SPI ADC with Signal Conditioning

There are a lot of real world parameters that cannot be directly read or measured by computers, nor by any electrical device. Transducers and sensors are used to translate different physical parameters into proportional voltage output. This output voltage of the sensors/transducers is analog and cannot be read by digital electronics equipment. Analog-to-Digital converters (ADCs) are often used to translate these analog signals from sensors into a proportional binary value for use with digital electronics processing equipment like microcontrollers.

Unfortunately, it is not always that easy to connect the output of a sensor to the input of ADC. There is a wide range if operating voltages and variety of output voltage levels and ranges that a transducer/sensor can produce that may not be usable with digital electronics hardware that usually works at 5V or 3.3V. It may not even measurable by a low resolution ADC. Therefore, invariably all sensors/transducers need special circuitry for "signal conditioning" that can amplify or attenuate the signal to measureable levels, and also shift its voltage level so that the system can focus on the desired range of output.

The SPI ADC with signal conditioning Wing will have 2 analog channels with onboard signal conditioning support. I intend to use National Semiconductors ADC082S101, ADC102S101, ADC122S10 dual channel 1 Msps serial SPI ADCs. Two stages of Op Amps will be used - first stage will be powered by sensor supply voltage and will shift and amplify/attenuate the signal to ADC level. Second stage will be powerd by ADC reference voltage and will buffer and clamp the output voltage of first stage.

Features

• High speed 4-wire SPI interface at 16 MHz suited for a Wing for the Butterfly Platform
• Each channel can measure input voltages from a few millivolts to 18V
• Support for separate sensor voltages for each channel
• Separate gain/shift settings with presets for each channel
• Each channel can be read samples at 500 ksps maximum, making it usable for audio sampling applications as well as low frequency oscilloscope
• Resolution can be 8, 10 or 12 bit depending on the ADC device used

FPGA support

While this SPI ADC Wing can be operated by any standard 16-bit SPI or SSP interface (at minimum 8 MHz) from the FPGA or a microcontroller, a special peripheral core for the FPGA is being developed that will allow using the ADC through simple register interface. It can emulate ADC register interfaces of a variety of popular microcontrollers including AVR, PIC, most of 8051 and ARM variants allowing it work seamlessly with existing software base.

Current Status

The SPI ADC with signal conditioning Wing PCB's are currently in planning stage.

• Board Design - Pending
• Board Manufactured - Pending
• Board Assembled - Pending
• Preliminary Testing - Pending
• Board completely Verified - Pending
• Board available in Store - Pending