Electronic Design
PIC Module Runs Off RF Power

PIC Module Runs Off RF Power

Microchip and Powercast have joined together to deliver a unique wireless solution that provides power and communication over the air. I had a chance to check out the Lifetime Power Energy Harvesting Development Kit for Wireless Sensors (Fig. 6) that is just one of the Powercast development kits available. One of the demo boards (Fig. 1) can be powered remotely by a simple 915 MHz, 3W power transmitter box (Fig. 2). A single transmitter can power any number of remote units. It has dual DC power inputs. Different size antennas (Fig. 3) can be used to capture different amounts of power. One is directional. The other is omnidirectional. It is also possible to charge rechargeable batteries, use super-capacitors or thin-film energy cells to provide more power at peak times depending upon the application.

The kit includes a Powercast P2110 development board with Microchip module (Fig. 4). The Microchip sensor module includes an 8-bit PIC microcontroller and a 2.4 GHz wireless 802.15.4 adapter. The module can detect temperature, humidity and light. The Powercast board provides power to the module. Of course, it gets that power from the transmitter box. A PICkit 3 is included for programming and debugging the modules. The Microchip module can be easily replaced with a custom module.

The P2110 module has a P2110 chip that can provide up to 50ma of current. A boost converter delivers a constant voltage level up to 5.25V. The default output is 3.3V. A power status signal is provided and a host microcontroller can turn off power using another pin. An external power cap is optional.

The kit also includes a Microchip XLP 16-bit development board (Fig. 5) An 802.15.4 PICtail adapter plugs into this board providing a three node system. This board is designed to be the gateway and is not powered by the Powercast system. Instead, it uses a conventional power brick.

The sample application is installed on the XLP board and the two sensor modules. Testing the system was simply a matter of plugging everything together. This includes the power to the XLP board and the power transmitter. I hooked a PC serial port to the XLP board's serial interface to access the bundled application. The interface provides to the packet scanner application that displays data being sent from the wireless modules.

Microchip's MPLAB development tools are included in the kit along with the Microchip MiWi protocol stacks used with the 802.15.4 transceivers. The sample application source code is provided and is a good starting point for further development. The trick is actually keeping the power requirements within the limitations of the Powercast power supply.

Low and high power antennas are provided for developers to experiment with. The sample application is designed to handle up to 8 MiWi nodes. They do not have to be powered by Powercast but that would be the typical deployment approach.

I should have popped open the box sooner. I though it was going to take a bit more time to get the system up and running. As it turned out, the demo app was running minutes after plugging everything together. I was able to change the code on the sensor module to provide additiona packets within an hour. It did help that I have used MPLAB for ages and I had already worked with the MiWi stack using other Microchip boards.

From a software standpoint, the kit will good when using Microchip's protocol stacks. It should be a trivial task to switch to one of their other 802.15.4 stacks including ZigBee if necessary. Switching to another microcontroller is possible as well but it would require a switch to another wireless protocol or use of ZigBee. MiWi is used only by Microchip.

The Powercast board uses a standard header to creating a custom module should be easy. Determining the mount of power available will require a little more experimentation because there are more variables involved. Distance and obstacles between the modules and the power transmitter affect the amount of power available to a remote device. Likewise, the cycle time of the application will also affect the system requirements.

If you are interested in checking out Powercast's power harvesting then this is the kit for you. The power antennas that come with the kit are removable but a typical application would have these built into the system. They are actually just circuit boards so it is possible to have a single board solution. Powercast can help with an integrated antenna board design.

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