Need help with my school project. -What value resistor to go in series with LED?

Thread Starter

asdf arfw

Joined Sep 9, 2017
43
http://tinyurl.com/y7pkf7gd
Here I designed my own measurement water level circuit.
The left hand-side which has open circuit wires is used to put in the water and let the water conduct a current.
But I'm wondering about my LED, Is it going to blow up if I only use 470 Ohm's resistor? Do you have any recommend for my circuit. Thanks for help.
 

Alec_t

Joined Sep 17, 2013
11,651
I'm wondering, does my LED gonna blow up if I only use 470 Ohm's resistor?
Check the datasheet for the particular LED you are using, to find the absolute maximum current (Imax) allowed.
The life of a LED will be greatly enhanced if you drive the LED at well below Imax.
Modern LEDs generally give an acceptable brightness with only a few mA.
 

dl324

Joined Mar 30, 2015
11,563
Edited circuit in question:
aacclip2.jpg
I'm wondering about my LED, Is it going to blow up if I only use 470 Ohm's resistor?
Assuming a forward voltage of 2V for the LEDs and 0.7V for the saturation voltage, the current would be approximately 5mA and should be safe for any LED.

Do you have any recommend for my circuit.
You may have problems with the electrodes when using a DC supply. Most circuits would use an AC voltage to avoid those problems.
 
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