DS18B20 temperature sensor - powering from Picaxe port

Paix

Senior Member
Something that I picked up from a comment by Hippy in the last couple of days. Powering the DS18B20 from a Picaxe output pin.

I am interested in in the concept of powering the sensor/s only at or about the time of reading, but do have a few questions.

I understand the max sink current to be 4mA and think that is during one-wire communication and the quiescent current is normally in the order of 1mA per sensor. So if running four sensors, the general saving is in the order of 4mA?

What is the required settling time between powering and reading the sensor.? I imagine that one second is more than sufficient, but am fairly curious about it. Should a pause be inserted after the READTEMP instruction and before powering down the power supply port pin, in the case of a single sensor arrangement?

In the case of multiple sensors, is there any significant advantage to be gained from powering each sensor from separate port pins, or is it just as well to power a number from the one port pin?

I'm thinking in terms of 08M2 and 18M2 chips and data logging with between four to ten (sets of) readings per hour (undecided). The short example shown uses the 08M2.

I don't think that I'm astute enough to really make a minimal power consumption device, but there is nothing like making the attempt, albeit in a piecemeal sort of fashion.

I haven't managed brevity either it seems . . . :)

DSconnection.jpg
 

Jeremy Harris

Senior Member
How much power do you want to save? The DS18B20 only seems to draw around 1uA max when in standby and not being interrogated. It hardly seems worth the bother of turning them on and off to me.

WRG to settling time, then I'd guess that it would be no more than a few mS, as the device is intended to be bus-powered when used in two, rather than three, wire mode, which means the first power the device would see would be the interrogation signal on the bus.
 

Paix

Senior Member
Thanks Jeremy, that does rather put it into context for me, on both the potential power saving and settling time questions.

I think spare Picaxe port pins can be put to much better use than trying to save a few microAmps. I'm always prepared to grasp at straws from time-to-time, unfortunately :)
 

Paix

Senior Member
Read it already Stan, thank you, sounds interesting and 70cm is easy due to being able to check it out with the station rig Icom IC7000.

I will be instrumenting a crown board in one, or more, of my beehives in the bottom of the garden. Probably an RS485 link, although I have four Inhaus RF-21400P transceiver modules to play with.

No Manuka honey here though. Out apiaries are 20 miles away. I guess your handle doesn't also indicate any connection with bees, but just the bushes?

De G0PAi
 

westaust55

Moderator
How much power do you want to save? The DS18B20 only seems to draw around 1uA max when in standby and not being interrogated. It hardly seems worth the bother of turning them on and off to me.

WRG to settling time, then I'd guess that it would be no more than a few mS, as the device is intended to be bus-powered when used in two, rather than three, wire mode, which means the first power the device would see would be the interrogation signal on the bus.
Have a read here also: http://www.picaxeforum.co.uk/showthread.php?11463
In particular post 19.
The DS18B20 in standby draws 750 nA typical or 1000 nA max (nA = nano Ampere)

Concur that it is hardly worth turning them off when in the idle/standby state
 

westaust55

Moderator
Isn't that EXACTLY what I wrote? (1000nA max = 1uA max)
Yes, that's why I concur'ed (I don't recall stating that I said anything like "it is not 1 uA")
I was quoting direct from the datasheet to confirm/agree with the "only seems to draw " statement.
 
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Jeremy Harris

Senior Member
Yes, that's why I concur'ed (I don't recall stating that I said anything like "it is not 1 uA")
I was quoting direct from the datasheet to confirm/agree with the "only seems to draw " statement.
OK, I misunderstood because you'd quoted my post, inferring it was in error, when in fact, like you, I'd taken the figure from the datasheet, hence my response.
 

manuka

Senior Member
Paix: Why "yes!" re manuka honey- I also kept bees for some years & at one stage had ~20 hives. However the site was far from ideal & honey yields, although significant (~50-100kg a hive p.a) were mostly a sweet pohutukawa. My intention was/is to take up the game again upon retirement & concentrate just on the esteemed manuka type. Aside from it's possible health benefits it's far & away THE tastiest going of course. Stan.
 

Paix

Senior Member
@Manuka; only 17 colonies at three out apiaries. your yields make me envious of course and it would be churlish of me not to agree with your verdict of Manuka being the tastiest honey there is - except mine of course. A triumph of PR if ever there was one and we could all do with taking a leaf out of that book be it UK honey or PICAXE chips.

March to October for three years now I have worked two days a week with a bee farmer and his 250+ colonies that are spread around, So I get more than a few looks into the boxes to be sure. Target 0.5 tonne plus for 2012. Carniolan and Buckfast strains.

Ian
 

papaof2

Senior Member
Several years ago, I was introduced to a small family bee operation with an eclectic mix of honey varieties - thistle honey, anyone? Although they still have an interesting mix of varieties, they no longer produce the thistle honey. I've tried several others (have Tupelo and at least two more in the pantry right now) but haven't found another that I like as well as the thistle.

John
 
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