glass and electronic

[Hannah]

Hi evryone, I am a student glassblower and am looking for some advice about a project I am on. My plan is to create a vessel that has rings around the outside that when I place a test tube into the ring it sets off a trigger and a water pump goes off on a timer. I am a beginner at the whole electrical side and although this may be complex i am looking forwards to learning and getting this to work. So far i have an arduino, a solenoid valve(NC), a peristltic pump and a very basic understanding of what to do. any advice, no matter how complex will be greatly appreciated. thank you!! 

[Andy Chee]

Is there anything unusual about this proposed vessel with rings?

For example, will this vessel be heated?  chilled?  contain corrosive liquids?  or does the vessel have an unusual shape?  what material is the vessel made from?

Your trigger could be anything from a microswitch, magnetic reed switch, ultrasonic range detector, to video camera.

The more details about your proposed setup, the better and more specific advice we can give.

The Arduino timer is by far the simplest and most obvious part of this project.  A timer program is trivial to implement on an Arduino.  The wiring to the pump should also be relatively simple, but will need details on the pump specifications.

[Hannah]

Hi Andy, thanks for your reply. to answer your questions, theres not much unusual about the vessel and rings. nothing will be getting heated up or chilled or and corrosive liquids just water. every thing is made form clear furnace glass.  i have put up a sketch of what i am hoping it will look like.
the pump is a peristaltic pump that takes 12 V and 5w. hope this helps, any more questions i will answer to the best of my knowledge.
Thanks

[inse]

I cannot imagine any other solution than to mount microswitches to sense the presence of the test tubes.
But there are two problems: you will have to route wires along the vessel and the only way to mount anything to the glass is glueing and that may be neither reliable nor aesthetical.
I don’t have experience with image recognition, but that’s probably beyond arduino capability

[I wanted a rude username]

Adding to Andy's excellent overview, you might want to step back and consider whether this could be an XY problem. That is, we can help you with the electronic side of such a device, but is the overall idea for the device itself the best solution to your project? Some related questions:

• Do lab technicians actually like rings for retaining test tubes?
• What do test tube holders normally look like, and why do they look like that?
• How would the rings or other holders be attached to the vessel?
• Glass vessels normally don't have steel set into them, why is that?
• What are the ergonomic implications of having test tubes distributed around the vessel instead of in a rack?
• How will the vessel be held: by clamps, a stand?

Of course, none of this is to suggest you shouldn't do it the way you've envisioned it. Your drawing has a lovely aesthetic to it, which laboratory glassware often lacks. This is more of an engineer's perspective ... asking the question, is the device something that the end users would actually enjoy?

[inse]

Latest after the drawing it was clear to me that this was more like an artistic installation than laboratory equipment - no?

[Analog Kid]

I think it's safe to say that this is an art project, certainly not any kind of lab equipment. (Unless the OP tells us otherwise.)

Since the test tubes will be held by rings, which I assume are metal (and therefore must be glued to the vessel somehow), how about some kind of proximity detector, like elevator buttons? Thin wires could be attached to the rings and glued to the glass in a somewhat unobtrusive way, and a circuit could detect the test tube being placed by capacitance or some other method, yes?

Sounds do-able to me. Dunno exactly how, though.

[Gregg]

I would first try the reed switch and magnet approach as previously suggested by Andy.  For a prototype, the reed switch glass tube could be glued (hot glue to test the concept) to the vessel and a small magnet glued to the bottom of the test tube.  The magnetic flux pattern and its relation to the reed switch is important.

There are lots of small relay modules available from the usual suppliers of Arduino components with opto isolation to isolate the pump power from the delicate reed switches.

[Hannah]

so first of all yes this is more of an art project rather than actual lab equipment. the rings are too going to be made from glass which are hot attatched through the making process. this is just one piece in this project with a whole backstory but saves me explaining it all. the vessel is held by a clamp stand around the neck. the device doesn't have a user/operating goal but its about the filling up of the vessel by having a response to external stimuli, in this case represented by the test tubes. im not bothered about seeing wires and the operational componants either. I have also been given a sort of basic starter kit for this including a breadboard, a mosfet, 5v regulator, 555 timer, and a load of resistors. forgive me for the lack of understanding but i have given it a go with trying to create some sort of functioning circuit out of these all but i am getting very confused with it all. like i said i am before even beginner level at this all and have some very dumb questions to start with which watching video of how to set this up arent answering so any sort of advice would go a long way. i know its not great but at the minute soldering isnt an option so how  do i connect the mosfet to the arduino and so forth? thanks for the brilliant replies so far, i appreciate the help )

[Andy Chee]

Let's experiment with the 555 timer first, and put aside the Arduino for now.

Try building this project, which may be along the lines of what you want to achieve:

http://www.learningaboutelectronics.com/Articles/555-timer-monostable-circuit.php

The circuit can later be refined to accommodate appropriate triggers and your water pump, but experiment with the 555 monostable as it is presented.

The circuit can also be implemented in an Arduino program sketch which potentially offers more flexibility (or complexity!), but as I said, let's just play with the 555 for now.

[inse]

I would suggest to start with the most challenging part: sensing the tube insertion.
Do research on micro switches and think about how to attach and wire them.
Reed contacts may be too fragile and also require correct orientation of the magnet, which is undefined at round objects like test tubes.
And if this is solved, go on with the electronics

[Manul]

Given the level of experience, I don't think it's time to play with the 555. You need to start with sensing. The most simple way would be a microswitch. You may be able to find smaller ones. Or maybe a force sensor mounted between a vessel and a ring, so you can detect weight of a tube (more advanced).

[inse]

All the artistic aura gone 🥲

[Manul]

All the artistic aura gone 🥲

Another idea would be to mount a microswitch together with a ring, so the thickness of a tube sliding in activates it. Might be more aesthetic, not sure.

[inse]

All glass, hand crafted <headscratch>

[jpanhalt]

I enjoy glassblowing, and while not a professional, while in grad school, I stood in for the temperamental departmental glassblower who resigned.  I read your posts and still have no idea of what you are trying to make.  Can you try explaining?   Attaching test tubes to the outside of a large round flask, if done in that order, might be a lot more difficult than it seems.

[Manul]

I wonder, how good it would work if small force sensing resistor would be glued to the wall and then the ring would be glued on top... Probably doable, but could be finicky.

[antenna]

You might be able to disguise the wires as some decorative copper pattern made of foil tape on the glass.  Perhaps on those tape foil traces could be some kind of IR proximity sensor.  I wonder if there exists some sort of IR led/detector in a small SMD package.

[Analog Kid]

I'm not sure why nobody else here seems to like my capacitive-sensing idea: I can't say for sure it would work, but it seems to me that if it did work it'd be a hell of a lot simpler than any kind of switch (mechanical like a microswitch or a reed switch).

Could it work? I'm thinking of the big illuminated elevator buttons that you don't have to push in order to operate them. Don't those work by using a small RF field and measuring the disturbance when someone's finger gets close to it?

And would that be within the capability of a DIY n00b here (no disrespect intended to the OP)?

[antenna]

I'm not sure why nobody else here seems to like my capacitive-sensing idea:

Seems bulky and complicated.  Maybe it wouldn't be, but it seems like a lot of hardware for a simple job that a contact switch can do. 

It wouldn't have to be a premade switch either.  A strip of foil tape around the neck of the test tube would do it..

[antenna]

If it were a simple contact via foil tape, it could be AC coupled so it don't hold the trigger on the 555. The trigger cannot be held low or the timer output cannot change.  Since the trigger pin needs to be pulled down, but only momentarily, run the trigger line to one of the contact points on the ring and the other side of the contact points goes to ground via a capacitor.  Since the cap starts off discharged, setting the tube in the ring will close the contact, and since the capacitor takes time to charge to the trigger voltage, it will pulse low instead of being held low. 

One foil strip around the test tube neck, one broken foil strip on the ring from the 555 to ground with a cap on the ground side.  Simple.

[inse]

The rings are formed from glass, so each one will be individual - no chance that it will make a reliable (if any) electrical contact.
Don’t propose complicated electronic solutions like capacitive sensing to a novice.

[Analog Kid]

I'm not sure why nobody else here seems to like my capacitive-sensing idea:

Seems bulky and complicated.  Maybe it wouldn't be, but it seems like a lot of hardware for a simple job that a contact switch can do. 

Bulky and complicated? Far less than any kind of switch: the only "hardware" needed would be a wire or two.

But what I'm not sure of at all is the electronics required. Anyone care to sketch out for us the circuitry required?

Hey, if this idea isn't feasible, then so be it.

[inse]

Here‘s the theory behind it: https://ww1.microchip.com/downloads/en/Appnotes/Capacitive-Touch-Sensor-Design-Guide-DS00002934-B.pdf
Here’s some product:
https://www.ebay.de/itm/226362062944?mkcid=16&mkevt=1&mkrid=707-127634-2357-0&ssspo=si_rstkxq22&sssrc=4429486&ssuid=UJEfguXdQ76&var=&widget_ver=artemis&media=COPY
Maybe it works, needs to be tried out…

[Analog Kid]

OK, thanks for that.

They show using a microcontroller (of course, Microchip). Any chance this could be done with a simpler circuit, say something based on a 555?