Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Hi I'm trying to find a cheap solut

Hi I'm trying to find a cheap solut

Hi I'm trying to find a cheap solut

Hi I'm trying to find a cheap solution for a galvanic separated point to point RS485 bus. I need to send data between these 2 points in 1/2 duplex. There are full solutions for it like the www.linear.com/product/LTM2881 however these are very expensive and I would blow my complete budget on these babies.
There are some other standard solutions with opto couplers and a 2nd power supply however I don't like these either.
I came up with this idea (more or less based on the old appletalk or local talk as it was called I believe.) using 2 pulse transformers on both ends of the line.
I'm going to use manchester coding at a 100Kbits/sec data rate.
My question anybody any better ideas/suggestions?, any people having experience with this kind of set-up?, any advice type/model for the pulse transformers? my budget is max 2€ per point to point link on materials.
so including resistors, capacitors schottky diodes etc Excluding PCB, design costs etc.
All help/pointers welcome.

Thanks Jan Z.

RE: Hi I'm trying to find a cheap solut

Hi IRstuff no not really from aprox 2 meter up to 100 meter.. I'll have a look at the systems you mentioned. Thanks for your reply

RE: Hi I'm trying to find a cheap solut

Sorry took me a while to grasp the abbreviations no infrared and bluetooth isn't really an option. Really need to use good old copper. Also had a look at plastic fiber what might be a potential solution but is also too expensive and too fragile at the connector sides. Main use is machine building.

RE: Hi I'm trying to find a cheap solut

Depending upon quantity, your magnetics may blow your budget. Depending upon what mag you choose, you could be anywhere from $1 to $2/each. Choose wisely...

Dan - Owner

RE: Hi I'm trying to find a cheap solut

The ethernet idea would be a possibility however the chip is .80$ but also there is a 2 to 3$ pulse transformer used. (HX1198FNL). Also the ethernet is full duplex and I was thinking more like half duplex. I'll have a look if a re-design to full duplex would make sense. I'll also have a look at the 10base T standards and see if it helps me. Thanks for all the help so far I'll keep you posted.

PS. "Dan" don't what your link means I can't open it?

RE: Hi I'm trying to find a cheap solut

Look what I found! Link Galvanic seperation with capacitors! Now we are talking this would cost a standard driver chip and a few cents more.
But with a 10 lower frequency would mean a lot more phase difference and with capacitors on both sides of the cable would that mean doubling the capacitor size.....Wonder if it would work.... Food for thought All comments welcome!

RE: Hi I'm trying to find a cheap solut

Just make sure you read the Capacitor Selection (Clause 5) very carefully. How much potential are you attempting to isolate?


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close