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No question is stupid. The idea is to be able to see the blinks. If the crystal is too fast, the blinks will be too fast to see-- it will appear as steady on. At very fast crystal, you might notice a difference in brightness of the different LEDs, but I'm unsure without trying.
A very simple proximity detector
DIY Infrared Proximity Sensor (Arduino Compatible)
Pocket Distance Scanner
Micromouse(mobile robot) IR distance sensor board +tips
Smart Distance Measuring Tape v2
Analog Output - Convert PWM to Voltage
IR-Distance (Analog Value) Sensor 2$
Extreme Surface Mount Soldering
interfacing u.fl connectors
Easy to Build Desk Top 3 Axis CNC Milling Machine