07-09-2014, 11:40
Step 5 - Reading and conversion Analog Digital, Facts and Considerations
At this point we already have a device on which we obtain a variation of voltage of 1 mV per 10W / m2 of solar radiation. We now need to make the reading of voltage variation and presentation of the results in the desired drive or be in W / m2.
Nevertheless there are other ways to read and display the data in case the device for MeteoCercal.info was intended to use an Arduino Nano using one of its analog digital converters (ADC) to do the reading. The ADC Arduinos thereof (such as most common Arduinos) have a 10 bit resolution is 1024 or steps. By default the reference voltage to the ADC is 5 volt, this means that when applying a specific voltage value at the ADC input, it is compared with the 5V reference and the result given on a scale of 1024 steps (meaning 0 through 1023 ).
Let us consider that the device ever built can produce in one Rsh maximum voltage drop of 160mV, corresponding to 1600 W / m2. Admittedly, for reasons explained earlier, we had considered our measurements as corresponding to a value of 1300W / m 2, but it is also true that the value of the theoretical maximum of Solar Radiation in fact is an average, and in our latitudes is often a pyranometer obtain peak values of around 1600W / m2, so we will consider this possibility, and set a maximum limit of our reading device 1600W / m2.
Let us now consider what is the maximum resolution of the reading we could expect: 5V / 1023 = 4,88mV, as each mv corresponds to 10W / m 2, as we would have maximum resolution 48,8W / m2. This resolution does not serve us!
Luckily Arduinos allow you to change the reference voltage for the ADC, and in the case of the Arduino Nano to have the possibility of using a reference voltage very stable, internally generated 1.1V.
Let us see then how would our maximum resolution, if we use instead of the 5V 1,1V: 1.1V / 1023 = 1.07, ie 10,7W / m2. Improved the resolution almost 4 times, however, this resolution does not serve us!
Possibly, that much has already concluded that, given the reduced amplitude of signals with which we are dealing, they could hardly be read directly by the ADC of an Arduino with an acceptable level of resolution. So how to solve this?
The solution passes through a linear amplification of the amplitude of the original signal, so that the maximum value of 160mV corresponds 1,1V, our reference value ADC. Proceeding this way, we obtain a significant increase in resolution (the contained is like exercise), resulting in 1,56W / m2, a value already quite acceptable for this project.
One of the simplest and most reliable ways to carry out the amplification of our original signal, an operational amplifier is used, however, their choice requires some important considerations as will be seen below.
Continued ... in the next topic.
At this point we already have a device on which we obtain a variation of voltage of 1 mV per 10W / m2 of solar radiation. We now need to make the reading of voltage variation and presentation of the results in the desired drive or be in W / m2.
Nevertheless there are other ways to read and display the data in case the device for MeteoCercal.info was intended to use an Arduino Nano using one of its analog digital converters (ADC) to do the reading. The ADC Arduinos thereof (such as most common Arduinos) have a 10 bit resolution is 1024 or steps. By default the reference voltage to the ADC is 5 volt, this means that when applying a specific voltage value at the ADC input, it is compared with the 5V reference and the result given on a scale of 1024 steps (meaning 0 through 1023 ).
Let us consider that the device ever built can produce in one Rsh maximum voltage drop of 160mV, corresponding to 1600 W / m2. Admittedly, for reasons explained earlier, we had considered our measurements as corresponding to a value of 1300W / m 2, but it is also true that the value of the theoretical maximum of Solar Radiation in fact is an average, and in our latitudes is often a pyranometer obtain peak values of around 1600W / m2, so we will consider this possibility, and set a maximum limit of our reading device 1600W / m2.
Let us now consider what is the maximum resolution of the reading we could expect: 5V / 1023 = 4,88mV, as each mv corresponds to 10W / m 2, as we would have maximum resolution 48,8W / m2. This resolution does not serve us!
Luckily Arduinos allow you to change the reference voltage for the ADC, and in the case of the Arduino Nano to have the possibility of using a reference voltage very stable, internally generated 1.1V.
Let us see then how would our maximum resolution, if we use instead of the 5V 1,1V: 1.1V / 1023 = 1.07, ie 10,7W / m2. Improved the resolution almost 4 times, however, this resolution does not serve us!
Possibly, that much has already concluded that, given the reduced amplitude of signals with which we are dealing, they could hardly be read directly by the ADC of an Arduino with an acceptable level of resolution. So how to solve this?
The solution passes through a linear amplification of the amplitude of the original signal, so that the maximum value of 160mV corresponds 1,1V, our reference value ADC. Proceeding this way, we obtain a significant increase in resolution (the contained is like exercise), resulting in 1,56W / m2, a value already quite acceptable for this project.
One of the simplest and most reliable ways to carry out the amplification of our original signal, an operational amplifier is used, however, their choice requires some important considerations as will be seen below.
Continued ... in the next topic.