I'm looking for a little bit of help on a project I'm working on.

I need to find some way to make led light bars (18w and 120w) to automatically start out dim and gradually brighten to full brightness over a few seconds when they get power and turn on.

They are activated by a infrared motion activated switch and ran off of a car battery. It's for night hunting lights and I need the function to keep from spooking animals when the green lights suddenly turn on. I've shot one wild hog with it, but I want to make it even better.

I need it to be waterproof simple and something I can integrate easily into my current build. Any ideas?

  • \$\begingroup\$ Isn't hunting at night illegal? I will not answer because I would rather the animals have a fair chance at survival. Hunting at night is not fair to the animals. Any ideas your ask? Yes buy your meat at the grocery store and or eat at a restaurant. \$\endgroup\$ – Misunderstood Feb 9 at 0:53
  • \$\begingroup\$ its for wild hog that is a major destructive invasive animal. they destroy farms and wild habitat eating food that native animals would otherwise eat. they also kill and eat deer fawn and bobcat kittens in the spring. when there are no more deer and your vegetables cost 6x more than they do now because wild hog destroy millions of acres of farmland a year you would wish more hunters like me would be willing to sit in a blind all night to hunt them. i don't tell you how to go about your traditions and i wouldn't expect you do the same. \$\endgroup\$ – txodm Feb 11 at 19:31
  • \$\begingroup\$ and no its not illegal to hunt invasive, exotic or none game species at night in Texas. \$\endgroup\$ – txodm Feb 11 at 19:33
  • \$\begingroup\$ I have been enlightened. am not a tree hugging vegan type. grew up in Wisconsin and hunting is a major sport. When I was 12 years old my parents would leave me home alone and I would shoot just about anything that moved. My biggest bitch about hunting was that hunting season was too cold. As I got older I concluded there are people I'd rather shoot than a deer. I got tinnitus at 12 years old shooting a 12 gauge one day. My ears started ringing very loudly and NEVER stopped. I lost 70% of my hearing and totally deaf at 3 kHz. Parents should not leave a 12 year old home alone with guns \$\endgroup\$ – Misunderstood Feb 11 at 19:40
  • \$\begingroup\$ that is understandable i got mu first 22 when i was 9 and my first 20 gauge shotgun when i was 11 or so. only difference was i was small and never liked shooting the shotgun because of the recoil. now it dosnt bother me. \$\endgroup\$ – txodm Feb 11 at 19:47

You need a circuit with a micro controller to adjust the intensity of lights as needed. As you have a IR, you can interface it to MC and adjust the intensity of the lights using Mosfet or Power electronic converter by varying the duty cycle of Mosfet or power electronic converter using (varying)PWM pulses from Microcontroller.

  • 1
    \$\begingroup\$ You don't NEED to use a micro, it is one way to go. \$\endgroup\$ – Misunderstood Feb 9 at 0:55

You have to measure the voltage drop of led strip

and you have to also check the current rating of the led strip

by ohm's law R=V/I

where V = supply voltage - voltage drop of led strip I = rated current of led strip

by calculating this you will get suitable resistance value for your led strip

by this resistance your led will glow with full brightness


you need to build the circuit that increase the resistance when you start the LED strip and comes to default resistance after some seconds

by this method current will low in starting time so led strip will glow dim and after some seconds it will glow to its full brightness

  • \$\begingroup\$ could i program a ATtiny85 chip to control a relay and switch between resistors? \$\endgroup\$ – txodm Feb 8 at 5:31
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    \$\begingroup\$ resistors to dim a 120w lamp? bad idea, use PWM or an SMPS with CC. \$\endgroup\$ – dandavis Feb 8 at 18:58

could i program a ATtiny85 chip to control a relay and switch between resistors?

An ATtiny would be perfect. You should use it to drive a CC chip like the TI LM3414. Very simple circuit with excellent efficiency. For a battery powered app you need all the efficiency you can get. I have been an EE for over 40 years and my current specialty is LED lighting efficiency.

You would probably be best off buying an eval board for $50 and modifying it for your project.

I know there are drivers with a soft start feature that may eliminate the need for the ATtiny. I don't know off the top of my head which drivers have this feature. I will look for it.

I may have some efficient strips that I can give you. For sure, I have some PCBs that you could populate with Samsung LM301Bs, the most efficient LEDs being made today with an efficacy of 218 lm/W at 4000K. All you need to build them is a $10 syringe of solder paste and a kitchen oven.

If you live near Gandbury TX we can go out and shoot hogs together.

  • \$\begingroup\$ man that would be awesome but im here in corpus so your about 5-6 hours from me lol i just ordered a Arduino Uno. Everyone has told me that would be the easiest way to program and control what ever i eventfully figure out. i was trying to find a dc-dc LED driver with a input for a PWM signal but i cant find any rated for the 120w, 10A of the big light bar and the ones i found are barely rated for the 18w, 1.5A of the small cubes. this is the most powerful one ive found. ledsupply.com/led-drivers/buckblock-dc-led-driver \$\endgroup\$ – txodm Feb 11 at 20:35
  • \$\begingroup\$ I had checked out the BuckBlock a couple of years ago. Not bad. You do not need high current. 350 mA is more than you want. At 350 mA LEDs get too hot. You do not want to have to use heatsinks and cooler is more efficient. You use a bunch of 100 mA mid power LEDs. At LEDSupply checkout the Mean Well LDH-45A-700 boost driver. $10! 90% efficiency and up to 64V. I design my strips to operate at about 45V with 48 LEDs in a 3P16S layout. Mean Well is the world leader in high reliability LED drivers, they ship millions every month with a good warranty, great price. \$\endgroup\$ – Misunderstood Feb 11 at 21:24
  • \$\begingroup\$ well the led light bar ive been using is 120w at 12v dc which should work out to 10A. it already has a heatsink built into the unit. my problem i im not sure if they have a built in driver or not. ive seen them taken apart and havent seen anything that looks like a driver of any kind. im wanting to use the LED light bars because they are already self contained and weatherproof. \$\endgroup\$ – txodm Feb 11 at 21:46
  • \$\begingroup\$ Save the enclosure. The LEDs are useless. They will drain your battery and generate too much more heat than radiant watts. If they actually draw 120 W, it only because the drivers are 25% efficient. The drivers are most likely resistors. I highly doubt they draw 120 watts. The resistors would be 75% efficient. The enclosure is the only thing that can be salvaged. My strips are 22" and 3.5" wide. The LEDs are 21¢ in qty for five strips and output about 65 lm each @ 100 mA. Whereas a top tier 3W Phillips Lumiled Luxeon Rebel ES with 220 lm @ 350 mA cost $1.40 each in the same qty. \$\endgroup\$ – Misunderstood Feb 11 at 22:21
  • \$\begingroup\$ would you happen to have a link to some green led strips that i can put in the housing and control with the arduino uno through a mosfet? and would this mosfet unit be good enough to use? amazon.com/gp/product/B077GPZZS6/ref=ask_ql_qh_dp_hza it shows as handling the current but dosent say if its a n channel \$\endgroup\$ – txodm Feb 11 at 22:24

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