Download Smart PV Panel Project Handoff Sensors Dear Future Smart PV

Smart PV Panel Project Handoff
Sensors
Dear Future Smart PV Panel Team,
Currently, the sensing system is in good shape. The three environment variables (light, temperature,
and panel voltage) all function as expected, and an interrupt can be driven to the Arduino at appropriate
times. The Arduino is also able to read the explicit value of each environment variable. There are still
some improvements that can be made, however. But a quick summary of the system first.
So the system is essentially 3 conditioning circuits (see schematics). They are each made up of 3 main
stages: the filter, the amplifier/shifter and the comparator. First, the signal is filtered so that no noise is
amplified. Right now, the circuits use a low pass filter for 10Hz (these signals change very slowly). This
can probably be adjusted to allow even a smaller frequency window to pass through. The next stage is
the amplify/shift stage. The light sensor, temperature sensor, and solar panel all output values in
different voltage ranges. The light actually outputs current, which corresponds to approximately 0240mV. The temperature sensor initially output voltage in a negative range, but after the original part
was damaged, a new temperature sensor was used. The circuits, however, were designed for use with
the TI LM35 temperature sensor. Finally, the panel used output 0-12V. All of these ranges needed to be
shifted and scaled to a 0-5V range to work with the Arduino’s analog inputs. Finally, the comparator
stage generates the interrupt for the Arduino. The comparators are implemented with hysteresis (see
Sensor Operation and Conditioning section on the Detailed Design page of the P14421 Edge site) to
avoid bouncing at the output when the input bounces The amount of hysteresis and the setpoint
around which the hysteresis is centered can be adjusted with the potentiometers. In addition to the
main sensor system. The panel temperature is monitored for feedback, and uses thermocouples and
the AD565 thermocouple amplifier to do so.
With that in mind, some improvements can be made.


With the new sensor, the initial amplify/shift stage can be removed, since the sensor already
operates in the range of the Arduino.
In places, a simple resistor was used to convert current into voltage. A transimpedance
amplifier would be more reliable, but isn’t absolutely necessary.
In addition to the improvements, some suggestions for further work are:

Examine the relationship between the light sensor output and how much power can be
produced to better determine the setpoint for this sensor
That’s about it for the sensor part of the system. Overall though, the PCB needs to be redone (the
thermocouple amps could be moved onto the main board, and the existing one can be made lesscluttered, etc.). The main piece of advice I have for this is to avoid Express PCB. Their prices are
enticing, but there are actually cheaper fabrication services, and the CAD tool that Express offers is too
rudimentary (there are no design rule checks or link-versus-schematic checks). Eagle CAD is a great
program which has excellent DRC and LVS checking tools. Additionally, OshPark (a PCB fabrication
service) will fabricate boards for $5/square inch, and you can upload Eagle project files directly to their
website (N.B. if you use OshPark, you MUST download their DRC file, and run it in Eagle. There are
plenty of tutorials online for how to do this).
One last bit of advice: START THINGS EARLY! You WILL have a lot going on with other classes, so don’t
waste time.
I’m sure you are smart enough to figure everything out on your own, but, if there are questions that you
can’t seem to answer through existing documentation, please feel free to email me. I will list my
personal email at the end of the letter.
Good luck, and have fun with the project!
-Sean Kitko
[email protected]