Welcome To: MinieC Hardware Repo!!
Note: This is for the MinieC Hardware Version 1.1 Branch
This is a revised layout of the 0.2 version. It is a major revision featuring some part changes to make the unit better quality overall. Wein bridge oscillator may still be changed to a phase shift style still unsure of this. As of now the basic operation is a Wein Bridge Oscillator creating a fairly stable sine wave with a little clipping on the negative rail. The DC current through the probe is into the noise floor of my Bench DMM, sub 400nA range, with an AC current of 71uA K1 probe in ~300ppm Tap Water. AC currents at 90KuS are still only about 2.8mA which is very impressive since this is way outside of the K1 probe's range. The other change is a super diode configuration with a buffer stage after for final output. This removes the diode drop and give a better DC output.
Basic schematic is split into sections
- Charge Pump section
- Op-amp switched to quad-amp
- Diode peaker, is now configured as a SuperDiode with a buffer stage as final output
- Analog Front End - AC oscillator stage with a variable gain stage based on SUT conductivity
- 12bit ADC
Board Layout Info
Form Factor based on standard Mini formfactor (1.1" x 1.1")
- Standard 2.54mm pitch header and Grove style connector
- Able to work with Kcell constant probes .1, 1 and 10
- Layout is pretty much the same as other MinieC versions just changed to accommodate quad op-amp
Just a quick list of current issues
- Clean up sine wave just a touch, maybe add fq selector (would be a 10x range deal)
- Take a look in MinieC's Firmware Repo For Arduino!
- Check out my USB eC/TDS interface LeoEc for a powerful and easy to use USB eC/TDS Probe interface!
Usage of MinieC example code is very easy. As of now you read the peak off the output and form a linear map based off a one or 2 point calibration at each Kprobe level that will be used. a simple set of equations based on this map will give you the eC/TDS and Salinity(of specific salts). SUT is treated as an unknown conductance/ohms) and is one tap of a op-amp gain voltage divider. Some useful conversions; G=(Vout/Vin)-1 and R = Rf/G, R = 1/eCE-X where X is conversion to micro siemens based on probe K cell constant. I.E KCell 1 (1uS/cm) is 1E-6, K10 1E-7 and .1 is 1E-5. conductance 1/ohms and PPM=eC500.
This is a fully open source project released under the CC BY license
MinieC by Ryan Edwards, Sparky's Widgets is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
Based on a work at https://www.sparkyswidgets.com/portfolio-item/miniec-i2c-ec-interface/