Welcome To: Handheld Water Quality Sensor Meter!!
Note: This is for the HHWQS Hardware Version 0_1 Branch
HHWQS Hardware Design Files in EAGLE. Layout is finally finished but the board is untested and in a beta state. Although it is build from proven designs, the Sparkfun powercell which is a LiPo charge manager and 5v dc-dc boost converter handles the bulk of the battery management. Layout is based off preferred datasheet placement and layout (Performance might be better with large planes for heat dissipation). Analog front ends are build from the well proven Mini line that I have designed, the eC portion is isolated. One of the best features of this unit is the ability to select the type of Ion Selective Probe on the pH/Ion end. This means that pH, ORP, DO, Nitrate and most other Ion type probes are usable. I don't know of any handheld unit on the market(as of 04/2014) that has this ability!! To add to the features both an eC front end and a 1 wire temperature probe input are available. The design is meant to fit the Hammond 1553T enclosure and will use a 4d system 2.5inch tft display unit initially as I source cheaper more viable screens for output.
Schematic had to be split into sheets due to too many parts, each major portion is on a sheet.
- USB, MCU, 1Wire temp and Flash digital section
- pH/Ion Selective Analog Front End - 3V reference with +/- 5V rails (no clipping of signal!) paired with ADC with proper filtered input(See TI video more quick and dirty http://youtu.be/8lxCo1U07Bs)
- eC Analog Front End - Isolated so not to interfere with ion selective front end. It is important to note when checking voltages on the test points to make sure to only reference from the ISO GND pad
- LiPo Battery Management - Consists of TPS61200 dc-dc boost converter IC, MCP73833 charge management IC and a MAX1704X LiPo Fuel Gauge IC. The parts are chosen from the Proven Sparkfun Powercell (With Oleg of Circuits at Home responsible for the boost converter portion) but the charge management IC has changed with recommendation from Microchip to use another for future designs. The fuel gauge should let us use less resources on the MCU let the ic handle all the math and measurements!
Board Layout Info
Form Factor based on Hammon 1553T enclosure fullsize PCB drawings
- MCU placement nearer to USB side to shorten the hishspeed lines (long I2C to AFEs is the tradeoff)
- LiPo battery connector placement is not ideal from a mechanical standpoint, ideal from an electrical.
- AFE contain test points at various keys spots on the topside, remember eC AFE is Isolated and therefore must be reference from ISO GND
- pH AFE is now an Ion Selective AFE with the ability to adjust the gain prior to offset to known values from a simple digital pot
- the Guard ring around the High Z input is still intact including the digital pot portion (layout of this section is absolutely critical to consistent operation)
- eC AFE is completely isolated effectively making both the pH and eC isolated units (due to the battery operated design, unit is inherently isolated)
- Standard Arduino Digital and Analog pinouts are broken out to ensure rapid prototyping of additional components (BLE, Solar, Wifi or different screen and input tech) this is derived from my Leo line of WQS interfaces.
Just a quick list of current issues
- Maybe a half board would be better overall due to cost consideration condensing layout would be no problem
- untested so I guess there is a lot of unkowns right now
- Take a look in HHWQS's Firmware Repo For Arduino!
- Check out my USB pH interface LeoEc for a powerful and easy to use USB pH Probe interface!
Usage of HHWQS 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
HHWQS by Ryan Edwards, Sparky's Widgets is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
Based on a work at https://sparkyswidgets.com/portfolio-item/HandheldWaterQualityMeter