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Help with Dallas 1-wire circuit

makidoja

Nov 27, 2013
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Hi all

I'm trying to find out if the Dallas 1-wire system can be used with parasitic power of greater than 5vdc, what is the output of the 1-wire system? does it pulse the parasitic power or use a different method

If it pulses the parasitic power, could it be used to switch something like a mosfet to enable the parasitic power voltage to be increased to 12vdc?

Thanks

Mak
 

Fish4Fun

So long, and Thanks for all the Fish!
Aug 27, 2013
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makidoja.

I cannot imagine the scenario where one would WANT to use something other than the specified voltage range of 3.0Vdc to 5.5Vdc, you absolutely have to have a microcontroller to communicate with the device family, and I cannot think of any situation where one would have a microcontroller running @ more than 5Vdc.....

but that wasn't your question....I suppose you could devise a way of level shifting, but this would take any advantages of the device and throw them out the window, you might as well just go on and use a conventional RTD temperature probe and build the ADC section to be 12V compliant.

Fish
 

Arouse1973

Adam
Dec 18, 2013
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If you are talking about the dallas iButtons then their are two options supply a pull up of say 2K2 to the output., the device gets it's power from the resistor which charges up an internal capacitor. Or in parasitic mode the data from the micro charges up the internal capacitor which is what then powers the device. But you have to tell the iButton you are using this mode. The voltage range is 2.8V to 6V. But as stated by Fish you only comm with this device using a micro which as stated run on max 5V. So I don't really understand your question.
Adam
 

makidoja

Nov 27, 2013
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Update

Hi all

Sorry, let me explain more

Dallas do a I2C to 1 wire IC and a 8-channel, programmable I/O 1-Wire IC

I have a remote box with 8 relays that I would like to control with the 1 wire bus but the remote box which also has a RF pre-amp requires 12vdc for the relays and pre-amp.

So the idea is to have 12vdc which is switched low for the 1-wire data to be sent to the remote I/O chip in O mode only, which will control the relays and power the other sections of the remote board.

I estimate 12vdc at about 500ma should suffice.

The box also contains a RF-Preamp and rf will be sent back along the same cable.

I have already proven the RF and DC on the same coax (bit like a sat TV system power and RF is on the same coax) but I want to add the ability to control the 8 relays on the same coax cable.

Mak
 

Arouse1973

Adam
Dec 18, 2013
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Can you sketch something down and let us have a look. What are the names of the semiconductors you are planning to use.
Adam
 

Harald Kapp

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Nov 17, 2011
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So the idea is to have 12vdc which is switched low for the 1-wire data to be sent to the remote I/O chip in O mode only
regardless of the mode you use, you should never exceed the nominal operating voltage of the ICs.
You can generate the required 5V from the 12V supply using a linear regulator (I'd expect the current consumption to be rather low).
You can drive 12V relays from a 5V output of the IC using a simple relay driver circuit

Applying 12V to the ICs will destroy the chip with 99.99% probability.

Edit:
I just saw that this is more or less a continuation of this thread. You can use the output from the circuit I proposed there and generate:
1) a separate 5V supply from the 12V rail using a standard linear regulator.
2) use a voltage divider at the signal output of the circuit to generate the signal with 5V level. I recommend to add a Schmitt-Trigger gate (e.g. 2 gates from a 74HC14)between the signal output from the resistive divider and the Dallas chips to restore the signal quality.
 
Last edited:

OLIVE2222

Oct 2, 2011
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One wire should be OK, assuming you can find a way to use it in a 12V system.
But first being a data bus you can maybe think about a simpler solution for relay control like something based on 8 currents or voltage levels with comparators or µc to decode them . I remember an application like that for video camera selection and signal on the same coax.

Olivier
 
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