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Grogster

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Joined: 31/12/2012
Location: New Zealand
Posts: 9501

Posted: 04:36pm 21 Aug 2014

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As the Micromite manual states on page 17, these temp sensors are available cheaply on eBay, and I have found some nice encapsulated ones here.

The manual states that the sensor can work on parasitic power from the I/O pin, but I also assume I can run the sensor in the "Normal" way, with just the data line coming back to the I/O pin.

QUESTION: Do you still need the 4k7 pull-up resistor if you are using the more standard(non-parasitic) power?

EDIT: Manual says:

Quote
The DS18B20 can be powered separately by a 3V to 5V supply or it can operate on parasitic power from the Micromite as shown on the right. Multiple sensors can be used but a separate I/O pin and pullup resistor is required is required for each one.

That's fine, but does that mean you have to use separate pull-ups for each sensor only when used with parasitic power, or separate pull-ups no matter what?Edited by Grogster 2014-08-23

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WhiteWizzard
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Joined: 05/04/2013
Location: United Kingdom
Posts: 2927

Posted: 10:23pm 21 Aug 2014

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For each I/O pin used with a single DS18B20, you need a single pull-up on the I/O pin.

I would advise against using the one-wire search function to address multiple one-wire devices on a single I/O (via bit-banging). The OWSEARCH was dropped (and for good reason IMHO).

As the manual suggests, for multiple sensors, use a single sensor on it's own I/O pin and include one pull-up on that I/O.

If you need a large number of sensors then I would use a dedicated MM and then I2C the data to the main MM (I2C example given in manual App B). This way you could have upto 31 sensors on a 44-pinner and talk to a Master MicroMite with all the necessary data.

For sensors spaced further apart I would recommend a wireless link - currently working on a lower power version of that (but having a few 'teething' issues.

EDIT: And yes, you do need the resistor whether you are using parasitic power or normal power to the sensor.

WW
Edited by WhiteWizzard 2014-08-23

Grogster

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Posts: 9501

Posted: 10:47pm 21 Aug 2014

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Understood - thanks.

Smoke makes things work. When the smoke gets out, it stops!

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