![the difference between fsk psk and ask the difference between fsk psk and ask](https://slidetodoc.com/presentation_image/33e715c8c04c1688dc7df7d5cdb8d10d/image-39.jpg)
We need to do an additional amount of processing to obtain the PSK though. The output of IC1A is FSK, as the site promises, but also works for ASK (at least for the values I have for the R’s, C’s, L’s, etc).
![the difference between fsk psk and ask the difference between fsk psk and ask](https://image.slidesharecdn.com/digitalmodulationtechniques-201106050907/85/digital-modulation-techniques-33-320.jpg)
You’ll notice this is basically the circuit from the DIY RFID page on the Arduino website.
![the difference between fsk psk and ask the difference between fsk psk and ask](https://i.ytimg.com/vi/zDteJJudhzk/hqdefault.jpg)
The Circuitīefore delving into how I decoded the data on my card, I’ll detail the circuit used to obtain the data. The pro-tip here is to be able to manually manipulate the data to troubleshoot, to figure out its structure, and to find a way of automating its future acquisition. Even better, I’ll build a minimal Arduino program and export the raw data into some program for manipulation (in my case, Matlab). Since I want to always use the smallest number of pieces when first investigating something, I’ll just gate each and send the result to the Arduino. Or I could just gate each low and high and send a high whenever this happens on two separate channels on the Arduino. Hurrah! But how do I actually feed that into a digital in on my Arduino? I could try to build a SR NOR Latch memory circuit and feed the 3.6V as the set switch and the (inverted) 0V as the reset switch. So I remember this site and near the bottom we have a description of how to interpret this.
![the difference between fsk psk and ask the difference between fsk psk and ask](https://i.imgur.com/Ub7Mx2Q.png)
So back to time space (rather than frequency space) and we see a voltage that primarily sits at some non-zero, non-high voltage (~2.5V) (due to the oscillations and the homemade RC filter), with quick peaks (~3.6V) and quick valleys (0V). As it shifts phase in either direction (by ), it extends the voltage by another half clock period… halving the frequency. What the? But this actually makes sense if it is PSK. Placing it into the field gives me a new peak at half the driving frequency. Ok, so now the major question is what my wanted tag does spectrally. Despite this I consider the FSK component of the project done). I placed one (an “uninteresting” tag) into the field and low and behold, peaks formed to the left and right of the main 125kHz frequency! This tag is obviously FSK (quick note: The program from the Arduino site picks up everything this tag has except the final encoding/protocol since the tag was not Manchester encoded. Sure enough, already existent peaks went up and down. I then tested the tag I already solved, the ASK tag, and watched the spectrum change. I put my oscilloscope into math mode, Fourier spectrum (or whatever they call it… spectrum analyzer?) and placed the probe onto the output of the last op amp. Ok, so the tag in question is NOT 13.56MHz! Back to 125kHz. Oh look, the capacitance of the system is so low that I may be getting parasitic capacitance from anything being brought near. It responded! But then again… so did a bag of chai tea. I did the BAD thing of building an entirely new LC resonator at 13.56MHz just to test the response of the tag in question. How does one even begin to determine unknown properties? Well, it wasn’t actually that difficult since I knew the theory behind the tag. So to start, I wanted to read a card whose properties were completely unknown. Alright! Determining the Modulation Scheme Interestingly, with some minor changes, it was able to do ASK demodulation in addition to the FSK. I decided to build the circuit from the Arduino website as I figured it would be more robust (it was). Furthermore, one of the websites I used ( here) had developed the same for FSK. I was able to previously develop a circuit and code for ASK. It is a lot so brace yourself! What’s Changedįirst, let’s back up. Well this was a pleasant surprise! I recently became obsessed with trying to figure out how PSK worked and was able to do so before the new year! But before I run off and learn even more, I need to dump all of my current information onto this blog.