Chimaera

Digital Signal Processing Unit (DSP-F3)

The Chimaera DSP unit is a mixed-signal board. It uses a 32bit ARM Cortex M4 microcontroller from STMicroelectronics (STM32F303Cx) clocked at 72MHz. Of the available peripherals, we use the FPU, ADC1, ADC2, ADC3, SPI1, I2C2, DMA1, DMA2, USB, several TIMERS and a couple of GPIOs. The main circuitry runs at 3.3V, driven by a low-drop-out voltage regulator (LM1117). To leverage the MCU, we use a hardwired UDP/TCP/IP/PHY chip from WIZnet (W5500) which takes care of all the low-level networking and is communicated to via SPI1. There are two EEPROMS (24LC64, 24AA025E48) which store the MAC address, the configuration and the sensor calibration data of the Chimaera. To switch the multiplexers on the sensor units we use a 4-bit counter (74HC163).

The analog part of the board consists of 10 analog inputs which provide connection points to connect up 10 (surprise!) sensor units, leading to a maximum of 80cm of sensor array (160 sensors). Those analog inputs go directly to three in parallel running 12bit ADCs embedded on the MCU. In order to reduce noise, The ADC circuitry on the MCU is driven by a dedicated low-drop-out voltage regulator (MCP1703). The sensor units are connected to by 3 wires (Ain, GND, Vout).

Finally there are a RJ45 MagJack and a mini USB socket. USB is solely used to flash the MCU with new firmware. There are also two SPST buttons to reset the board and to get it into flash mode. The whole board needs to be driven with Vin = 6VDC @250mA minimally. The amperage of the whole Chimaera is calculated as 250mA + n*110mA, where n is the number of sensor units. The board’s dimensions are 80x44 mm.