A simple controller for vAg in double run emulsions

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Nodda Duma

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This post would probably fall under the category of "advanced emulsion making"

A key aspect to making modern double run emulsion (i.e. graded Iodide core/shell emulsions) is measuring vAg as a feedback loop to control the rate of salt addition and keep vAg constant during precipitation.

If you are handy with Raspberry Pi and basic circuits, you can come up with a rather straightforward controlling circuit which measures vAg of your emulsion.

Not wanting to reinvent the wheel, I did some internet searching and discovered a circuit already designed (and posted only a couple weeks ago!) to perform a very similar function for controlling pH of fish tanks:

https://learn.adafruit.com/reef-pi-guide-5-dosing-controller

This would be incredibly simple to adopt to emulsion-making purposes. Of course, instead of measuring pH as an input to control, obviously you would measure vAg and adjust the conversion values for our specific needs.

I'll play with this in the future, but thought I would post so others could enjoy. The article includes all the components and the detailed steps necessary to build the controller.

Cheers,
Jason
 
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Nodda Duma

Nodda Duma

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Making the actual measurement is a separate problem to tackle, but one which is wonderfully detailed in your book. I posted the link to the control system here as a note for my future self, and for anyone else interested in double run emulsions which of course requires a feedback controller. The link above is a very simple and easy to implement example.

I'm more interested at this time in better controlling the precipitation stage of my single run emulsion. I pump in an initial amount of silver nitrate, hold it, then pump in the rest. The timing will be more accurate than turning the pump on and off manually. Not that exciting, really. Just dorking around with programming a Pi board.

Double runs for me are way down the road, but I figured I'd find a controller that would cover possible future need.

Cheers,
Jason
 
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Photo Engineer

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I don't really like the Pi board due to its construction. But anyhow, beware that with double run, you cannot run Iodide + Bromide when in control.

PM me if you want to take this offline.

PE
 

iandvaag

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No, please don't take it offline! (or if you do can you cc me too?) I've been working (very slowly) on making a feedback control system for controlled emulsion making and I've been reading with interest. I'm going with an arduino though. It sounds like I'm basically at similar point as Jason: increasing precipitation reliability using a pump with a SR emulsion. I think I've finally got the pump controller part mostly working, and I'll be doing some tests over the holidays.

Another step for me is to figure out how to get data readings through the RS232 port on the back of my pH meter (to be used as a high impedance volt meter) and to write a program for the control. I just wish I could have a bit more spare time!
 

AgX

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I find this interesting too. But I guess there are more members around who like me only learned via Apug of the existence of devices as Arduino and Rasberry Pi and are thus quite ignorant.
 
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Nodda Duma

Nodda Duma

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I find this interesting too. But I guess there are more membrers around who like me only learned via Apug of the existance of devices as Arduino and Rasberry Pi and are thus quite ignorant.

It doesn’t matter what or how you learn, as long as you keep learning!

Raspberry Pi’s are like the modern day version of the Commodore 64. The Commodore was a tinkerer’s computer.
 

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I prefer Arduino for some situations. As for computer interface, Radio Shack had a fine VOM which had a computer interface. I have it running on my computer and it can monitor vAg quite nicely. I have done it, but not under control. I observed the feedback manually and controlled it.

I don't have time to look it up, but the meter costs about $65 and comes with the interface software and a temperature sensor. You have to build the silver electrode and buy a double or triple junction Silver/Silver Halide electrode, and if you want accuracy you need to build a salt bridge.

PE
 
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Nodda Duma

Nodda Duma

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I became interested in Raspberry Pi and Arduino boards when I (a) started getting interested in Python as a substitute for Matlab at home, (b) realized how huge public domain support is for the computer and microcontroller, and (c) when computer-building gifts for the kids turned out to be Raspberry Pi's (and in 7th grade my daughter learned to program Pi boards) and Arduino microcontrollers.

BTW, the Pi boards and Arduino both support analog voltage inputs, so I think it'd be even simpler than that.... just have to generate the appropriate transfer function or look up table for the pump motor control.
 
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