THANK YOU RICK for your comment.  The night before I read your comment, I was talking to my husband about how writing this blog took time away from building stuff.  Rick’s comment is a KEY REASON I write the blog – to learn from others who have A LOT more knowledge than I have.  It is totally exciting to evolve a skill to a level in which the beauty of the mechanics combine with a design that …well, solves a problem.  I find Rick’s comment inspiring so….again, THANK YOU RICK.  THANK YOU.

I spent last week getting older as well as evolving my current design of the pinch valve.  So what are the results?

Frustrated EPIC FAIL



And then I thought…yah know what?  I’m stopping my current goal of automating calibration (meaning I’d need solutions/containers for pH4, pH7, and an EC calibration solution) as well as checking the pH and EC outside of the nutrient bath.  If I just leave the pH and EC probes in the nutrient bath, I don’t need any of this stuff.  Talk about a simplification.  I only got to this added complexity because I wanted to evolve my knowledge of valves.  AND I think logically the pH probe would degrade faster if it is always submerged within a bath full of salts smacking on it’s delicate membrane.  That and constant calibration would give accurate results.  But given the range of pH and EC values that are acceptable, I don’t need great accuracy…so bah-bye clean pH and EC probe.  Bah-bye always on calibration….back to what I was doing before…dangling the probes within the nutrient bath…

and yes…but wait…Rick then wrote a comment that interrupted this line of thinking.

Rick’s Comments

Rick noted:

  • consider changing the thickness of the tubing – Shore Hardness.  Now here’s something about learning without guidance…I was going to give this a twirl but 1) didn’t know googling “Shore Hardness” would evolve my knowledge on tube thickness.  And I didn’t know what kind of tubing to get.  Rick recommended this latext (surgical) tubing.

To explore this, I ordered:


  • try a shorter arm on the servo (increases the available torque).  Oh..right…yah!  Will do.  Again I question what I was doing during science classes.  


I assume I was taught this?  But in what context?  As I get older, it turns out context is so important to empathy and interest..yet I diverge.

Rick asked about using a peristaltic pump…and indeed, I have used these in the past.  I know how these work and yah, I could use it…I was hoping for something less bulky.  I would be using peristaltic pumps in pH UP, DOWN, and EC adjustments within the nutrient baths within the adjustment section of the Leaf Spa.  I have done this in the past but haven’t yet added auto adjustment.

  • consider a different design for the container/test tube (whatever) where the probe will be inserted to take a measurement. Rick’s comments are detailed and I might have misinterpreted, but this got me thinking.  Yah – instead of separate chambers, one block-o-food safe plastic with holes drilled in them where the solution will drip into.  Once measurement is done, use a servo to tilt the block 180˚ and dump the solution out.  The challenge I was thinking about was fluid flow when the servo is in rotation.  The potential of solutions intermingling – which is not what I want.  I thought at this point I could experiment with ways of directing fluid away from one of the holes….hmmm….

The above is my interpretation.  Here are Rick’s words: “Regarding your test chamber/test tube assembly … take a block of HDPE (high density polyethylene, say 1″ x 7″ x 5″, drill 5 (or more) round-bottom holes part way through, and then mount this drilled block on pivots, so you can use your existing servo to dump the contents into a waste pan after you calibrate. The round bottom hole can be created with a 1/2″ box core router bit (woodworking tools are very compatible with HDPE). HDPE is pretty insensitive to most of the chemicals you’ll be comfortable working around, is rated food-safe (FDA), and is inexpensive.The round bottom prevents gunk (highly technical term) from collecting in the crevice a flat-bottomed hole would provide.
When sampling your nutrient solution, you can tilt the test chamber 45°, have a channel milled on the side of the test chamber to route the nutrient solution back into the reservoir until you have flushed the tubing and have a good sample available. Stop the pump, rotate the test chamber vertically, and then fill, test, and dump (in this case you can choose to dump the tested nutrient solution back into the reservoir (slight risk of contaminating your nutrient solution), or dumping it directly into the waste pan (slight volume loss, but absolutely safest for the customers.”


Once I get the tubing in I will most likely give yet another go at automating measurement.  But always I will be thankful for the knowledge and thought process Rick provided.