CY8CKIT-022 CapSense® Liquid Level Sensing Shield Kit Guide, Doc. #: 002-09825 Rev. **
19
Kit Hardware
2.4
Functional Description
2.4.1
Two Sensor Flexible PCB
The signal ratio from the two sensors (RX0 and RX1) provides a low cost method of determining
liquid height. The pattern shown in
is similar to a backgammon game board, and is
therefore referred to as the “backgammon” pattern. A third transmitter (TX0) sensor is provided to
support the CapSense mutual capacitance scanning method, and can be connected as a CapSense
transmitter. If CapSense self capacitance scanning is used, then the TX0 sensor is not required and
must be grounded to avoid interfering with the RX0 and RX1 sensors. The flexible PCB comes with
a non-conductive double sided adhesive already applied. To use the sensor, it must be adhered to
the flat side of the supplied liquid container and attached to the kit shield board.
Figure 2-10. 2RX Sensor Pattern
2.4.2
12 Sensor Flexible PCB
Each segment of the 12 sensor (RX[0:11]) pattern shown in
provides an incremental
portion of the total liquid level. While the “segmented” pattern requires additional sensor elements
and pin compared to the 2RX version, it allows liquid level resolution to be customized for each
design. For use with CapSense self capacitance scanning, only the sensors RX[0:11] must be
connected to the PSoC CapSense I/O pins and the TX0 sensor can be left floating or tied to ground.
When CapSense mutual capacitance scanning is used, all of the RX and TX sensors must be
connected. A small ground plane hatch between the RX and TX sensors is provided to help direct
the electrical field into the liquid to increase sensitivity.
Figure 2-11. 12RX Sensor Pattern