GoForSmoke:
afremont:
michinyon:
Why would you need "another pin" to supply 5V to the sensors ?You'd need another wire, to use the 3 wire mode, but you could connect that third power supply wire to +5V in
all sorts of ways without using "another pin".Clearly I've missed it again. In parasite power mode, you don't supply power to the Vcc pin of the sensor, it is GROUNDED. The sensor gets its power from the DQ data line, but the 1mA supplied is not enough to power the device during a temperature conversion. The device requires 1.5mA and the 4.7k pullup is too big. Also, you can tell all the devices on the bus to start a temp conversion at the same time so that they overlap the long delay during the conversion (750mS for 12 bits). If you had 20 devices, then you'd need to supply 30mA to the DQ bus by bypassing the pullup in some fashion. At any rate, the Vcc pin isn't being connected to anything but ground when using parasite power mode.
EDIT: Please, I beg both of you to download this document and look at Figure 4 and Figure 5 if nothing else:
http://datasheets.maximintegrated.com/en/ds/DS18B20.pdf
Please.Arduino UNO pin can supply 40 mA at 5V without damage.
------* the mystical, magical Parasite mode, the only way that makes sense! ------*
Why do I want to read that document? You explained the same thing already but seem to have trouble that anyone else should think that running a power wire makes any sense. Okay, fine, there's a special big-deal parasite mode.. got the message and the junk mail, thank you.
As Uncle Frank used to say: Is that a real poncho or is that a Sears' poncho?
First off, you shouldn't make bogus statements like that. 40mA is that absolute maximum current allowed out any single pin and 200mA is for the entire device. You do not operate devices at their maximum spec, the datasheet even tells you so. At 20mA output, an i/o pin is only guaranteed to give you 4.1V with a 5V supply. What do you think happens at 40mA load on the pin? People that read datasheets already know this though.
As for the "junk mail" I'm not sure what you are talking about, I sure didn't send you any PM. But since you think the time I spent trying to get you to understand how it works wasn't worthwhile, I'll keep your smart remarks in mind next time you want some help.
Go ahead and exceed specs on your own designs, but please don't recommend that others do so as well.
As for reading the document, what is the problem? Why argue with me and make me explain it numerous times when you could have just looked at the picture and understood. My advice is to start reading the datasheets, at least before you start arguing with someone.
If you can't see the advantage of parasite power mode, then it's probably due to a lack of education.
*NOTICE: Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage
to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability.
One last question for you. Why is it ok to dedicate an i/o pin for a clock and even another i/o pin for a CS, but using one to comply with manufacturer recommendations is wasteful? The 1-wire bus uses neither a clock nor a chip selector.