My LM75 / DS75 Unit

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nwrightson
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My LM75 / DS75 Unit

 ·  Posted: 08.10.2009 - 00:16  ·  #1
Hi,

Here is the unit I developed for ready the LM75 or DS75 I2C Temperature interface IC's.

It handles the I2C or TWI Interface with multiple different levels of required accuracy.
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Re: My LM75 / DS75 Unit

 ·  Posted: 14.04.2010 - 13:27  ·  #2
Hello Neil,

the Unit's source is no longer in the new forum. Can you send it to me by PM or try to upload it once more?

Thank you, Michael

@rh:
PS: I suppose, this happened when the forum got updated.. I still get no Mail announcements, when I receive answers in 'my' threads. I deleted all my mails, as you suggested...
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Re: My LM75 / DS75 Unit

 ·  Posted: 15.04.2010 - 08:47  ·  #3
Hallo Michael,

ich dachte zwar ich hätte die Unit irgendwo gespeichert, aber ich finde sie nicht mehr. Evtl. hilft dir das aber weiter.

gruss
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Re: My LM75 / DS75 Unit

 ·  Posted: 15.04.2010 - 10:14  ·  #4
Hello Harry,

I had seen that link already - and I am using this way of communicating with the LM75. However, I find, that the LM75 has wide variations: I am running presently a series of 10 identical devices, each with one LM75 as internal temerature sensor and find the following:

  • 1 Some of the LM 75 have up to 2°C difference to the real temperature. That is in accordance with the data sheet.
  • 2 Some of the LM75 (in my case 3 of the 10) JUMP in the temperature readings from second to second for up to 5°C, i.e. they show 35°C, then 30.5°C and again 34.5°C.


I had been thinking, that I was having I²C bus problems, but there are more devices on the bus, that operate without problems (and yes: the pullups are installed !).
So, after some investigation, I came to the conclusion, that it is not the software, but rather a production variation of the LM75.

Anybody, who can confirm these observations??

Regards, Michael
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Re: My LM75 / DS75 Unit

 ·  Posted: 15.04.2010 - 14:00  ·  #5
Hallo Michael,

genau wegen diesen Temperatursprüngen hab ich mit den LM75 nichts mehr gemacht, hab aber inzwischen gehört, daß die Versorgungsspannung am LM75 sehr stabil sein muß. Ich bin leider noch nicht dazu gekommen weitere Tests zu machen, aber ich würde mal einen übertrieben großen Kondensator bei den Problem-ICs anlöten. Und es ist duchaus möglich, daß das nicht bei allen auftritt.

gruss
Harry
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Re: My LM75 / DS75 Unit

 ·  Posted: 15.04.2010 - 22:33  ·  #6
I hope that Neil doesn't have objections on me reposting his code...

Michael, take a note of Neil's remark:
Quote
This unit adds temperature monitoring facilities ustilising the DS75 I2C Interface IC's
The DS75 is a drop in replacement for the LM75 but it can also be programmed to give a
higher accuracy i.e. up to 12 Bit accuracy which is equal to a resolution of 0.0625C.
The LM75 is only good for 0.5 DegC accuracy.
This unit should also work with the LM75 but will only give the standard accuracy.
*** Note LM75 is only good for 100KHz data bus.

This might give you a hint what's going on if you use LM75 on 400kHz bus.
You must be logged in or your permissions are to low to see this Attachment(s).
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Re: My LM75 / DS75 Unit

 ·  Posted: 16.04.2010 - 07:54  ·  #7
Hello Avra,

thank you for the download. I will have a look at the DS75 and try also a local caps near to the device, as Harry suggested. However, I had tested the I²C wich 100 and 400 KBit/s each, and had no difference in behaviour. Then I swapped the Power supply unit of one device with good readings +/- 0.5°C with one with bad readings (+/- 2.5°C) and again: the bad one was still bad. So, I came to the conclusion, that the problem lies within the LM75 - although I can't imagine, that someone supplies a temp sensor with such a bad variety in readings. I do not think, that the problem is due to the hardware of the boards, they are full SMD, robot placed elements, industrial soldered, with LC-noise suppression etc...

I will investigate further and I will replace a bad LM75 with a DS75. I will keep in touch.

Thank you! Michael
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Re: My LM75 / DS75 Unit

 ·  Posted: 19.04.2010 - 06:02  ·  #8
Trying to add the file?
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