06. Selecting Your Hydrometer Type - larry-athey/rpi-smart-still GitHub Wiki

NOTE: The RPi Smart Still controller will work just fine without either of my hydrometer options. You just won't be able to use features such as ABV management, minimum flow monitoring, or distillate temperature monitoring to increase condenser cooling if your distillate goes over 24C/75F (which is a common problem with T-500 columns).

In this repository, you will see that there are three different types of hydrometer projects. By default, the system uses the LIDAR Hydrometer Reader. This is the easiest one to build and can be added to any existing traditional parrot and glass hydrometer. The E85 Sensor Hydrometer project really only still exists here for informational purposes, I strongly recommend against using it since E85 sensors are highly unreliable.

The Load Cell Hydrometer is accurate and reliable IF you accurately calibrate its weight settings using test distillate that is between 20C/68F and 21C/70F, and use it in an environment of the same temperature range. This is because ethanol will slightly vary in density depending on its temperature and a load cell will expand and contract depending on temperature as well. This could likely be remedied by adding a compensation temperature sensor attached to the back end of the load cell and additional code to dynamically calibrate it.

I came up with the LIDAR Hydrometer Reader after a number of people told me that the Load Cell Hydrometer was just too complicated for them to build and calibrate. I kind of expected this because we live in a world of instant gratification and a dying awareness of basic physics. People with component level electronics knowledge and skills are also a dying breed. The disappearance of Radio Shack and local electronics supply stores really killed off a lot of this.

As for the most common question I get about this...No, this is not the same thing as George Duncan's "Talking Parrot Head" closed source Arduino based project. Yes, it works on the same principal, but George's requires a PVC tube to be mounted to the top of your parrot which makes it bulky and top heavy. Mine uses the same type of sensor, but it's mounted to the side of the parrot overflow cup and aims up at an angle to a 3D printed disc at the top of the hydrometer.

The main problem with George's design is that it expected the hydrometer's scale to be a specific length. Not all hydrometers are equal, I have one with a 122mm scale and one with a 135mm scale because it's smaller in diameter. This is why my LIDAR Hydrometer Reader has calibration functionality. Shorter scales work better because they reduce the possibility of erroneous readings caused by reflections from the stem when the reflector is higher.

The LIDAR Hydrometer Reader is temperature compensated and uses a precision ethanol density lookup table. While a LIDAR sensor only measures in millimeters and lower ABV marks on an ethanol hydrometer are less than 1mm apart, this reader can get you within +/- 2% ABV of the actual reading, even on lower proofs - and that's even with the offset caused by weight of the reflector.

Calibrating the LIDAR hydrometer reader

  • Attach the reflector disc 20mm above the 100% mark on your hydrometer. Use a small about of rubber cement to lock the reflector in place. Don't use too much because it can affect the accuracy of the hydrometer. Just make sure that the disc is level and you'll be fine.

  • Click on the Calibrate Hydrometer menu item under the Management menu. Confirm that your LIDAR hydrometer reader is communicating with the RPi Smart Still controller. The data in the bottom frame of the page should be updating every 10 seconds.

  • Use a syringe to slowly fill your parrot with water until the 100% mark of the hydrometer is even with the center tube of the parrot. Click the button on the screen to calibrate the 100% mark.

  • Continue filling the parrot with water until the 0% mark is even with the center tube of the parrot. Click on the button to calibrate the 0% mark.

Calibrating the flow sensor

  • Do a few test fills/drains of the flow sensor with 80 proof vodka and a syringe. It's important that the inside of the flow sensor contains humidity and ethanol vapor during calibration.

  • Plug the bottom drain hole of the flow sensor. Use a piece of electrical tape or whatever else you have on hand. Then fill the flow sensor again to the top of the overflow tube inside. Click the button to calibrate the full value of the flow sensor.

  • Unplug the bottom drain hole, allow it to drain, and then click the button to calibrate the empty value of the flow sensor. You may want to do a few test drains to get a grasp of where the actual empty reading is because the capacitance will continue to decrease the longer that it sits empty. You should only see about 30pf difference between full and empty.

If you choose to build the load cell hydrometer, you need to switch the RPi Smart Still controller over to use that one instead. This will change the Calibrate Hydrometer page. This is done by directly calling a specific URL.

http://ip-address-of-your-pi?hydro_type=0

Change the zero at the end to a one to flip things back to use the LIDAR Hydrometer Reader instead. This toggle is intentionally not built into the user interface.