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| Sensing an RFID car key? |
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| iXod:
--- Quote from: mikeselectricstuff on August 31, 2019, 09:51:17 am ---You could probably do it using audio - the ear is very good at hearing patterns and changes - I'd suggest something like sweeping the carrier with maybe a 1khz sinewave, and feeding the detector to an audio amp and headphones. Use the key you have to optimise the sweep range and audio sensitivity. It may also be possible to just switch between 2 frequencies instead of sweeping. --- End quote --- Ignorant question: Doesn’t sweeping entail at least 2 frequencies? Sweeping a 125 KHz signal with 1 KHz, how is that done? Thanks. |
| mikeselectricstuff:
--- Quote from: iXod on August 31, 2019, 09:08:57 pm --- --- Quote from: mikeselectricstuff on August 31, 2019, 09:51:17 am ---You could probably do it using audio - the ear is very good at hearing patterns and changes - I'd suggest something like sweeping the carrier with maybe a 1khz sinewave, and feeding the detector to an audio amp and headphones. Use the key you have to optimise the sweep range and audio sensitivity. It may also be possible to just switch between 2 frequencies instead of sweeping. --- End quote --- Ignorant question: Doesn’t sweeping entail at least 2 frequencies? Sweeping a 125 KHz signal with 1 KHz, how is that done? Thanks. --- End quote --- Voltage controlled oscillator or synthesiser |
| iXod:
--- Quote from: mikeselectricstuff on September 01, 2019, 10:11:50 am --- --- Quote from: iXod on August 31, 2019, 09:08:57 pm ---Ignorant question: Doesn’t sweeping entail at least 2 frequencies? Sweeping a 125 KHz signal with 1 KHz, how is that done? --- End quote --- Voltage controlled oscillator or synthesiser --- End quote --- Hardware aside, the method you’re recommending is 125 KHz swept by 1 KHz to 1.5 KHz? Or...? Thanks. |
| Yansi:
The purpose of the frequency sweep is to be able to distinguish a general broadband signal attenuation and a "sharp" resonance dip at 125kHz. "sharp" because the loaded LC circuit in the transponder will not have very large Q, so a few kHz sweep is likely very small to have any effect. The sweep should be across at least a few tens of kHz. |
| iXod:
So if I AM modulate the 125 KHz by 1 KHz, sweeping from approximately 115 to 135 KHz, this will give an audio indication (a change in the 1 KHz tone) when the RFID circuit resonates? Please suggest corrections to the method and my understanding. Thanks. |
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