Developing your own battery free strain gage is at your hand. Start testing with the VMeter platform to make your development easier.
The VMeter is a development platform we provide for development engineers and people that love ‘Do it Yourself’ challenges. It basically allows you to have a battery free tag with the potential to monitor the voltage level between two pins.
Strain gages are generally built into a Wheatstone bridge to create a circuit that varies its voltage output based on the deformation the strain gages are suffering. By using the correct formulas, that voltage can be transformed into meaningful values in terms of force or deformation.
Creating a circuit that allows for a battery free strain gage
The great advantage of the VMeter tag is that not only it has the two pins (V+ and V-) to monitor the voltage of your circuit, it also includes a power supply to avoid having to use an external power source. This effectively converts the strain gage in a battery free and wireless device that works with EPC C1G2 RFID readers.
However, as with all battery free sensor tags, the key is to manage the existing energy wisely. You will have to make sure the power requested for the signal conditioning circuit embedded in the VMeter tag plus the power consumption of your circuit are kept low enough.
This may force you to use high value resistors in series with your Wheatstone bridge to lower the current going through your circuit, making your accuracy lower than you expected. The balance between the power consumption and performance is going to be your hardest challenge.
Modifying hardware and software for specific applications
You may also want to configure your battery free strain gage to perform in different ways. Some of you will want to monitor deformation in a single direction while some of you will want to monitor deformation in two directions.
This affects the signal conditioning circuit inside the VMeter. It has an ADC which zero value can be set in its lowest value – this allows you to monitor only positive voltages – but you can also set the zero value in the center – so you can monitor both positive and negative voltages.
This requires some modifications in the VMeter hardware which imply basically modifying resistance values in the PCB.
However, the changes in hardware will also affect the software so bear in mind that the free testing software we provide in our website will not support directly your changes in the hardware. It is important that you understand what changes you are applying so that you can convert the value to the correct voltage and deformation you are looking for.
If you’re developing a battery free strain gage and think we could be of help contact us at firstname.lastname@example.org any time.