Liquid agitator for PCB chemicals

Hello to all,

This is a little project that I present here, not because of any great importance, but perhaps it will help another newbie, such as myself.

Based on Bill Marsden's PCB thread on this particular sub-forum, I started making my own PCBs.
After making a couple, I became agitated (pun intended) by the fact that every few minutes I'd have to go over to the tray and lift it a little to redistribute the fluid.

That got old, so I thought I'd make a little automatic agitator that would constantly, but gently, agitate the liquid over the board - so I could be doing other things. As a bonus, I thought I would try PWM on the motor so I could control the speed (didn't know much about PWM, only did steppers before).

So I took one of my trays, added water, and gently lifted it so that a wave was constantly going over the PCB, and had my wife measure the distance that was lifted - 1 cm. Then started my homework.

Here is the final product:

No, it is not "Thing" from The Addams Family!

I basically used THIS circuit, changed the potentiometer to 10K, and added an LM317 to provide 3V to the DC motor.

Here is the modified circuit diagram:

Hardware and electronics:
ABS plastic sheets and glue - TAP Plastics
555, LM317, IRFZ46N, pot, caps, resistors - Jameco
Bolt - Harbor freight
PCB - homemade
9V wall wart - All Electronics
3V DC motor, geared down - Servo City
Misc hardware, spacers, hinges - Non-Ferrous Fastener, Fastenal, Hobby Lobby

The potentiometer can change the speed a little.
The bolt in front allows height adjustment of the motor so it can push the top up from 0 to 1 cm.

HERE is a YouTube video of it working. I removed the sound track, it was windy that day.

The things I learned:
1. Very importantly, I learned about ABS sheet - had no idea it existed.
It's easy to cut (carbide blade wood saw) and glue, with the right "glue".

2. I learned a bit about PWM, and feel comfortable about using it in the future.

3. I learned that small DC motors come in standard sizes, voltages and currents, and can be swapped out.

4. I learned a bit about using the 555, and will put together some other basic projects with it.

Things I would do differently:
1. Use a bigger motor - even geared down, it groans when lifting the top. I'll probably change out the present one.
2. Change the cam on the motor to something thinner or use a rod to lift the top.
3. I'm probably going to add some Velcro to the top plate, and bottom of the tray - probably not necessary,
but it will hold the tray in position better.
4. I forgot to put an "on/off" switch

I'd be interested in hearing comments on how it might be improved.

I thought about making something similar way back when, even drew a crude diagram of it. Basically my thought was a tray on a small rod, to allow the tank to rock back and forth.

Another common technique is sparging, when you use an air pump and bubbles to agitate the liquid.

I don't know about the gentle agitation. What I do is agitate the etchant and PCB VERY vigorously.
A colleague of mine built an etching tank that sprayed hot recirculated etchant on to the PCB like a car going through an automatic car wash. Constant agitation and heated etchant dramatically reduces the time required to etch the board, to under three to five minutes

MrChips said:

I don't know about the gentle agitation. What I do is agitate the etchant and PCB VERY vigorously.
A colleague of mine built an etching tank that sprayed hot recirculated etchant on to the PCB like a car going through an automatic car wash. Constant agitation and heated etchant dramatically reduces the time required to etch the board, to under three to five minutes

Click to expand...

What source did he use for the pressure pump on the etchant? I haven't found a DIY/cheap one that can move Ferric Chloride.

Deja vu. I think we discussed this once before.
He used a peristaltic pump, the one that has rollers that squeeze the solution around a loop of tubing. Thus the etchant never comes into contact with the metal parts of the pump.

SPQR said:

HERE is a YouTube video of it working. I removed the sound track, it was windy that day.

Click to expand...

Nice work. I've also made an agitator. Based on an PIC16F628 and a ULN2003.

It looks like this.

nerdegutta said:

Nice work. I've also made an agitator. Based on an PIC16F628 and a ULN2003.

It looks like this.

Click to expand...

That looks very nice...larger volumes possible.
What do the microcontrollers control? The speed? The time?

SPQR said:

That looks very nice...larger volumes possible.
What do the microcontrollers control? The speed? The time?

Click to expand...

Thanks.
I can do fairly large boards, and large quantities.
The uC controls the speed of a steppermotor.

The next version, I will add a timer, buzzer and a LCD display. Redo the mechanical work, so I don't need the belt...

MrChips said:

Deja vu. I think we discussed this once before.
He used a peristaltic pump, the one that has rollers that squeeze the solution around a loop of tubing. Thus the etchant never comes into contact with the metal parts of the pump.

Click to expand...

Heh, I'm having Deja Vu all over again too. Didn't realize you could get enough pressure/volume to run it through a power spray from a peristaltic pump, though.

Update.

As I mentioned my first 3V motor was "groaning" when it lifted the lid, and after a while I noted that it stopped working.
Isolated testing with a 3V power supply indicated it had gone to better pastures - R.I.P.

I then tried THIS motor which looked a little stronger.
It was a LITTLE stronger, but didn't cut the mustard.
I put it out to pasture before it croaked.

Then I bit the bullet and tried THIS 3-12V motor, and changed the LM317 470 ohm resistor to 1.5k ohms to run it at 7 volts.

It works nicely now.

Lesson learned - test your motors first.

SPQR, how did you glue the corners of your box together?

Aha! There were to "most important parts" to this project for me.

1. The existence of flat ABS material
2. Learning about using the right "glues"

In another project I posted here I tried to make a box out of acrylic and it was a disaster because I wasnt' using the right "glue".

Since then I feel very comfortable with acrylic and ABC.

The "glue" is not really glue - it is solvent.
Just like when you are putting a PVC pipe system together, that stuff you put on the joints is not glue, but solvent - it dissolves the PVC on both pieces and "welds" them into a single piece.

I learned this from TAP plastics and their great videos.

HERE are some ABS sheets, and HERE are the solvents.

If you use the right solvents, it is EASY to put ABS and Acrylic together.
I know, I've tried three types of epoxy, odd glues, everything from Lowes.
The first time I used the solvent, I said to myself "Eureka! I've found it".

The videos are REALLY good on TAP.

painI guess my question should have been, how do you get the nice sharp right angles? I And get exactly fit on the end pieces?

And how do you hold it all together while gluing?

You can you clamps, just like in woodworking, but for small pieces, I just use my hands.
It's tacky almost immediately - hold for a minute and it will be fine.

Inject air into a defuser below the tray. Use a fish pump or 2 if necessary.

I join acrylic plastic (Plexiglas) using dichloromethane dispensed via a hypodermic needle.
Joints must be smooth and true, i.e. surfaces should align perfectly.
Hold joints together with whatever means, clamps, rubber bands, masking tape, etc.
Squeeze the dichloromethane into the joints. The solution will seep in by capillary action and the plastic pieces will fuse instantly. There is no time or opportunity for further readjustment or alignment. You cannot take it apart after the fact.

Sounds like a good technique MrChips!

Clamp and align it perfectly dry, then just apply glue and it's done!

The clamp and align is my big problem. I used to have access to a shear, I miss it. Cutting a straight line is harder than it sounds.

Acrylic cuts fine on a table saw (like a wood circular saw table) and most of those have guides etc to keep it lined up square and cut straight lines at right angles.

A plastic supplier I buy from just table saws the pieces to my dimensions and they come out pretty good!