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INSTRUCTIONS: BUILD A KEYCHAIN RFID DETECTOR
Build your own RFID keychain detector that will buzz when a RFID reader is within range and scanning the airwaves for data.
Schematics and Parts:
Check out the schematics for the Zapped! keychain circuit board.
The core of our detector is based on an idea presented in the circuit described at:
http://margo.student.utwente.nl/el/radio-hf/rf-vibe/
The keychain we have used is a DAC Technologies model KAL-201 "Key Alert," (see photo at right) available from Fry's and outpost.com. Some advantages of this device are that it is cheap, it has a button with momentary switch, there is an opening on the side that can be used to access the sensitivity adjustment potentiometer and it comes with a small 12V battery.
Parts List:
| Part ID | Type | Value |
| R1 | Resistor | 3.3K |
| R2 | Resistor | 100K |
| R3 | Resistor | 1K |
| R4 | Resistor | 1.0M |
| R5 | Resistor | 10K |
| R6 | Potentiometer | 10K |
| R7 | Resistor | 3.3K |
| C1 | Capacitor | 18 to 27pF ok |
| C2 | Trimmer
Capacitor | 15-70pF |
| C3 | Capacitor | 10pF |
| C4 | Capacitor | 0.01µF |
| C5 | Capacitor | 0.01µF |
| C6 | Capacitor | 0.01µF |
| Q1 | Transistor | NPN, 2N5770 (or slightly lower sensitivity with 2N3904) |
| Q2 | Transistor | PNP, 2N3906 |
| IC1 | Op Amp | LM741 |
| SG1 | Buzzer | 12VDC, e.g. radio shack part #273-074 |
| S1 | Switch | Can be any type. Used as SPST. |
| G1 | Battery | 12V |
| L1 | Antenna | 17 turns of 24awg copper wire around the ferrite core from radio shack part #273-102 choke |
Now, let's start building the keychain detector! |
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 Zapped! Keychain before
 Zapped! Keychain before, inside
 Zapped! Keychain after, inside
 Zapped! Keychain after, front
 Zapped! Keychain after, backside
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