Feasibility and Advice on Car Dimmer Input and LED Driver

Thread Starter

jbragg77

Joined May 17, 2018
1
Hello,

I had a few specific questions as well as hoping to get overall feedback and advice. I am building an off-road capable camper and for my interior I wanted to add some red map light and under seat lighting to allow visibility in the cabin that preserves night vision. My general objectives are as follows:

1. Have an Arduino generate a PWM signal to feed two LED Drivers (Two Channels) to light the LEDs
2. Use the existing car dimmer circuit (a 12v PWM) as an input to the arduino such that when I dim my cabin lights, these new lights will also dim to an extent.
3. Use the Arduino to record rapid succession of turning these lights on and off such that within a short amount of time it will cycle through (Floor Lights Only, Floor Light - Map Light on Low, Floor Lights - Map Lights on High)
4. Given that I will make a PCB board for this project, make a few extra and sell to fellow enthusiast on a forum I frequent to recover some of the cost and help those guys achieve a similar effect.

For reference, here are the lights I will be driving:

9.5 Feet of LED red light strips (forum wont let me post the link) but about 22w at 12v

and two of these (Forum wont let me post the link) 2 pods containing 3 3w cree red lights

Also for handy reference here is the LED Driver spec sheet:
https://www.mouser.com/ds/2/256/MAX16819-MAX16820-84188.pdf

I have attached a diagram of the circuit I made for this purpose from Multisim.

My specific questions are:

1. I know that my battery voltage will be 13-16 volts depending on how it is charging at the moment, when I simulated this, I was under the impression that the bucking of the LED driver would clamp this down to 12 volts steady, and at constant amperage. This is not what I observed in multisim
A. Does this matter, are my leds going to look great and last a long time?
B. If not, how do I fix this

2. The Rsense resistor used to regulate everything is given both in the spec sheet, and the in the excel worksheet linked to in the spec sheet (the calculator). Those two sources don't agree, in the spreadsheet its telling me in a range of 3-6 amps of load, I will need a resistor between .04 to .20 ohms, tiny! even in the formula I calculate between 1 and 5 ohms.

A. am I way off, did I do something wrong?
B. how sensitive is all of this, as I want to put some pots on the final product so that other people that are using a very similiar setup (but maybe a little variance) can still use this solution.

3. I was going to simply read the pwm signal from my cars dimmer after voltage dividing it and reading it on the analog pin, any issue with doing this?

4. That dimmer connects to a an expensive 1200 dollar part on my truck, I have factored putting a .5amp fuse as well as a diode, is that enough protection to make sure my goofing around doesn't break something expensive?

5. Any and all general feedback, tips, or life lessons welcomed!
 

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kuzek

Joined May 29, 2018
4
LED dimming function implementation
LED driver circuit commonly used dimming methods can be divided into two types: analog dimming and PWM methods. Because the brightness of the LED is mainly affected by the forward current, it has a positive relationship with the forward current density. Both of the above dimming methods are through changing the flow
The average current of the LED changes its brightness.
Analog dimming: This method linearly regulates the current flowing through the LED in a continuous manner to change the brightness of the lamp and adjust the brightness of the LED over a wide range.
PWM dimming: by unit time
The LED current is turned on and off repeatedly to adjust the light emission brightness. The switching frequency is generally higher than 100 Hz so that this pulse current is not easily perceived by the human eye. The average current I flowing through the LED is linearly proportional to the duty cycle D.
The HX3143 is an LED constant current driver with a buck topology (Figure 1). The input voltage range is from 4 to 20V. The I LED is adjustable from 10mA to 1.2A. It can drive single or multiple LED strings. The LED current is equal to Current flowing through the inductor, the circuit with the VIN voltage increases, by monitoring the CS pin voltage to adjust the duty cycle of the LED, L, R2 current pulse so that the LED current is constant at the set value.
In fact, you can directly buy can be installed, no need to be so troublesome
 
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oz93666

Joined Sep 7, 2010
737
It's always good to underdrive led lights , I use strips a lot and they can run from 13 to 10 V ... but running high , will not give long life ... this may not be important in your situation since they may not get excessive use , but for domestic daily use I run below 12V
 
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