Need solution for electromagnets project

[prabhubng]

Hello,

I am new to electronics I am trying to do a project but I am unable to find suitable design for it, I am using Arduino board for my prototyping, the project is, I made a matrix of 8x8 small electromagnets which is working with 12v and 250 mA, basically these electromagnets pushes a small neodymium disc magnets on other side.

I tried to drive this using 74HC595+ULN2803 combination for each column and I am able to drive them individually, but my problem is I need to also switch the power direction individually so that the electromagnet pulls the neodymium disc magnets back, now I am not able to decide how I can drive those individually with bidirectional power switch from code.

To get an idea this project similar to flip disc displays where the electromagnets try to push and pull the neodymium magnets so that the disc flips.

It will be really helpful if someone can give me suggestions over this issue and sorry for my bad English.

Thanks in advance,
-Prabhu

 

[blambrec]

Hi Prabhu,

Sounds like an interesting project. It's just off the top of my head, but maybe something like what I've drawn here is what you would be looking for....

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[prabhubng]

Hi Prabhu,

Sounds like an interesting project. It's just off the top of my head, but maybe something like what I've drawn here is what you would be looking for....

View attachment 87217​

Hi blambrec,

Thank you for your suggestion, I was thinking few other type of options:

1, Having two coils placed in one core and switching between those.
2, Having two set of 74HC595+ULN2803 and connecting both the end of coil to two IC legs so that one set will give positive and another set will give negative power to the same coil, in this case I will have to make sure the other lead of the coil goes to ground and it won't fry my IC.

Please quote your opinion on these thoughts.

Thanks,
Prabhu

 

[blambrec]

I'm just thinking that I might have been hasty in my drawing - 20V at the top and bottom should actually be the 50V from your ULN2803. A transistor with better power capabilities may be necessary. To address DIR would require an additional pin for every electromagnet you use, but that's it. Hopefully it's a little more clear.

As per your suggestions, I think they could both work. The trick for (1) might be finding a good switch to toggle between the coils - I would be interested to know what you find that's appropriate. In my opinion it would be more involved to put in two coils for every electromagnet instead of electrically switching the current flow, but I may be wrong.

(2) is not a bad idea, except you would need to be careful in how you implement it. What happens to the 2803 when it is not driving? If it becomes a ground then putting them to either side of the coil would probably work. Glancing at the datasheet however, it looks more like a Hi-Z/floating pin when not operating which makes things a little more interesting... If you can configure one to drive negative, then put them both at the same side and be sure to have some sort of a sufficient resistive load between them in case they were accidentally triggered simultaneously. I'm not sure that you have that flexibility to drive them this way though, in which case you're stuck with opposite ends of the coil. Since with opposite ends method you'll need a ground on either side, you will have to use switches to control access to the ground on either side. Once you simplify this circuit, you're back to my suggestion.

Hope this helps, and let me know if you have any questions.