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Forum Index : Microcontroller and PC projects : Quick DS18B20 question....
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
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: 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? Smoke makes things work. When the smoke gets out, it stops! |
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| WhiteWizzard Guru  Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
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 For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
Understood - thanks.  Smoke makes things work. When the smoke gets out, it stops! |
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