lm75a from ebay

About a half year ago I bought some lm75a temperature sensors from eBay.

I placed two in a power supply, to measure the internal temperature on two positions, to switch a fan when the temperature passes a certain threshold.

Now it appears that the measured temperature is completely off.

They drift off a lot, to high values, but the strange thing is that the both keep in pace. Also when the fan switches on, the measured temperature of both sensors drops down.

But the measured temperature is much higher than the real temperature.

Does anybody have similar experience?

Is it a penalty for buying components on ebay?

Any comments are welcome.

thanks,

Gerrit.

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vsluiter over 10 years ago

Hi Gerrit,

John's answer might be a good point to look at, but your own idea is worth investigating too. You could consider buying one or two sensors through Farnell (although for private use you'd have to go > EUR 50) to verify the sensors.
Otherwise, buying a logic analyser to see whether your I²C decoding works could be worthwile too. Depending on your budget you could buy either a bus pirate ($25 on ebay) or a *recommended by me* Saleae logic. From your name I guess you have Dutch connections, in The Netherlands you can buy the Saleae Logic from Antratek.
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vsluiter over 10 years ago

Hi Gerrit,

John's answer might be a good point to look at, but your own idea is worth investigating too. You could consider buying one or two sensors through Farnell (although for private use you'd have to go > EUR 50) to verify the sensors.
Otherwise, buying a logic analyser to see whether your I²C decoding works could be worthwile too. Depending on your budget you could buy either a bus pirate ($25 on ebay) or a *recommended by me* Saleae logic. From your name I guess you have Dutch connections, in The Netherlands you can buy the Saleae Logic from Antratek.
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