Which hardware, firmware and software considerations will you have to take into account if you’re working on battery-free RFID sensor design?
As we have discussed, a new sensor will require changes in three areas.
Unluckily, these three are linked and a change in one of them will drive changes in the other two so the correct implementation of the sensor requires a good level of understanding of both how the RFID chip works and the specifications you want from the tag.
Let’s dig deeper in what this means and how to implement these changes:
Hardware will be all about taking decisions on which components to use so you guarantee that the system works. Amongst others, these are the key things you should think about:
- Dynamic power consumption. It is important you understand that your sensor, microcontroller and other components (when needed) need to have an average power consumption lower than the energy harvested by the RFID.
However, that’s not enough for the system to work properly. The dynamic power consumption of each of the components needs to be addressed. The design may require a start-up circuit to prevent the system from entering into oscillation modes.
This is completely specific for each sensor and microcontroller, as well as the application – lower data rates may allow for higher power consumption by using a bigger capacitor for example.
- Internal data processing. Be it at the RFID chip side or the microcontroller side, you may want to process part of the data. This is often required when you want to increase the sampling rate from the sensor but not the data transfer rate from RFID tag to reader.
While the actual code developed accounts as firmware, the actual selection of the components falls under hardware. Depending on your requirements, it may be difficult to find all the specifications you need for a component to be implemented in a battery-free tag.
Firmware will probably be the most creative activity in this development.
If you are thinking about a digital sensor with SPI communication direct to the RFID chip, you can forget about it. There’s no firmware for you to develop and information will go directly from sensor to tag. This is simpler but won’t always be good news. For example, you can have higher sampling rate from the sensor than data rate from RFID chip to tag, meaning you are losing data points.
When you implement a microcontroller, you may well go the simple way and transform the sensor data into SPI to send to the RFID chip or you may want to do more. Using the same example as above, if the sensor has a higher sampling rate than what the RFID chip can transfer, you may want to design your solution with a buffer to allow sensor data to store and the RFID chip to continue to transfer data by accessing that buffer.
Your newly designed proprietary battery-free sensor needs to receive the correct commands from the RFID reader in order to operate correctly.
Luckily, our RFID chips work with EPC C1G2 commands – no custom commands are required – so you will be able to use any EPC C1G2 reader in the market.
That being said, it is important to say that not all readers work the same. You’ll need to figure out which one allows you to get the results you desire. Some of them will allow you to get faster data rates while others will allow you to improve the duty cycle of the power transferred – check our free eBook ‘The Essential Guide to developing RFID Sensor Software‘. It’s up to you to understand which one offers you the best balance for your application.
For more information about read range in RFID systems download the ‘Develop your own battery-free sensors like a pro‘ free eBook.
More to come on each of these in the coming posts. Stay tunned!