Hi I'm trying to find a cheap solut

[zandbj]

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

http://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.

 

[IRstuff]

Are they close together? Other options might be IRDA or BLE.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[zandbj]

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

 

[zandbj]

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.

 

[IRstuff]

OK, then sure, transformer coupling was used for 10BASE-T ethernet

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[IRstuff]

I had originally not suggested ethernet because I thought the cost might be too high, and that it might be overkill. Nevertheless

http://www.ti.com/product/dp83848j

has a $0.80 in 1k quantity, so that's pretty close

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[MacGyverS2000]

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

 

[zandbj]

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?

 

[IRstuff]

http://www.ebay.com/itm/10PCS-TS612...818919?hash=item1e940bc7e7:g:kw8AAOSwX~dWqeYu

comes to less than $1/each

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[zandbj]

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!

 

[zappedagain]

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

Z