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I’ve been bumbling my way through grasping the beauty of using voltage dividers to create virtual grounds so that I can use a single power supply as a power source to the op amps.  In the back of my head, I hear Ryan’s (SparkysWidgets) warning that I’m leaking current into the bath which makes measurement difficult at best and more likely impossible.  But I need to understand all this stuff better, including different configurations for virtual grounds with the goal to use a single power source while handling an AC Signal as it makes its merry way through op amps.

The Goal

The goal of this post is to better understand the impact of design choices on designing virtual grounds

Thanks to Those That Go Before

Every day I think about the things in my life that I am thankful for.  There are so many things.  One is the sharing of knowledge from exceptionally smart and caring folks.  Today’s thank you goes to:

  • Chris Gammell – Chris is an exceptional teacher/guide who tirelessly walks me through electronic design concepts and implementation.  He has a knack for teaching in a way that makes me passionate to learn more.  I do recommend his Contextual Electronic courses.  I took them and learned a lot.
  • Ryan of SparkysWidgets – If it wasn’t for Ryan’s open source design of the minipH and miniEC, I would not be able to make the progress I have made on the pH and EC Circuits I work on.  Ryan has been exceptional in giving me insight and advice on my circuits.  His stuff is great!

Overview

I discussed in this post how I designed for a single power source in order to handle the negative pH readings of the AC Signal.  While this design should work ok for the pH circuit, it will not work for the E.C. circuit.

Why?

The Challenge Using the VGND of the pH Circuit

The major difference between the AC signal – in the case of pH, the pH voltage and in the case of EC, the Wien Bridge Oscillator – is shown in this diagram I found from this site:  

Voltage Divider With Load Explained

Recall the (glass) characteristics of a pH probe mean the AC Signal will act as a high impedance load. SpakysWidgets notes: “A typical probe has an impedance of anywhere between 50Ω and 500MΩ.”    The Wien Bridge is built on the wires and components on a PCB or bread board and so acts as a low impedance load.

The pH probe adds pretty much 0 load to the circuit. This is not true for Wien Bridge Oscillator.  The more load, the less the output voltage will be.

Consider this example where this is no load (as is the case with the pH circuit):

No Load Divider

Ach – the more I learn the less I seem to understand.  But just keep swimming..just keep swimming!

 

 

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