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I’d love to dive straight forward into that project, as it seems to be a really cool feature.

Jaguar X-Type can be retrofitted with the stock puddle lights, mounted in doors. They are connected to the interior light and will stay on with it. They could be found on ebay at the price ~$15 each, but you’d need to find left and right versions and get the wiring. Also buying some spare door panel clamps would be a good idea. After all calculations and having seen them at work I have ditched that idea. There won’t be enough light and it’s not worth it. But I still want a puddle light feature in my car.

A year ago or so I have put 20cm LED light strips underneath the car body near to the front doors. The result is what you can see on the featured image. I just hooked them up to footwell light cables. Really love the dimming effect they make, can watch that forever. 🙂 But honestly… I’m not happy with the result. Firstly, because they are white and bright af and secondly, they stay lit up all the time, while the interior light is on and looks like an NFS parody.

But what if I could control each LED strip separately, preserving that dimming effect, but only when door opens?

I. Technical preps

Alright. Here we go then. Interior Lighting diagram:

Notes

  • Driver Door Ajar – IP6-22 (R)
  • Passenger Door Ajar – IP6-21 (R)
  • LH Rear Door Ajar – CA87-15 (Y)
  • RH Rear Door Ajar – CA86-18 (Y)

Logic

  • Sense front/rear & left/right door is open / closed
  • Light up / Turn off corresponding LED strip with dimming effect
  • Have an option to light up when the car is locking / unlocking
  • Easter eggs!

Tech part

  • 4 digital inputs to sense door states
  • 1 digital input to sense interior light / locking / unlocking
  • 4 PWM outputs to control LEDs
  • 4 MOSFETs to drive LEDs

Needed

  • MCU with 8 I/Os (4 PWMs + 4 digital) and 2K Flash memory
  • 4 x 2 pin connectors
  • 1 x 7 pin connector (2 pwr + 5 inputs)
  • 4 x LED strips (Yellow color)
  • 4 x waterproof automotive connectors

I will be building this device using Attiny24 MCU, but you can take any Arduino for this task.

Calculating wires and connectors…

Each LED strip I’m going to buy is consuming 330 mA at 12 V (maximum figures found in reviews). Seller says it should consume 6 Watts (6/12 = 0.5 A), probably that figure can vary depending on a color. Let’s add 20% to that and stick to 0.7 A to stay safe.

I will have to route wires from both sides of the car to the MCU installation point (near GEM). So the longest route will require approx. 3.5 meters (11,5 feet). 

According to the table below, found at https://www.powerstream.com/Wire_Size.htm, the lowest wire size appropriate for this task is 31 AWG (0.22606 mm). But the voltage drop at 0.5 A with this size of wire and 3.5 meters of length will be 0.748 V, leaving us with 11.252 V at the farthest LED. At the same time, the nearest LED with 1 meter (3 feet) of wire will get 11.805 V (0.195 V drop). This will result in uneven brightness and to eliminate it we can: a. Change the wire gauge to a thicker one with less conductance; b. Have same wire length for each LED. 

24 AWG will have a voltage drop of 0.039 V and 0.148 V at 1 and 3.5 m. So the difference should be not noticeable at all.

Calc I’ve used to find the voltage drop: https://www.waveformlighting.com/tech/led-strip-light-wire-gauge-calculator-requirements.

 

Connectors to use.

I would use thicker cables if I hadn’t need to push them through the rubber sills, which protect the interior. It was quite challenging last time, so I will try to get the smallest wire and the connectors. JST 2.0 PH series will be ok.

Part Pcs. Link
Attiny24 / Arduino
1
MOSFET IRFR1010Z
4
LED strip (yellow)
4
24 AWG cable (10m)
1
Heat shrink
n/a
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