Help needed with a circuit driving magnets

Hello everyone,
I am an Arduino and electronics newbie, and I’d need your help with a project I am working on.

Look at the attached sketch of the project I am currently working on. It is a circuit that controls 4 different magnets (in the image they are shown as motors, but they should be magnets). As you can notice, the power supply for the magnets (circled in red on the left side) is completely separate from the Arduino which is just taking care of the shift register on the left (74HC595). I want to keep the two circuits separate because of the magnets need something like 32V and between 500ma and 1amp of current. The 4 magnets are driven by two L293D.

Now, the problem I am trying to solve is that even when the Arduino is not giving the command to power the magnets (via the push button), I see the L293D and the magnets drawing some power from the power supply (something like <=200ma), not much, but sufficiently to heat the L293Ds even when they are doing nothing. I’d like to find a way to stop the power supply when not needed (i.e. when the switch button is not pushed).

I have thought to use either a relay or a mosfet transistor to control the power supply to the breadboard, but that’d imply having common ground with the Arduino circuit which I would like to avoid (I tried to have common ground with the Arduino and I fried a couple of shift registers because of that!)

Am I seeing this completely wrong? Or do you have any suggestions?

Thank you in advance for any help!

All the best,

Fab.

It is nearly impossible to interpret that Fritzing diagram. They are a terrible waste of everyone's time.

Please post a hand drawn schematic of the basic circuit (for just one magnet).

You should be able to turn the magnet on and off completely with the L293D, so get that basic one magnet circuit working before putting the rest of it together.

Verify that there's a connection between the power rails indicated by the blue circles. On many breadboards these have to be jumpered manually - as opposed to the smaller gap indicated by the smaller light blue circle.

Can anyone tell me if there is a common ground in that pic.
Really hard to tell from here.

ballscrewbob:
Can anyone tell me if there is a common ground in that pic.
Really hard to tell from here.

No there isn’t.

I’ll upload a simplified schematics with less components soon. Thanks for your feedback.

Ok, look at the image below, it is simplified and everyone should be able to understand it. As you can see, the power given to the motor is completely independent by the power given to the shift register:

I am also attaching the same image if you need a higher resolution.

Eager to know your thoughts. Thanks.

Hand drawn schematic diagrams, with IC pins labeled according to function, are much more useful, and waste less of your and our time. Please do not post any more Fritzings.

But it is obvious that the connections to the L293D are wrong. For one, there is no common ground between the motor driver and the Arduino. What is the 595 IC supposed to do?

Finally, breadboard tracks burn if subjected to motor currents. Breadboards are for logic circuitry only.

jremington:
Hand drawn schematic diagrams, with IC pins labeled according to function, are much more useful, and waste less of your and our time. Please do not post any more Fritzings.

But it is obvious that the connections to the L293D are wrong. For one, there is no common ground between the motor driver and the Arduino.

Finally, breadboard tracks burn if subjected to motor currents. Breadboards are for logic circuitry only.

Well, I am very disappointed by your reply.

First of all, as I said, I am a newbie (not sure to be though at this point!)

Second, the circuit works and the motor turns even if there is no common ground between the L293d and the Arduino because the shift register is driving the L293D. The breadboard I am using is rated 5amp. The 595 IC is supposed to drive 2 L293D for 4 magnets as described in my first post above.

Third, I don't think I need to post a more detailed graph with the name of the components and their function because I think anyone can easily understand the function of those two only components (shifter and L293D).

Fourth, and finally, a little more of politeness wouldn't hurt. I don't want to be afraid to post my inquiries here scared to be mistreated.

Thank you.

If the circuit works, your circuit diagram is wrong.

You are asking for help, from volunteers. If you don't want to provide the information required to help you, post on another forum and don't waste our time.

This is an example of a useful and correct schematic or wiring diagram for a motor and L293D. Notice the required common ground.

jremington:
If the circuit works, your circuit diagram is wrong.

You are asking for help, from volunteers. If you don't want to provide the information required to help you, post on another forum and don't waste our time.

This is an example of a useful and correct schematic or wiring diagram for a motor and L293D. Notice the required common ground.

I will post on another forum. Enjoy your time.

fablau if you are still around start with the links below.

Could you also take a few moments to Learn How To Use The Forum.
Other general help and troubleshooting advice can be found here.
It will help you get the best out of the forum in the future.

Occasionally we get a little grumpy as not too many people read the important posts (AKA stickies)

I don't mind fritzing for some of the simpler stuff but a lot of people hate them.
A lot of noobs start out with fritzin until they realise it has some limitations and that's why we prefer even a hand drawn one over of those.

ballscrewbob:
fablau if you are still around start with the links below.

Could you also take a few moments to Learn How To Use The Forum.
Other general help and troubleshooting advice can be found here.
It will help you get the best out of the forum in the future.

Occasionally we get a little grumpy as not too many people read the important posts (AKA stickies)

I don't mind fritzing for some of the simpler stuff but a lot of people hate them.
A lot of noobs start out with fritzin until they realise it has some limitations and that's why we prefer even a hand drawn one over of those.

Thank you for your kind and polite reply, really appreciated!

I do understand, of course. Ok, sounds good, I'll see if I'll be able to post a better schematics about this issue, but I think I found a solution to it already.

Thank you again for getting back to me in such a nice way.

All the best,

Fab.

Hello everyone,
I am an electronics newbie, and I am working on an Arduino project involving the use of electromagnets.

The electromagnets I am using are custom made and at 20v they draw about 90mA. I'd need to be able to make them run up to 32v for my application, which means they can draw up to 150mA at that voltage.

Now, I'd like to create a custom made L293D Motor Driver Shield similar to this one:

http://wiki.sunfounder.cc/index.php?title=L293D_Motor_Driver_Shield

But I'd need to be rated for voltages up to 32v, or maybe even a little bit more for safety (35-36v?) (that one is rated up to 16v). I know that L293D chips are rated up to 36v, so they should be ok to be used. But I have no idea about the rest of the circuitry that'd need to be "upgraded" (i.e. resistors, capacitors, etc). Keep in mind that with two L293D I can drive up to 4 magnets at 32v drawing a total of 600mA when fired at the same time.

Here is the schematics of that shield (also present on the webpage above):

I could easily reproduce the same exact circuit from that schematics, but, as I wrote above, I'd need to modify it to be rated up to 35-36v.

Thank you in advance for any feedback on this. I already looked anywhere for an answer to my inquiry and couldn't find anything around.

All the best,
Fab.

The last guy why tried a higher motor voltage blew up all the 16volt electrolytic caps.

Just replace them with 40volt or 64volt types, and you're good to go.
Don't try to power the Arduino through the shield a that voltage (remove the jumper).

But why a (bi-directional) motor shield for a (uni-directional) solenoid.
Mosfets, or a TPIC6B595 shift register could be a better choice.
Can parallel two TPIC outputs for higher current capability.
Leo..

Wawa:
The last guy why tried a higher motor voltage blew up all the 16volt electrolytic caps.

Just replace them with 40volt or 64volt types, and you're good to go.
Don't try to power the Arduino through the shield a that voltage (remove the jumper).

But why a (bi-directional) motor shield for a (uni-directional) solenoid.
Mosfets, or a TPIC6B595 shift register could be a better choice.
Can parallel two TPIC outputs for higher current capability.
Leo..

Thank you so much Leo!

Is that really it? Same farad values? Please, let me know.

Then I'll do what you have suggested.

About your question, I need to use L293Ds (or anything else able to invert the direction of the output) because the electromagnets I use (custom made) need to be able to both "attract" and "repel" in my application.

Any more ideas are very welcome!

Thank you again very much.

Best,
Fab.

It seems only the two motor supply caps (C7, C8) need to be replaced.
The remaining electrolytic ones are logic supply caps.
See this thread, image in post#3.

Not sure about the eight motor noise suppressor caps.
Those yellow or blue 100n through-hole caps are usually 50volt.
You will soon know if they have a lower voltage rating :slight_smile:
Leo..

Actually the post number 8 by jremington should really answer your question and help you.
Just read the diagram carefully and apply it to your circuit.

You really need that common GND.

A solenoid or electromagnet is the device with a coil. Without context a magnet means just a permanent magnet.

@fablau

TOPIC MERGED.

Giving you these links AGAIN please use them.

Could you take a few moments to Learn How To Use The Forum.
Other general help and troubleshooting advice can be found here.
It will help you get the best out of the forum.

ballscrewbob:
@fablau

TOPIC MERGED.

Giving you these links AGAIN please use them.

Could you take a few moments to Learn How To Use The Forum.
Other general help and troubleshooting advice can be found here.
It will help you get the best out of the forum.

I am sorry, but I don't understand. I have read everything carefully before to post the new topic and found nothing about "similar topics to be merged". I thought the second topic wasn't really related to the first one, that's why I created a new thread. I am quite confused.

I am really afraid to post here anymore. Sorry guys, but I think I will really find a different forum to post on. The environment here is too tense for me.

Good luck to all.