Simple PWM Stirplate Controller

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Well I wanted to come back here and close the book once and for all on the issue I was having. In case someone stumbles into this thread a few months from now and wants to try their hand at a 556 design instead of Rocketman's 555 they might as well have all the facts.

The long and short of it is that my original circuit back on page 4 works perfectly fine as it was, minus the shared heatsink I installed between the MOSFETs, which coupled their drains. The MOSFETs don't even need heatsinks, so had I just left them alone in the first place I never would have had an issue. This morning curiosity got the better of me so I removed the 7805 from the circuit, put everything back the way it originally was, and tested it again. Everything worked great with independent control of the two fans and I can use either 5V or 12V as my DC input with good results. The current surges and/or voltage swings do not affect the 556 in any negative way, at least in my case.

I also wanted to thank both thargrav and rocketman one more time for their help in troubleshooting my mistake. If anyone wants to see pictures of my finished product I stuck them in the "show us your DIY stir plate" thread rather than cluttering up this one: https://www.homebrewtalk.com/f51/show-us-your-diy-stir-plate-228400/index14.html#post4398482
 
R1 = 22k resistor
R2 = 100k pot (use the middle and one of the end pins)
R3 = 4.7-10k resistor
C1 = 2.2 micro-Farads capacitor
Q1 = N-channel MOSFET
All components available at mouser.com.
The 555 can be a cmos 555 (LMC555) or a regular 555 if you like. Q1 is any standard MOSFET (or NPN transistor, like 2n2222) with a current rating of at least whatever your motor is going to suck (mine draws 100 mA). The diodes are standard silicon diodes. The two wires going the pot are connected to its middle pin, and one of the two end pins (which one determines if turning clockwise increases or decreases speed). I have drawn two options for the output stage. I prefer option 1 because MOSFETS are much more efficient, but they can be hard to find in physical stores.

Make sure your Q1 is oriented in the right way (D,G,S for MOSFET, or C,B,E for NPN) by looking at the data sheet or packaging for the component!

Rocketman768 This looks like something that I could actually pull off. Thanks for your posting. But, I'm not an EE and am a little lost on the mouser site trying to narrow down your parts list to the thousands of flavors available. Is it too much to ask for catalog descriptions/#'s of the parts list? Also on the diagram are two diodes that I don't see on the list. What flavor of these should I use?

Thanks,
Tom
 
Rocketman768 This looks like something that I could actually pull off. Thanks for your posting. But, I'm not an EE and am a little lost on the mouser site trying to narrow down your parts list to the thousands of flavors available. Is it too much to ask for catalog descriptions/#'s of the parts list? Also on the diagram are two diodes that I don't see on the list. What flavor of these should I use?

Thanks,
Tom

I don't like to do this, because parts are always going out of production and changing numbers and stuff, but this should get you started.

R1: MF1/4DC2202F
R2: P160KNP-0QC20B100K (Knob)
R3: MF1/4DCT52R4701F
C1: UVY2A2R2MDD
Q1: NTD4909N-1G
555: NE555N
Diodes: 1N4933-E3/54
 
This is a nice twist on the stirplate design. Having OCD about such things, it bothers me too that the low end is lost -regardless of whether or not I need it for my design, it's still a loose end.
 
The low end is lost because at the low range the PWM circuit is not providing enough power to start the motor. The solution to this is to tune the PWM until the motor is barely running at the lowest setting, which is probably somewhere around 10% - 20%.
 
To tune the PWM you would experiment with different value resistors in series with the POT until the motor just starts at the lowest setting, then you would permenently install the resistors. The value depends on the motors you use in the project.
 
So far this looks great to me, but not entirely friendly to those who are not electrical engineers perhaps. I understand the components, I know what diodes and timers are. I understand pots and resistors and caps. I need to look into how to wire circuit boards a little and I will try this. Are you guys using perfboards? I saw someone mention that, isn't a perfboard usually used for wire wrap? Can you solder to it? Never actually used one. I do not understand how to read electrical diagrams too well I guess.


I feel like what we need is a close-up diagram of the actual components on a board with the pot, resistors, 555, psu, etc displayed and how it is wired. I'd be willing to do this graphically as soon as I understand it better myself.

Something like this:

OBVIOUSLY THIS HAS NO ACCURACY AT ALL AND IS MERELY AN EXAMPLE

diagram.jpg
 
J187,
I think what you're looking for is something like the diagram I posted back on page 4: https://www.homebrewtalk.com/f51/simple-pwm-stirplate-controller-219121/index4.html#post4393542.

Granted that diagram was for a dual circuit design based on a 556 timer, but it shows every single wire and connection on the breadboard and I'd wager a non-engineer could split that diagram conceptually down the middle and wire up a 555. To be clear, on a 555 pins 1-8 are not the same as pins 1-8 on a 556, but that aside the rest of the circuit would be wired identically after accounting for the correct pin numbers. Here's the pin mapping that would have to be done for a 555 based diagram:
My 556 Pin Correct 555 Pin
1 7
2 6
3 5 (no connections anyways)
4 4
5 3
6 2
7 1
8 8

For what its worth, my opinion would be to stay away from perf boards and wire wrapping or soldering unless those activities are something you enjoy / are good at. It's just so easy to wire up a breadboard since all you have to do is cut and strip wires and press them into the holes. The signal distribution and power busses are done inside the board for you. If you wanted I could draw you up a breadboard diagram just like the one on page 4 but for a 555 circuit. It should only take a few minutes to modify the one already posted.
 
I'm going to try this. My current stir plate has the issue that there is only a narrow band in which I can control the fan speed. And I'm using a LM317. Thanks for posting the part list and such. I have experience with building electronic stuff (used to be my hobby before I took a job in the computer industry) but finding suitable parts is always a challenge.

Kai
 
Thanks rocketman. Even if the numbers have changed, at least i can figure out what the new item number will be. This will be fun!

Rocketman - successfully got the parts on the list from Mouser. As I am putting this together from your build diagram, I noticed that there is an unlabeled diode/resister? that bridges the motor leads. Is this an R1, 1 or 3, or a diode?

If I pursue the Mosfets option #1 that you recommend, do I need the R3 resister?

Thanks
 
The diagram shows the mosfet leads as DGS but the datasheet typically seems to be GDS. should the wiring be made to adhere to the pins as shown on the datasheet? In other words does G always goes to position 3 on the 555 regardless of it's position on the mosfet? Thanks
 
In other words does G always goes to position 3 on the 555 regardless of it's position on the mosfet?
Yes. Manufacturers like to be special unique butterflies about package pin positioning sometimes.
 
Works for me :)

I did have 2 challenges, though. I got a Arduino board like this one: http://www.mouser.com/Search/ProductDetail.aspx?R=T030081virtualkey99990000virtualkey782-T030081 but didn't know that there are connections between the holes. So I ended up spending a while on troubleshooting why the design sucks so much power :)

Then I connected R1 to GND by mistake and had to think hard how this circuit works and found that C1 never charged.

But I can't get the motor speed down to really slow. I think this is because R1 is fixed and the min pulse with is thus fixed by the time it takes to charge C1 through R1. I saw many designs that charge C1 through one side of the potentiometer and discharge it through the other side. this way you can get the pulse with really short.

Have you tried this? I'm giving this a try.

EDIT: I did try this and it works well. I'll keep it that way. But it takes 1/4 turn to get the motor moving since the very short pulses are not strong enough.

Kai
 
Your lingo makes me wonder why im studying computer engineering. I hate v dividers... Dont get me wrong, they work great and have many applications, i just hate studying and being tested on them.
 
I built this on a bread board using the values on the front page. My fan goes from a medium speed to a fast speed. I need to get it to go slower. Either i have hooked something up wrong or i need some different values on some of my components.

I have double checked the drawing and i fell like everything is connected correctly. I used the values on the drawing. The only doubt i have is the capaciter. The capaciter has a long wire and short wire. I hooked the short wire to ground and the long wire to terminal 6. Is this correct? The data sheet said the long wire is positive.

I am guessing i need to go up on either r2 or c1. Any suggestions?
 
I built this on a bread board using the values on the front page. My fan goes from a medium speed to a fast speed. I need to get it to go slower. Either i have hooked something up wrong or i need some different values on some of my components.

I have double checked the drawing and i fell like everything is connected correctly. I used the values on the drawing. The only doubt i have is the capaciter. The capaciter has a long wire and short wire. I hooked the short wire to ground and the long wire to terminal 6. Is this correct? The data sheet said the long wire is positive.

I am guessing i need to go up on either r2 or c1. Any suggestions?
 
The only doubt i have is the capaciter. The capaciter has a long wire and short wire. I hooked the short wire to ground and the long wire to terminal 6. Is this correct? The data sheet said the long wire is positive.
That's correct.

I built this on a bread board using the values on the front page. My fan goes from a medium speed to a fast speed. I need to get it to go slower. Either i have hooked something up wrong or i need some different values on some of my components.

I am guessing i need to go up on either r2 or c1. Any suggestions?
Before you start changing anything, I'd suggest you finish mocking up the whole thing (glue your magnet to the fan, etc.) and actually try it out with your flask/jar/vessel and your stir bar. Right now with no load the fan might seem to be spinning too fast, but the added mass of the magnet, the stir bar, and the liquid in the flask will help slow the motor down.

If after testing your set up the fan is still spinning too quickly, then you can try adding resistance in series with R2 or try Kaiser's modification a few posts up.
 
changing the way the capacitor is charged and drained is key to be able to change the pulse width from 0 to 100%. I ended up building it like this:

StirPlatePWMCtl.gif


you need one more diode but don't need R1.
It works like a charm.

Kai
 
I will give this a try. I currently have my stirplate to where it goes slow enough to use. However it does not turn off completely.

What is the purpose of sinking both the .1 and 22 mf capacitors from the source to ground?
 
well, heres my take on it so far...



Let me know what you think
 
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Bumping this old thread, hopefully someone's can help me out.

The mosfet linked by op is not made anymore, so does anyone have a part # for an equivalent?
 
I realize this thread is a few months old but here's to hoping someone is around to listen. First let me say thank you Rocketman for sharing such a simple to implement design!

I built upon this design to make a dual-stirplate using identical components to yours with the exception of a 556 dual timer instead of the 555. I wired up each half of the 556 just like your 555 and it's working great with one minor exception.

The only issue I'm having is that if I turn *either* potentiometer knob then *both* fans respond. I can't figure it out as the 556 halves are supposed to be completely isolated with the exception of Vcc and ground. I've triple checked the circuit and aside from the 556 itself there's nothing crossing from one half of the breadboard to the other so I can't figure out why this is happening.

I've attached a wiring diagram for my breadboard in case anyone thinks they can help. Also the higher level circuit schematic in case you need the 556 pinout. This isn't the exact physical wiring of my board in it's final state, but it does match electrically. I made this easy to read, symmetrical version for pre-planning the circuit, but in the final layout I spread the components out and relocated some connection points for easier routing inside my box. Again though, it's electrically representative, just easier to read.

Thanks in advance to anyone that can point out what I've done wrong. If we can figure this out I'd love to post more information about my stir plate in case anyone else is interested in building a double.

Edit: So after posting this I got the idea to study the circuit diagram a bit instead of just studying my breadboard looking for mistakes, and I have a guess at the problem. For the record my capacitors are non-polar electrolytics because that's all Radioshack had. As such I'm guessing the voltage at Pin 2 is bleeding down through the "left" cap, back up through the "right" cap and affecting Pin 10 (or vice-versa). I should be able to prevent this with another pair of diodes, one between each cap and ground, to prevent any flow between those halves. Does that seem to make sense? I think I'll swing back through Radioshack tomorrow to give it a try as I can't see any other method for voltage on one half of the circuit to cross over to the other. If anyone else sees anything please let me know.
I tried making this dual stir-plate that @Magialist shows in the two attachments, and had trouble.

Has anyone else made this dual stir-plate successfully? I'm sure I just have something wired wrong, but I could only get one fan to spin and when I adjusted the Pot, the speed didn't change.

I do see a couple differences between this design and the original post in this thread. There's an additional Resistor in the original post, and an additional diode in this post.

I wanted a dual stir-plate because I'm going to be brewing 10-gallon batches, probably splitting into 2 different fermenting buckets and maybe trying 2 different types of yeast, or simply having enough yeast starter for 10 or more gallons.

I did have the drains isolated from each other both electrically and physically (Not connected at the heat-sink).

I was just hoping for some confirmation the design as-is in the two attachments in the post from @Magialist is correct for a dual stir-plate, even though there are differences between it and the original post.
 
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changing the way the capacitor is charged and drained is key to be able to change the pulse width from 0 to 100%. I ended up building it like this:

StirPlatePWMCtl.gif


you need one more diode but don't need R1.
It works like a charm.

Kai
Hi !! It's an old but GREAT and very usefull thread !!!

My diy stir plate is controled by an LM317 and it's frustrating not to be able to rotate the fan at lower speeds.... I read the entire thread and will definetlly try rocketman768's schematic.

I'd also like to make the change proposed by Kaiser (changing the way the capacitor is charged and drained) but, as an eletronic noob, I cannot do that without the schematic/picture and it's not available anymore. Any help ??

Thanks in advance
 
Hi !! It's an old but GREAT and very usefull thread !!!

My diy stir plate is controled by an LM317 and it's frustrating not to be able to rotate the fan at lower speeds.... I read the entire thread and will definetlly try rocketman768's schematic.

I'd also like to make the change proposed by Kaiser (changing the way the capacitor is charged and drained) but, as an eletronic noob, I cannot do that without the schematic/picture and it's not available anymore. Any help ??

Thanks in advance
Try this: http://braukaiser.com/wiki/index.php?title=PWM_Coltrolled_Stir_Plate_Design
 
Man, I'm really having trouble building this thing. I had a dual stir plate wired up with just one side and it worked....sort of. It only came on at high speed and I could only slow it down a little bit and eventually the fan just stopped spinning. I think I may have poor quality breadboards (cheap, from China).

Then, I fried a 556 chip.

Has anyone successfully built one of of these dual/556 stir plates?
 
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