The overall board architecture is shown in Figure 1. It provides eight sensor channels for capacitive proximity measurements. The board is built around a TMS320F28069 microcontroller from Texas Instruments. This microcontroller is capable to do native floating point calculations and fast signal processing. The board is driven by a 5V voltage supply source that is either connected by Universal Serial Bus (USB) or by Controller Area Network (CAN). A linear dropout regulator provides a 3.3V supply to drive the microcontroller. The evaluation board is able to communicate with a PC using a serial-to-usb converter. The driver is available for many platforms and can be downloaded on FTDI’s homepage. The microcontroller can be programmed using a JTAG interface. Therefore, an XDS100 emulator is required (for example XDS100v2 14 pin JTAG emulator from Spectrum digital, TMDSEMU100V2U-14T).
2. Sensor Channels
A single sensor channel is shown in Figure 2. The evaluation board provides eight sensor channels. A sensor channel represents a generic interface that aims to support different sensor types. Each sensor channel has a USB port for the connection of a sensor board. A sensor channel consists of two connections for voltage supply, a connection to an MCU’s general-purpose-input/output pin (GPIO) and a connection that leads the sensor’s output to an analog-to-digital converter (ADC) or enhanced capturing unit (eCap) for analyzing digital signals. The GPIO pin is dedicated to be used as an enable signal for a sensor. The sensor’s output signal can be switched between the ADC and eCap, depending on the returned signal type.