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Data Logger Shield - SD card errors at 12+ volts
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Data Logger Shield - SD card errors at 12+ volts

by robertwynkoop on Wed Jan 16, 2019 2:37 pm

Hello,

Project seems to error when running on a stationary 12v solar power supply with a max voltage of 14.01 volts.

Project works at home on USB or 9v Vin power at the Mega.

Using a Mega, 808 Fona, and the Adafruit data logger.

Project is to take Vin Voltage readings every 15 mins, using voltage divider resistors. Every 4 hours it is to use the GSM shield to upload voltage readings.


Problems noticed:

- Only takes one reading and seems to lock up. I believe the SD interface fails. I only init SD at startup.
- Time date has reset to un-initialized once.

Any known issues running a combo like this with 14V Vin max.

Robert Wynkoop
Last edited by robertwynkoop on Thu Jan 17, 2019 11:25 am, edited 1 time in total.

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Re: Data Logger Shield - SD card errors at 12+ volts

by dastels on Thu Jan 17, 2019 10:44 am

My first thought is regarding the stability of the solar power. That it works at home with a stable power sully but not in the field makes me wonder if the solar power supply is dipping too low or is noisy. I doubt the 14v upper limit is a problem as the mega is rated to a max input of 20v.

Maybe the divider is draining too much current such that the supply browns out when the mega tries to do something beyond idling?

Without having more details, it sounds like a power issue to me.

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Re: Data Logger Shield - SD card errors at 12+ volts

by adafruit_support_bill on Thu Jan 17, 2019 11:16 am

- Only takes one reading and seems to look up. I believe the SD interface fails. I only init SD at startup.

Sounds like a power problem to me. SD writes will produce a peak in your current demand. And a supply voltage that is either too high or too low can be a problem. Are these issues happening when the solar conditions are near peak or on the low side?

I doubt the 14v upper limit is a problem as the mega is rated to a max input of 20v.

Not really. While it can tolerate 20v at the VIN pin without damage, the recommended supply voltage for operation is 7-12V. And even at 12v, it is relatively easy to overload the voltage regulator.

With a supply voltage of 14v, your regulator will be dissipating about 65% of your power as heat. An SD write can take 100mA or more - which translates to nearly a watt that your regulator needs to dissipate. And that is not counting the needs of the Mega, Fona and any other circuitry you have attached.

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Re: Data Logger Shield - SD card errors at 12+ volts

by robertwynkoop on Thu Jan 17, 2019 11:32 am

Testing with the solar system has normally been done on at 12+ - 13 volts. The logger has never been functional past the first sample, so I do not know how low of a voltage it will function.

I will test at home using a variable power supply I just bought.

I could run this using a 12 to 5v power supply from the inter webs, and instead of measuring Vin, provide an external input to measure battery voltage.

I will play around some more. I might also add a heart beat led blinker to show processing status.

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Please be positive and constructive with your questions and comments.