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 paper 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 112mm 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.

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.

PRO TIP: If you are using the LIDAR Hydrometer Reader and a hydrometer with about a 112mm scale, you can likely get by with the default configuration by floating your hydrometer in your parrot with water so the 50% line is even with the top edge of the center tube. Then adjust your reflector at the top of the hydrometer up/down until the RPi Smart Still controller shows 50% on the screen. It should end up 20mm above the 100% line. Also, be sure that you never use any kind of glossy paper for your reflector and remember that dark colors work better than white. Otherwise, you will experience unstable readings.