Imported from GitHub: alberto-battistel/Teensy-EIS · commit 6c8f6eb · license GPL-3.0

Description

Transform your teensy 3.6 (pjrc.com) into an instrument for electrochemical impedance spectroscopy.

README

Analog front-end

The analog front-end interfaces the Teensy to the instrument (potentiostat). It serves as conditioning of the signals. It mainly provides low impedance for the inputs, level shift (Teensy is 0-3.3V), and some degree of rejection for ground loops (still to understand a bit better). It also features an independent power stage (USB compatible) to handle bipolar signals.

Signal conditioning

At the moment the conditioning is build on 4 INAs 128 (Instrumentation amplifiers) from Texas Instruments. They are flexible building blocks featuring low noise, low distortion, easy level shift, and high impedance inputs (10 GOhm). Two INAs are used to buffer, level shift, and shrink the DAC (digital to analog converter) of the Teensy and the other two are for level shifting of the inputs of the two ADCs (analog to digital converter). Analog filtering can be easily attached to the INAs. 4Input-1Output_board contains the full design (schematics and printed circuit board layout with bill of components) to build up the signal conditioning part. It is a very flexible board. We also employ it for additional reference electrode probes in electrochemical cells or to break groud loops.

Power

The power stage is based on a DC-DC converter (NMA0515SC from Murata). It takes 5 V as input and provides +/- 15 V. It may be connected to the Teensy and take power from the same USB cable, but we did not test this yet. The bipolar voltage is used to power the INAs. The positive rail is also used to hold a normally open signal relay (MT2 Relay from AXICOM). This relay is controlled by a digital pin of the Teensy through a transistor (2N3904) and it is necessary to cut the DAC line from the Teensy toward the instrument so that unwanted signals cannot be injected (for example when you turn on the Teensy...).

State of the material

At the moment the schematics and the PCB layout signal conditioning part is available in 4Input-1Output_board, but we may come out with a more practical design later. Complete_analog_front-end.pro (KiCAD project in Design_schematics) contains the functional design of the project with the fundamental connections between the Teensy and the analog front-end and the power stage.