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Add-ons : High resolution ADCs

A project log for Python Powered Scientific Instrumentation tool

A multi purpose lab tool accessible by simple Python functions, and capable of studying a wide range of physical phenomena.

Jithin 06/14/2015 at 19:100 Comments

Tested the AD7718 24-bit ADC with a custom PCB.

AIN1-AIN4 have been broken out into pin headers directly , and can be used as unipolar inputs/differential pairs.

AIN5-AIN8 will be used to measure bipolar signals. The inputs for these are attenuated and buffered using high precision Op-Amps OPA2277(offset<10uV , drift<0.1uV/C ), and then level shifted.

The StickVise that Hackaday handed out a couple of weeks ago has turned out to be incredibly useful since I use surface mount parts a lot

Fig : Schematic

Now that its functionality has been reasonably tested in terms of software control, and noise spread is below 100uV, an opto-isolated version can be made which should give much better resolution. I hope to post histograms and other characterization results soon.

Unipolar inputs were tested using unbuffered voltages from the 12-bit DAC of the main board.

Differential inputs were checked out using a Peltier plate used a voltage generator.

The main aim of this add-on board for now is to serve as a calibration tool for all the analog inputs on the main board. The AD7718 will first be calibrated against a 6.5 digit standard DMM from Keithley, and then be used as a calibration tool.

The PCB features the REF196 voltage reference, as well as an AD5680 18-bit DAC(as yet untested )

A PCB for a 22-bit ADC MCP3553 is also on its way .

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