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frequencies
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frequencies [2015/02/09 12:51] schultz [Frequency Selection] |
frequencies [2015/12/30 17:02] (current) schultz |
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| - | **Frequencies: 1111 1389 1724 2000 2273 2632 2941 3333 3571 3846** | + | **Frequencies: 1471, 1724, 2000, 2273, 2632, 2941, 3333, 3571, 3846, 4167** |
| ====== Frequency Selection ====== | ====== Frequency Selection ====== | ||
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| Creating the transmit signal and reading the receiver voltage require precise timing. Therefore, both of these tasks are accomplished using an interrupt service routine (ISR). In order to keep the processing to a reasonable amount both of these function are set on a 100 kHz maximum rate. | Creating the transmit signal and reading the receiver voltage require precise timing. Therefore, both of these tasks are accomplished using an interrupt service routine (ISR). In order to keep the processing to a reasonable amount both of these function are set on a 100 kHz maximum rate. | ||
| - | However, if the 10 bandpass filters with the associated power calculation and threshold computation are run at the 100 kHz maximum rate the computation will not be able to keep up with the data collection and the system will not be able to run real time. Therefore, the sample rate needs to be lower. | + | However, if the 10 bandpass filters with the associated power calculation and threshold computation are run at the 100 kHz maximum rate the computation will not be able to keep up with the data collection and the system will not be able to run real-time. Therefore, the sample rate needs to be lower. We are going to use a sample rate of SR=10 kHz. This means that the player frequencies need to be below 5 kHz. |
| - | We decided to use a sample rate of 10 kHz. This figure shows the signal collected when the receiver is pointed at the room lights. This signal is entirely noise. | + | The transmitter is creating the square waves by making an output pin high or low. The transition needs to be aligned to the 100 kHz timing clock. Therefore, there are a discrete set of allowable player frequencies. It takes two clock period to make a square wave. (One to turn a pin from low to high and one to turn it from high to low.) |
| - | {{ :noise_5k.jpg |}} | + | This plot shows the allowable square-wave frequencies. We want the frequencies that we use to be uniformly spread out over the frequency band (1 kHz - 5 kHz). We decide to use the frequencies of 1471, 1724, 2000, 2273, 2632, 2941, 3333, 3571, 3846, and 4167. These frequencies are shown on the plot as the red dots. |
| - | The good choice of player frequencies would be where the noise is low. However, the noise is spread over a lot of the spectrum. So it would be good to reduce the noise if possible. | + | {{:frequencies.jpg|}} |
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| - | The first step is to determine if the noise has the frequency components shown in the previous plot or if it is an aliased signal. This plot shows the same noise signal collected at sample rates of SR=500 kHz and SR=100 kHz. | + | |
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| - | {{ :noise_500k.jpg |}} | + | |
frequencies.1423511460.txt.gz · Last modified: 2015/02/09 12:51 by schultz
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