Circuit Reverse Engineering - Different LED Resistor Values

Status
Not open for further replies.
D

dvm

New Member
I've got a simple circuit I am looking to reverse engineer to suit a slightly modified use case for my car steering wheel controls. I am only working on the 4 LED (assumed) lights at present as this is basically a separate circuit on the board to the main functionality.

The blue markup in the images is ground, the red is 12v from the car electrical system.

The measured resistor values are as below:
202 = 1.99k
272 = 2.705k
242 = 2.396k
182 = 1.806k

Question:
What I do not understand is why the resistor values differ for each LED ? I will be removing these LED's to use on my own custom made board.


 
Sort by date Sort by votes
Lightium said:
It's because the voltages and current before each LED are different.
Click to expand...
Thanks for the fast reply !! So I'm struggling to understand why this would be in that case ... I assume if I place the same values in front of each of them in the new design I may get differing brightness ?
 
Upvote 0 Downvote
I've just put a 13.8V supply onto the board and all of the LED's (by eye) look to be of the same brightness. Measured the voltages each side of the resistor connected to each LED and noted the below ... hopefully this is helpful.
 
Upvote 0 Downvote
Determine the specifications of each LED, such as forward voltage (Vf) and forward current (If). This information is typically available from the datasheet or can be measured using a multimeter.

Calculate Resistor Value for Each LED, To calculate the resistor value for each LED, you can use Ohm's law (V = I * R). The formula for calculating the resistor value is:
Resistor Value (R) = (Supply Voltage - LED Forward Voltage) / LED Forward Current
The supply voltage is the voltage across the LED circuit (usually the voltage of the power source, like a battery or power supply).
 
Upvote 0 Downvote
The difference between the resistors is small. The LED with the most current will be taking about 1.5 times as much current as the one that takes the least current. All the LEDs illuminate at the same time. I think that they resistor values have been adjusted to make the illumination level as even as possible.
 
Upvote 0 Downvote
I'd guess compensation for slightly different optics, window thickness or angle etc?
As others say, It's probably not enough variation to notice in use, without careful examination.
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

D
  • Question
Simple Circuit Reverse Engineering (steering wheel radio controls)
Replies
2
Views
3K
dvm
D
  • Solved
Microcontroller-based resistor ladder for gas gauge
Replies
16
Views
4K
shokjok
S
  • Question
How to Create a 12V Breathing/Fading LED Circuit with My Current Components?
2
Replies
34
Views
5K
Audrey2026
A
A
Hall effect sensor circuit. I have a need to produce a simple liquid flow LED Display
Replies
5
Views
819
ZipZapOuch
T
  • Question
switch circuit
Replies
16
Views
3K
ZipZapOuch
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…