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Add-on board: 24-bit ADC, 18-bit DAC

A project log for A Versatile Labtool

A cost effective, multi-pronged data acquisition tool to turn your computer into a workbench for science and electronics experiments.

Jithin 06/28/2015 at 22:210 Comments

This was a breakout board built for trying out the ADS1248 24-bit ADC as well as the AD5680 18-bit DAC. The final version should include opto-isolation and a standard 20-pin header compatible directly with the expansion slot on the base board among other things.

+2.5, -2.5 volt regulators ( TPS76325, TPS72325 ) are present in order to provide reference voltages for the ADC.

In order to get data from the ADC using a simple python script, the SPI as well as the power supply connections must be made to the base board. Following which, carefully perusing the datasheet will let us construct Python functions such as

def writeRegister(self,regname,bytes):
	I.SPI.start(csn) #lowers Chip select
	reply=[]
	reply.append(I.SPI.send8(0x40|regname))
	if len(bytes):
		reply.append(I.SPI.send8(len(bytes)-1))
		for a in bytes:
			reply.append(I.SPI.send8(a))
	I.SPI.stop(csn) #raise chip select
	return reply

This board has not been fully tested , and I expect the built in excitation current sources will come in very handy for measuring voltage drops across resistive loads such as RTDs and load cells.

A 22-BIT ADC board with three MCP3550 on board. Two of these have level shifted inputs, while the third is a direct in.
A ref196 has been placed as the voltage reference IC.

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