I got a sample from Analog Device a while ago, the AD7176 24-Bit, 250 kSPS Sigma Delta multichannel ADC. It claims to deliver 22 noise free bits at 5 SPS. The reason I wanted to test it out is that it’s “recommended for new designs”, have the specs I need and has a TSSOP form factor that makes it manageable to solder by hand (0.65mm between the pins). Initially I didn’t get it to work. The problem having only one device, is that anything can be wrong. The device can be faulty, the connections/soldering can be bad, improper decoupling/grounding, poor communication with the processor. Or last but not least, the software might not work.
EasySMU (DC2591A) is a programmable-voltage/programmable-current
source from Linear Technology with accurate voltage/current measurement capability. Its primary purpose is to demonstrate a I2C address translator. However, it actually implements a 4 quadrant power supply using LT1970A Power Op Amp, DAC (LTC2655 16 bit) and ADCs (24 bit LTC2485) and some additional circuitry. It even contains a 24LC025 I2C serial EEPROM to store calibration information.
Therefore it is a perfect learning/reference/starting platform for me, even though it is limited to +/-12V and +/-40mA. I can use it as a preliminary hardware platform while developing parts of the “poor man’s smu” software and display.
I’ve just purchased a PDVS2 from ianjohnston.com (2018). It’s a battery driven precision voltage source based on LM399 (6.95V 0.5 ppm/degC shunt reference) and a 18 bit DAC9881. According to Ian, each shipped unit is: “…assembled & tested in-house, aged/burned-in for 120hrs and calibrated with a HP3458a 8.5 digit multimeter (Keysight Cal. 21/03/18) at constant ambient temp“. It arrived in a solid package that include a power plug (with wire ends) and a calibration card. Note that batteries (2x9V) are not included. As stated on the webpage: “Batteries are not supplied so customers must supply their own and we highly recommend 600mAH or better Li-ion PP3 batteries from EBC or Etinesan… These will give you 12-14hrs continuous use between charges.“.
I had a hard time finding such batteries in Norway. I did find some, but with only 2-300mAH. I ended up using standard 9V batteries (even if not recommended) for my initial test. Have performed a quick test using Keithley DMM6500 to measure the output. The Keithley had varmed up for 2 hours. The PVDS2 was just turned on (note that warmup period is recommended). The statistics show on the Keithley for each measurement are based on a few seconds data collection (>1000 samples).
Looks to be well within specs ! Note that V2 has improvements over V1. One of the most visible improvements is the added knob.