You have to connect the CA to +5, and NO, doing so will NOT "overvolt and damage them" - unless you don't use a resistor!When the LED is ON it's forward voltage is "3.5V"So, the balance of the 5V will be across the resistor - 1.5VThat 1.5V across the resistor will determine the LED current1.5V / 100? = 15mA
Get 100? (brown-black-brown) resistors - or my head will explode."How can I test that the resistors are working?"The only way to KNOW is with a voltmeter.+5 to CA, one lead of one resistor to any segment (cathode) with the other lead to Gnd.There will be approx 1.5V across that resistor.If the "spare" LED is a blue LED, you can use that.If the "spare" LED is another colour then it will have a different forward voltage and skew the results.
Power transfer involves maximizing the product of voltage and current in the load. When you do the maths it turns out the maximum transfer is when the output impedance of one device matches the input impedance of the other. However, here we do not want to transfer power but transfer voltage. To do this requires that the output impedance be very small compared to the input impedance. With an arduino the input impedance is very high and if you supply it from an output impedance of 10K then you get virtually perfect voltage transfer. The point about an impedance is that in most cases the value is frequency dependent so when quoting an impedance you should also specify the frequency where that impedance applies.
Hopefully this solves the issues I was having initially w/ the analog input voltage being skewed once plugged into my bike.