Hello
I build a small sensor node with 4 analog inputs for soil moisture sensors (the Vh400 from vegetronics).
The sensor uses the electric imp 002 chip as uC and for WiFi connectivity.
I power the PCB with 12V from an external PSU.
On board I have a 3.3V dc-dc converter to power the electric imp.
I also have a 3.5V LDO - The VH400 moisture sensors need at least 3.5V in to work properly.
The Vh400 outputs 0-3V analog which I feed through up-amp buffers to analog-in pins on the imp.
The soil moisture sensors are connected with TRS (stereo jack) connectors.
However I have a problem. If i disconnect and reconnect power to the board, measurements change.
With the analog sensors connected and the board powered up it measures as it should, let's say the sensors measure:
Sensor 1: 26%
Sensor 2: 68%
Sensor 3: 68%
Sensor 4: 62%
(These are the right measurements checked with reference measurement equipment).
If I measure voltage on the 5V rail i read ~5,02V
If i then disconnect the 12V power and put it back in, i get different measurements, even thou I should get the same:
Sensor 1: 5%
Sensor 2: 46%
Sensor 3: 45%
Sensor 4: 42%
If I measure voltage on the 5V rail i read ~4,82V
And now the tricky part: If i disconnect and reconnect a sensor by pulling out the mini-jack connector and putting it back in, readings go back to being normal. Also voltage on the 5V rail reads 5,02V again.
I have a feeling it has to do with the 5V LDO somehow, but don't know.
With no sensors connected via the mini jack connectors there a low volume but high frequency pitch sound coming from the board.
Please see attached schematics, I really cannot figure out what the problem might be.
I build a small sensor node with 4 analog inputs for soil moisture sensors (the Vh400 from vegetronics).
The sensor uses the electric imp 002 chip as uC and for WiFi connectivity.
I power the PCB with 12V from an external PSU.
On board I have a 3.3V dc-dc converter to power the electric imp.
I also have a 3.5V LDO - The VH400 moisture sensors need at least 3.5V in to work properly.
The Vh400 outputs 0-3V analog which I feed through up-amp buffers to analog-in pins on the imp.
The soil moisture sensors are connected with TRS (stereo jack) connectors.
However I have a problem. If i disconnect and reconnect power to the board, measurements change.
With the analog sensors connected and the board powered up it measures as it should, let's say the sensors measure:
Sensor 1: 26%
Sensor 2: 68%
Sensor 3: 68%
Sensor 4: 62%
(These are the right measurements checked with reference measurement equipment).
If I measure voltage on the 5V rail i read ~5,02V
If i then disconnect the 12V power and put it back in, i get different measurements, even thou I should get the same:
Sensor 1: 5%
Sensor 2: 46%
Sensor 3: 45%
Sensor 4: 42%
If I measure voltage on the 5V rail i read ~4,82V
And now the tricky part: If i disconnect and reconnect a sensor by pulling out the mini-jack connector and putting it back in, readings go back to being normal. Also voltage on the 5V rail reads 5,02V again.
I have a feeling it has to do with the 5V LDO somehow, but don't know.
With no sensors connected via the mini jack connectors there a low volume but high frequency pitch sound coming from the board.
Please see attached schematics, I really cannot figure out what the problem might be.
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