. The photodiode will be collecting light from the LED (signal) and other sources like the sun, room lights, laptop screen, etc. (background). We can set the frequency of the LED signal (how rapidly it flashes) higher than these sources and then filter out the background frequencies. The sun provides DC light and light bulbs generally operate at 60 Hz or 120 Hz (50 or 100 Hz in some countries). Therefore, we should use frequencies above these values. Our choices are constrained at the high end as well. What is the maximum frequency we should operate the LED at to get a good signal at the photodiode

Fft review: linspace, fs, fftshift, nfft 1. generate one second of a cosine of w,-10hz sampled at f, = 100hz and assign it to x. define a tt as your time axis 2. take 64 points fft. 3. as you remember, the dft (which the fft implements) computes n samples of s2t where k-0,1,2, n -1. plot the magnitude of this 64-points fft at range 0 to 63, what do you think of this graph? 4â·to get the x-axis into a hz-frequency form, plot this 64-points fft between-50 to 50 (the 100hz sampling rate) and have n-points between them. 5. according to your figure, what frequency is this cosine wave at? 6. remember that the fft is evaluating from 0 to 2ď€. we are used to viewing graphs from-ď€ to ď€. therefore, you need to shift your graph. 7. now according to your shifted graph. what frequency is this at? 8. note that the spikes have long drop-offs? try a 1024-point dft. note that the peak is closer to 10 and the drop-off is quicker. although, now sidelobes are an issue

If gases like carbon dioxide and methane make up less than 1% of the total atmosphere, why is it important for scientists to monitor changes in percentages of these gases?

Why do astronauts in the space shuttle weigh less?