Understand the key characteristics you need to take into account when developing RFID hardware to design your own battery-free RFID sensor tags.

We’ve already mentioned how RFID hardware is all about selecting the proper components for your solution. This requires you to understand perfectly what your solution requirements are so be clear in your specification phase or your development will most probably fail.

RFID hardware: R-Meter MA10 schematic

RFID hardware: R-Meter MA10 schematic

Component selection

Once you have clear specifications there are four different areas you need to look at:

  • RFID chip. This is going to be the key component in your design. You probably know the sensors you want to use quite well so they are not the challenge for you. The RFID chip however, you will need to understand how it works.

When you develop with an RFID chip, you need to understand what the amount of energy you can harvest for the rest of the components is. Unlike other power sources, the RFID will give you a variable energy depending on different situations. It is your duty to understand how much energy you will have available in your specific application as read range, output power from the RFID reader, reader antenna and tag antenna gain, materials involved in the system, etc. will impact the energy you can harvest.

As an example, with an ANDY100 chip from Farsens you can harvest around 10µA@2.5V continuously when working at 2W ERP, 2.7dBi tag antenna gain and at 2 meters distance in free air (not anechoic chamber). Changing any of the specifications above will directly change the amount of energy harvested by the chip.

  • Sensor. The sensor is important in your design as this was the reason why you actually entered into this development.

We can’t give you much information about this component since this is specific to your needs. One of the biggest recommendation we can give you though is to check the dynamic power consumption if you are using a digital sensor. A bad assessment of the dynamic power consumption will lead to a wrong design of the startup circuit and the inability of the sensor tag to actually take a measurement.

  • Microcontroller. This is an important component as its selection is nothing but trivial. The fact that you are under a tight energy budget means you are limited regarding the features microcontrollers offer. The most common features to look for are:
    • Power consumption – active
    • Power consumption – Idle
    • Wake up time
    • Memory space
    • Available GPIOs
    • Processing speed

Once again, if you do not control the dynamic power consumption of the microcontroller – it will depend on your firmware of course – you will not be able to balance consumption and performance properly.

  • Rest of components. There will be other components that are required for the correct performance of your tag. These are more common in low power electronics though, not that specific for RFID systems.

These ‘rest of components’ will basically be devices to help you design a good startup circuit for your solution.

Keep in mind that selecting a sensor that works directly with the RFID chip will allow you to design an easier tag – not requiring the microcontroller.

However, depending on your solution you may want to use a microcontroller to deal with other things such as buffering. We’ll discuss about when talking about firmware development.

For more information about read range in RFID systems download the ‘Develop your own battery-free sensors like a pro‘ free eBook.

Develop your own battery-free sensors

Develop your own battery-free sensors