Cardio Wristband: A Smart Heart Rate Sensor
Cardio Wristband: A Smart Heart Rate Sensor
Cardio Wristband is an amazingly small heart rate sensor. It broadcasts to your smart phone or tablet.
Cardio Wristband is an amazingly small heart rate sensor. It broadcasts to your smart phone or tablet. Read more
About this project
An Amazing Heart Rate Sensor
Cardio Wristband has been engineered from the ground up to be what a heart rate sensor should be. It is small, accurate, and best of all does not require a strap like traditional heart rate sensors.
Cardio Wristband senses your heart rate and broadcasts it wirelessly to your smartphone or tablet. It uses the Bluetooth Smart Heart Rate protocol. It works with a large variety of hardware devices and apps.
How It Works
Cardio Wristband works similarly to heart rate monitors found in hospitals. Light shines through the wrist. Blood flow causes the amount of light to change with each heart beat. The changes are measured to give the current heart rate.
Who Is It For
Cardio Wristband is a great alternative to traditional Bluetooth enabled chest straps. It's much smaller, there is no need to wet it, and it is easy to put on. People who currently listen to music on their phones or iPods while working out will enjoy seeing their heart rate too. Some apps will even voice the heart rate to you and record the values while you're working out.
In early 2012 I began exercising with a heart rate monitor. I wondered if one could be designed to work with my smart phone. In July of 2012 I began designing the circuit board for the Cardio Wristband full time. I began first by choosing a Bluetooth Low Energy chip from Texas Instruments and ordering their development kit.
Each prototype circuit board was custom made and went through several revisions. The first prototype was made large and eventually it evolved into a prototype that was small enough to fit into a wristband.
The bulk of the work has been to get a clean heart rate signal. The work has paid off and now there is a working prototype that reads the heart rate quickly and accurately. It updates even when you are moving your arm around during exercise.
The prototype plastic was made with a Solidoodle 3D printer. A standard watch band can be fitted to give a customized fit or look. It comes fitted with a black band. It uses a rechargeable LiPo battery that can be charged with a micro usb cable. It has a small on/reset button. The wristband connects automatically to the phone or tablet once it is turned on. It turns off automatically when it has been disconnected from a device for five minutes.
Supported Devices and Software
iPhone 4S, 5 and newer
iPad(3) and newer
iPod Touch (5th generation)
Android support for this standard is new and requires an Android device with Bluetooth Smart hardware that is running OS 4.3 or higher.
The Nexus 4, Nexus 7, and HTC ONE have been tested.
The Samsung Galaxy S3 and S4 should be updated to 4.3 by the end of October. The Sprint EVO 4G LTE will be updated by the end of the year.
Apps that support the Bluetooth Smart Heart Rate protocol will work. Running apps such as RunKeeper are a great choice. Simply search for "Bluetooth Heart Rate" in either the Apple App store or the Google Play Android store for a third party app.
Below is a tentative schedule for production of the Cardio Wristband.
October - November:
I have begun adding a lcd screen based on requests from members. Please see the updates for more details. It is a high quality memory lcd from Sharp. More software must be written to create the drawings and user interface for the screen.
Funds from the campaign arrive.
The electronic components will be ordered. This includes the IC's, resistors, capacitors, crystals, and other parts that are placed on the PCB (Printed Circuit Board).
Small revisions to the PCB will be made to make it easy to manufacture. This step is called DFM (Design for Manufacturability).
Plastic molds will be made for the center plastic that holds the battery and electronics. CAD models will be used for this step. A basic CAD model is already used with the 3D printer for the prototype. Standard watch bands will be ordered to attach to this piece to speed up production.
Extensive field testing of the product will be made. Any necessary plastic or design revisions will be made based on testing results.
The plastics will then be injection molded. The final product will look very similar to the prototype but may differ slightly cosmetically.
January through February:
Wireless certification will begin. The product will need FCC and Bluetooth certification. A third party lab will perform the certifications.
The bare circuit boards will be manufactured by Sunstone Circuits in Oregon. They make high quality boards and were used for the prototypes.
PCB assembly will begin with a contract manufacturer within Minnesota. This is the step where the electronic components are attached to the bare circuit boards. This is mostly automated so the boards will be assembled quickly.
March through April:
Final assembly of the wristband will occur. This involves inserting the electronics into the plastic module and attaching the watch bands. Then the wristbands have to be tested, boxed, and shipped to backers.
Cardio Wristband LLC is my company. My professional experience is with mobile software development and embedded electronics. This project has been a great fusion of my passions and a lot of fun.
Risks and challenges
There is a minor risk that the wristband will need to be revised during the wireless certification process and retested if it does not pass certification the first time. The circuit board layout and performance will be reviewed by another lab prior to FCC testing to increase the chances of passing the first time.
If production of the plastics or pcb assembly is slow for some reason that could cause a delay. This should not happen but it is a possibility. The boards are going to be assembled in Minnesota so that local and onsite communication can speed up production.
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