TMP36 Sensor Reads Incorrectly when Arduino Powered by 12V

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Genie123
 
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TMP36 Sensor Reads Incorrectly when Arduino Powered by 12V

Post by Genie123 »

Hello,

Currently I have an Arduino Uno hooked up to a TMP36 temperature sensor - to GND and 5V. When the Arduino is powered by the USB cable only, the output of the sensor is correct (around 0.75V as measured by multimeter) and its behavior seems to be normal. I then insert a barrel jack (USB to 2.1mm DC Booster Cable - 12V from Adafruit, being powered by a 5V 2A source) and the output from the TMP36 drops to about 0.5 -0.6V and fluctuates more than it did previously.

I believe the current provided from the USB booster barrel jack should be enough since in this same setup it allows me to power LEDs, read buttons, etc from the 5V pin. As well as the fact that for the TMP36, the "supply current runs well below 50 µA", according to the datasheet which is next to nothing. This phenomenon also occurs when the 3V3 pin is used in place of the 5V.

Any time the barrel jack is inserted this occurs (with or without USB cable). I have tested multiple TMP36 sensors as well as multiple Arduinos. The value I measure from the 5V pin is about 5.02V regardless of how it has been powered in this case.

Thank you in advance, any help is appreciated.

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adafruit_support_bill
 
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Re: TMP36 Sensor Reads Incorrectly when Arduino Powered by 1

Post by adafruit_support_bill »

I then insert a barrel jack (USB to 2.1mm DC Booster Cable - 12V from Adafruit, being powered by a 5V 2A source) and the output from the TMP36 drops to about 0.5 -0.6V and fluctuates more than it did previously.
The first question is: why would you do that? The Arduino runs on 5v. Boosting 5v to 12v so it can be re-regulated back to 5v (in a very inefficient manner) is asking for trouble.

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Genie123
 
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Re: TMP36 Sensor Reads Incorrectly when Arduino Powered by 1

Post by Genie123 »

I need the 12V to drive a 12V motor. I have considered stripping the end of the barrel jack and using that supply solely to power the motor, and have the Arduino powered by USB separately but this worked perfectly well for the most part that I didn't want to bother. You're right about the power inefficiencies, I am just stumped by all I can do with my current setup, yet it doesn't seem to function correctly with a TMP36.

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zener
 
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Re: TMP36 Sensor Reads Incorrectly when Arduino Powered by 1

Post by zener »

The booster might be noisy. Figure 24 on page 10 of the TMP36 datasheet shows a .1uF capacitor attached to the TMP36 and states this:
Note the 0.1 μF bypass capacitor on the input. This capacitor
should be a ceramic type, have very short leads (surface-mount
is preferable), and be located as close as possible in physical
proximity to the temperature sensor supply pin. Because these
temperature sensors operate on very little supply current and
may be exposed to very hostile electrical environments, it is
important to minimize the effects of radio frequency interference
(RFI) on these devices. The effect of RFI on these temperature
sensors specifically and on analog ICs in general is manifested as
abnormal dc shifts in the output voltage due to the rectification
of the high frequency ambient noise by the IC. When the
devices are operated in the presence of high frequency radiated
or conducted noise, a large value tantalum capacitor (±2.2 μF)
placed across the 0.1 μF ceramic capacitor may offer additional
noise immunity.

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