environmental monitoring systems, such as devices that track heart health or monitor physical and environmental variables to predict and prevent asthma attacks.

Further details can be reached at the university website and the project’s paper.

Via: ScienceDaily

LTM2889 – Isolated CAN FD µModule Transceiver and Power


The LTM2889 is a fully ISO 11898-2 compliant CAN (controller area network) μModule transceiver and isolator that guards against large ground-to-ground differentials and common mode transients in 3.3V or 5V applications. In practical CAN systems, ground potentials vary widely from node to node, often exceeding the tolerable range, which can result in an interruption of communications or destruction of a transceiver. The LTM2889 separates grounds by isolating the CAN transceiver using internal inductive isolation. It implements multiple levels of protection to significantly improve system reliability, including 2,500VRMS of galvanic isolation, ±60V bus voltage fault tolerance, greater than 30kV/μs common mode transient immunity, and ±25kV HBM ESD protection. The LTM2889 requires no external components, ensuring a complete and robust μModule solution for isolated serial data communications.

LTM2889 – Isolated CAN FD µModule Transceiver and Power – [Link]

RGBW LED Controller v3.1


Jeremy @ thecustomgeek.com updated his RGB LED controller with a bunch of improvements.

The new RGBW LED Controller is here! The video above shows some of the things it can do, but here is a list of improvements:

IRLB8721PBF MOSFET’s – More power!

Double sided and thicker board traces

RGBW LED Controller v3.1 – [Link]

Tibbo Project System-based Aircon Controller Application


The app allows you to manage traditional air conditioners that are controlled through infrared remotes. Designed for the office environment, the app relies on the ambient brightness (measured by Tibbit #28) to determine whether the aircon should be running or not. In the office setting, no lights = no people = no need for the aircon to work.

Air conditioning is a consumptive business while air conditioners are big-ticket to run. In general, AC systems, older ones, in particular, do not have any real temperature feedback. You set the temperature on your remote, but alas, it has absolutely nothing to do with the actual temperature in the room. Even when it gets colder outsides, many aircons keep blasting cold air into your space. As a result, you have to constantly readjust the temperature as needed for optimal comfort throughout the day.  (more…)

8 Channel RS485 Relay Board


This project helps you control 8 relays using RS485 link with the help of a PC. This kit can effectively convert  a standard PC to a powerful   PLC ( programmable logic controller ). At the PC end , you will need to use our RS232 to RS485 Interface – C020 or any other suitable RS232 to RS485 Converter.

The project can offer a low-cost serial relay contact interface, easy to use with Visual Basic, Basic, C, Labview, Testpoint, or other high level languages that allow access to a serial port.

You can simply use the accompanying software provided with this project or issue control commands using any popular Terminal Port software available on the net.

The Serial port on the computer should be configured to 2400 baud – 8 bit words – 1 stop bit – no parity

8 Channel RS485 Relay Board – [Link]