Author Options:

Interface RS232 to 12 Volt One Wire Answered

I am interested in a circuit to interface an RS232 to a special 12 volt ONE-WIRE circuit.  It is special because it is an controller used in industry.  So I have a MAX3232 to convert my Arduino to RS232 levels, but that will get me to 2 wires.  I need to be able to make that into a ONE-Wire at 12 volt levels (not 3-5 etc) .  I see the MAXIM circuit (attached) for converting to one-wire at lower levels, but can't find anything to utilize a 12 volt one-wire level.  Hope I am being clear and thanks for your assistance.


Hmm, none of this works, I'm blowing stuff up!. The two grounds do not like each other. I'm thinking optoisolators now. I think i got the parts spec'd out OK, can I get an opinion from someone who knows more than me?

12v optoisolators.png

I think the Diode should be reversed...like this?

one diode to controller.png

Would this work?

one diode to controller.png

If you want help for a special 12V one wire interface, it would help if you specify WHICH special 12V one wire interface. Give the specification, some application notes, name the industry standard.

btw: there is circuit diagram attached.

Well, I thought I added an image....now not here. I'll try again. The problem that I have is this may or may not be a standard 'special' one wire interface. It is not documented and may be a trade secret, I was able to hack the protocol by listening to the traffic using my PC's serial port RX. The one wire data line is held high @12V unless there is data on the line. So I am ready with my MAX3232 and see the circuit which I will attempt to 'add image' again here, but again that circuit assumes a level of beteeen 3-5 volts and not 12. Can I simply use a diode to keep the TX from feeding back into the Rx? (Ill try again to add that circuit, but here is the URL that contains the circuit that uses 2N7002 's and some resistors) http://www.maximintegrated.com/en/app-notes/index.mvp/id/214

one wire to max3232.png

First: Are you sure that this 12V one wire uses the Maxim 1-Wire protocol? Normally, Maxim 1-Wire uses 5.5V max.

If it is this protocol, just with 12V, you can uses the schematic you posted instead of the MAX232. Set Vpullup to 12V and connect RxD with a voltage divider (two resistors) to bring the voltage down from 12V to 5V. Maybe, you need inverters in the TxD and Rxd lines - not sure here.

No I don't mean the trademarked (i'm guessing) 'One-Wire', I simply mean that it uses one wire. I already have a bunch of MAX3232's and I was hoping that this would add some added protection to my 3.3v uP board. So lets say I was really wanting to incorporate the MAX3232, what about simply putting a Diode in the transmit line and forget about pullup as the other end already is already pulled up to 12v. I will 'add image' of what this might look like.