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# Hi I'm trying to find a cheap solut

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## Hi I'm trying to find a cheap solut

(OP)
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

(OP)
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

(OP)
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
http://www.Hi-TecDesigns.com

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

(OP)
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

(OP)
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?

Z

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