Bluetooth LE wearable buttons

[Catalin Anesia]

Hi everyone, A beginner here with an idea for a small project. Project specs: 4 BLE buttons paired to a Android or iOS phone and an app that will listen which button has been pressed and will trigger a app defined action within the app itself. The buttons + board + battery will be mounted on a bracelet configuration.

Where do I start, what do I need to buy and use, what should I read ? any help is welcomed!

This is the project setup in my mind: 4 buttons via BLE board paired to the phone with the app active in background. When a button is pressed a unique ID is sent to the app then the app recognize the button and performs an action. I do not have a problem with the app development but with the electronics that I should buy and use. Thank you all, Catalin Anesia

[Øyvind Karlsen]

Hi Catalin,

I will try to outline roughly what needs to be done, so bear with me if this is not as comprehensive in some parts as you would like(ask if you have any questions!).

First off, what you will need.

• nRF51 Development kit

• nRF51 Dongle(optional, but recommended, makes prototyping a lot easier)

• An IDE, I prefer Keil, but there are many alternatives

• Some physical buttons(You can also use the four buttons that are already on the nRF51 DK)

Once you have all your components lets start prototyping. Here you will need some hands on experience with the kit, and your chosen IDE. I suggest starting with these three tutorials.

• Setting up an example project on the nRF51 DK

• Testing and using a simple BLE application

• BLE Advertising, a beginner's tutorial

Now that you have some basic knowledge about our kit, and BLE we can start prototyping the device. Lets connect the buttons, actually, while prototyping you can use the four buttons that are already on the nRF51 DK, however this is up to you. If you do decide to prototype with custom buttons make sure that you hook them up in a non-floating configuration(this tutorial explains this well), otherwise you might get a lot of erroneous readings.

Next lets configure the buttons to do something, the easiest way of doing this would be to use the material covered by the tutorial on the Board Support Package. There are some more ways to do this, but they are arguably harder(One solution is using GPIOTE from the SDK). Whichever solution you chose I have one imperative recommendation, use interrupts! They are one of the most critical things to make your application energy efficient, which is one of the key requirements in a wearable application like yours.

Now that we have setup the development kit to take interrupts from its buttons we need some way of transmitting this information over BLE. This part I will leave partially unanswered, as you will have a pretty good idea on what to do once you've gotten to this stage. One idea is to transmit your information like you did in the tutorial on Testing and using a simple BLE application.

For the app side development, I can't be of any help, but this would be a logical next step.

Finally when you have a working prototype you will want to design and produce a PCB, this I will also leave to you. For help on designing the PCB, consult the product specification and the nRF51 DK Hardware Files.

Hopefully this answers your question, best regards,

Øyvind

[Catalin Anesia]

Dear Øyvind Karlsen, thank you very much for your detailed answer. It looks like I will have fun and not too much sleep. Definitely your answer got me on the right direction, appreciate that. I will post forward as I will progress ... Any other comments/ideas are welcomed. Best regards, Catalin.