Resetting Waspmote Plug & Sense! with an external magnet

Waspmote Plug & Sense! can be reset with an external magnet, with no contact. If one node stops working or if a defective behavior is detected, it would be costly to uninstall the node to bring it back to laboratory. This feature allows the network manager to reset the node in a quick and easy way.

The hardware consists of a reed switch connected to the Waspmote reset line. When the user gets the magnet close to the reed-switch, the reset is activated. When the user moves the magnet away, the reset line is released (the external LED will blink) and Waspmote executes the bootloader first and then, the setup function. After the setup, it will continue with the loop function. Next pictures show the right way to reset the node using an external magnet, first moving it closer, and then moving it away.

Figure: Moving the magnet closer to the node
Figure: Moving the magnet away from the node

The magnet is made of neodymium. It is a special, high-power magnet. We only advise to use the magnet Libelium provides. The user must be careful because the magnet is so powerful that it can get stuck to metal objects. Besides, the magnet must be kept away from electronic devices like PCs, batteries, etc, since they could be damaged or information could be deleted.

It is not mandatory, but highly recommended to consider this feature when designing the project. Every Plug & Sense! node comes with the hardware to allow the contacless reset, but the magnet is optional, an accessory. It is highly recommended to purchase one magnet (one unit is enough for many nodes). The user should design the software in a way the node can be reset if things go wrong. Remember that laboratory tests are always needed to validate the feature before your final deployment.

When the node is already deployed in the field, and for instance it is installed in a traffic light, this feature can be used to reset the node easily, as it is shown in the diagram below, where a technician uses a pole with the magnet attached in one side.

Figure: Resetting a Plug & Sense! node with a pole and magnet