Android Doorbell Notifier

Breadboarded circuit to detect when doorbell rings

It’s always unfortunate to find a FedEx tag on your door saying you missed a delivery; especially when you were home the whole time. After having this problem a few times [Lee] decided to rig up a doorbell notifier for his Android phone.

[Lee]‘s doorbell uses a 10 VAC supply to ring a chime. To reduce modifications to the doorbell, he added an integrated rectifier and a PNP transistor. The rectifier drives the transistor when the bell rings, and pulls a line to ground.

An old Netgear router running OpenWRT senses this on a GPIO pin. Hotplugd is used to run a script when the button push is detected.

The software is discussed in a separate post. The router runs a simple UDP server written in C. The phone polls this server periodically using SL4A: a Python scripting layer for the Android platform. To put it all together, hotplugd sends a UNIX signal to the UDP server when the doorbell is pushed. Once the phone polls the server a notification will appear, and [Lee] can pick up his package without delay.

Arduino Garage Door Opener is Security Minded

Arduino garage door opener

Do it yourself garage door openers must be all the rage nowadays. We just got word of another take on this popular idea. [Giles] was commissioned by his friend to find a way to control the friend’s garage door using a smart phone. The request was understandable, considering the costly garage door remote and the fact that the buttons on the expensive remote tended to fail after a while. The inspiration for this project came from some YouTube videos of other similar projects. Those projects all paired an Arduino with a Bluetooth headset in order to control the door from a mobile phone. [Giles] understood that while this would get the job done, it wouldn’t be very secure. Bluetooth headsets typically connect to mobile phones using a four digit PIN. Many of them have known default PINs and even if the default is changed, it wouldn’t take very long to guess a four digit PIN. [Giles] knew he had to find a more secure way.

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Simplest of SL4A microbridge examples

We’re familiar with the daunting task of sifting through mountains of code in hopes you can learn how something works. So when a simple example like this SL4A LED toggle comes along we’re thankful for the trimmed fat. If you’re looking to use an Android device to control your Arduino hardware this will be huge shove in the right direction.

The microbridge is used to get the Arduino talking with the Android phone. It involves a USB host shield that lets you connect the two devices via a USB cable. With the USB debugging enabled on the phone, you can use Scripting Layer for Android as a user interface. In this case, a set of Python scripts builds the button and readout seen on the screen above. They also handle sending and receiving commands based on user input. This means you don’t really need to know anything about Android development. We think it would be a great way to get your project through the development stages, and you could learn to write a traditional App later on.

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Adding speech control to an old robotic arm

[Joris Laurenssen] has been hanging onto this robotic arm for about twenty years. His most recent project uses some familiar tools to add voice control for each of the arm’s joints.

The arm has its own controller which connects via a DB-25 port. [Joris'] first task was to figure out what type of commands are being sent through the connection. He did some testing to establish the levels of the signals, then hooked up his Arduino and had it read out the values coming through the standard parallel connection. This let him quickly establish the simple ASCII character syntax used to command movement from the device. There’s only eight command sets, and it didn’t take much work to whip up a sketch that can now drive the device.

The second portion of the project is to use voice commands to push these parallel signals to the arm. Instead of reinventing the wheel he decided to use the speech recognition feature of his Android phone. He used Scripting Layer for Android (SL4A) and a Python script to interpret commands, push them to his computer via Telnet, and finally drive the arm. We’ve embedded the video demo after the break. He gives the commands in Dutch but he overlaid comments in English so you can tell what’s going on.

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