DS1822 1-Wire thermometers Vdd

Sunflower

I planning to install several DS1822 1-Wire thermometers on extended outdoor wires. The data sheet says they use typical 1 ma active. May I use a resistor, say 1k, inline with DS1822 Vdd to protect the Stamp voltage regulator from possible shorts with ground?

Jon Williams

If you do that you will shorten the distance you can run to the thermometers. If you decide to use the inline, 220 ohms will be fine. Make sure you use CAT-5 cable for your project; this will give you the greatest cable run (should be able to do 100 feet if you keep everything [noparse][[/noparse]connections] very clean and tidy).

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Jon Williams
Applications Engineer, Parallax
Dallas, TX· USA

Bean

It doesn't matter how much current the device uses, it gets it's current from the pull-up resistor.

If you put a 1K in series with the stamp pin you may have trouble because the stamp will not be able to pull the data line to ground level. If you put the 1K on the other side of the pull-up then the ds1822 will not be able to pull the data line to ground level.

I would think a 220 ohm, would provide protection enough and not affect the levels to badly. If you are using a 4.7K as a pull-up then the stamp could pull the line to down to 0.22volts.

Bean.

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Bean

Great minds think alike.... Jon you beat me to the punch while I was typing...
Bean.

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Sofalogic

Gentlemen:

You both beat me to the punch. I couldn't remember my password and had to wait for the e-mail (Great support function by the way) to remind me. I had a similar problem and used the experimental mode. I am using a four wire shielded cable. I will use the cat-5
next time.

Sofa

Sunflower

Thanks all, great support!