wiki:DeadProjects

This page will document a biological compound sensor being developed for the research group of Profs. Mohanty and Eramilli.

This device will use a proprietary sensor chip to measure the concentrations of various biological compounds in an aqueous solution.

Open Issues

  • Mechanics - connector type and pinout for cell connection

proposed 8-device prototype. What are the units?

Prototype 1 Specifications

  • Generate a fixed AC stimulus signal of 10mV at 17Hz (sinusoidal)
  • Provide a DC bias for 'V(DS) on which AC stimulus is superimposed

with a range of -2V to +2V. Set in 5mV or smaller steps, absolute precision to 1mV desirable.

  • Provide an analog switch to route the above 'V(DS) combined

AC/DC signal to one of eight electrodes.

  • Output a separate DC source for 'V(GS) with same

specs as for 'V(DS) above. This will set the potential of an electrode immersed in the solution.

  • Provide two additional side-gate bias voltages with an output

range of -5 to +5V (Precision? Step size?)

  • Provide eight analog switches for each side-gate bias voltage

to route the above signals to the desired device.

  • Measure the DC and AC currents through the sensor. The AC current will

be measured using a phase-sensitive detector, converted to a DC signal, and digitized with an ADC.

Future versions may also have variable frequency and amplitude for the AC stimulus.

Analog Circuit Implementation

The analog interface electronics will be implemented on a custom PC board which will have a connector on which the sensor cell can plug directly.

Please refer to the  block diagram The blue lines show the wiring on the device itself, or its mounting PC board. The blue squares represent connection points to the electronics.

Four DC bias voltages are buffered and driven to the device as shown. Three analog switches for each of 8 devices allow bias signals to be selectively applied to one device at a time.

Readout is via a current-sensitive op-amp circuit, a phase-sensitive detector, DC amplifier and ADC.

Control and Interface

We currently plan to purchase an off-the-shelf embedded controller and A/D interface board. See links below for some likely options. We would provide software on the embedded computer to support setting the analog switches and bias voltages, and measuring the current with an ADC.

A simple TCP/IP server or USB equivalent would be provided, with a very simple DEMO program running on a PC to show functionality.

from technologic systems looks like a good bet.

  •  TS-ADC16 board would provide DAC (12-bit) and ADC (16-bit) and digital I/O functions –

 preliminary manual

alternative I/O board with 12-bit DAC/ADC functions.