Hi. Please excuse me but I’m probably the dumbest person registered on this site. I’ve been lurking for years. Usually feel too stupid to ask the questions that I do have so I end up searching for hours, sometimes days to find what I need. Anyway here’s my question.
I have a motorcycle. The turn signal indicators on the gauge cluster are mounted very low and are very dim. Due to the way I have my phone mounted in the center of the bars, it blocks the turn indicator lights as well as the low fuel light etc.
So I created a small 3D printed enclosure and mounted three LEDs on top of the cluster. Installed 3 5v LED’s with I believe 220ohm resisters connected to the bike which is 12v.

Two LED’s for turn indicators and one for low fuel.

So they work great. During the day they are easy to see and mounted up high enough to avoid any obstructions. Great! I’m a genius!

So I took the bike out at night for the first time with these new LED’s and well they are so ridiculously bright that they light up the lane next me on the highway. Blind me and basically draw so much attention to me that it’s embarrassing.

So I need to be able to dim them at night.

Thinking back to my high school electronics class in the 1980’s my first thought was to install a photo resistor to increase resistance as it gets darker thus dimming the LED’s.

So before I start to try to figure out what I’ll need, I really want to know if this is even a viable solution? I could probably install a pot but I’d rather have them dim automatically if I can.

Am I headed in the right direction or is this, like many of my ideas, an idiotic solution that won’t work?

Thanks in advance!

 

Welcome to AAC!

The LDR has a dark resistance ~1MΩ and light resistance ~1kΩ so a bit much for using directly with LEDs. I'm sure some others here can give you guidance on a bit more sophisticated approach. Not knowing which LEDs you are using and their typical current needs we need a bit more information.

 

An LED has a datasheet that says its maximum allowed current, for most LEDs it is 30mA. You said your LEDs are 3.5V but the voltage has a range that might be as low as 3.2V.

The 12V battery is probably charging with 13.8V or more then the current in each LED is (13.8V - 3.2V)/220 ohms= 48.2mA which will soon burn out your LEDs.

The resistors heat with (13.8V - 3.2V) x 48.2mA= 0.51W which is too hot for each 1/2W resistor.

The small current in an LDR can turn down the current of a transistor when at night and the LDR can turn on full transistor current in daylight.

 

Welcome to AAC!

Am I headed in the right direction or is this, like many of my ideas, an idiotic solution that won’t work?

It's not idiotic, but probably more trouble than it's worth. Shorting a resistor or diode in series the diodes would be more straightforward.

How are these LEDs being activated? Is it like a car where you have a common ground and 12V is applied to the indicators when they're supposed to be on?

 

Easiest way to dim them would be with a PWM circuit. (Pulse Width Modulation) You can find some very simple PWM circuits using a 555 ic. You would have to experiment a bit with one of them to get an LDR to control it the way you want. Search for "555 PWM".

 

It's not an idiotic idea at all.

A Light Dependent Resistor (LDR) is good for sensing ambient light. On its own it will not work for your problem.

Start off with a 555-timer LED dimmer circuit. You can use this with manual control in order to manually adjust the LED brightness.

The next step if you wish automatic control is to add the LDR into the PWM control part of the circuit.

Edit: As zophas said before I posted.

 

A second series resistor to drop the LED current and brightness, and a single 3-pole relay to bypass the resistors when the lights are off. Unless you live where motorcycles must have headlights on at all times. And since the LED currents are quite low it can be a small relay with low contact current ratings.

 

Wow, thank you everyone for your replies. I’ve found a lot of PWM dimming circuit examples using 555 timers online, so that’s the approach I’m going to take, thanks to all of the great advice I received here. I really appreciate it!

 

Welcome to AAC!

It's not idiotic, but probably more trouble than it's worth. Shorting a resistor or diode in series the diodes would be more straightforward.

How are these LEDs being activated? Is it like a car where you have a common ground and 12V is applied to the indicators when they're supposed to be on?

Hi. Yes. That’s exactly how I wired them up. It’s probably not the best way but it’s the only way that I could think of at the time that I knew would work. Thank you!

 

It's not an idiotic idea at all.

A Light Dependent Resistor (LDR) is good for sensing ambient light. On its own it will not work for your problem.

Start off with a 555-timer LED dimmer circuit. You can use this with manual control in order to manually adjust the LED brightness.

The next step if you wish automatic control is to add the LDR into the PWM control part of the circuit.

Edit: As zophas said before I posted.

Thank You. This is exactly what I’m going to try.

 

Easiest way to dim them would be with a PWM circuit. (Pulse Width Modulation) You can find some very simple PWM circuits using a 555 ic. You would have to experiment a bit with one of them to get an LDR to control it the way you want. Search for "555 PWM".

Thank You. That search brought up a ton of results. I appreciate your help!

 

Thank You. That search brought up a ton of results. I appreciate your help!

No, the easiest way to dim them is with a series resistor that gets bypassed for bright during the daytime.. One resistor and one switch. THAT is as simple as it can get.

 

That search brought up a ton of results. I appreciate your help!

Depending on how you drive the LEDs, you could require 3 PWM circuits. Are you sure you want to incur that complexity when you can just reduce the voltage to the LEDs for low ambient light conditions with a switch (or 3)?

My phone adapts to ambient lighting when I'm using it as a GPS. It annoys me when it switches from night time to day time brightness when a street light shines on it, and then back.

 

@MisterBill2 does make a good point. Simplest solution would be a resistor (or three) and a switch. But I still think it would be more fun with a 555 PWM circuit. But that's just the tinkerer in me.

 

If you are proficient at constructing circuit assemblies that are rugged enough to last a few years riding on a motorcycle, and IF you are good enough at circuit design to discover how to use that system to dim three independent LEDs, and IF you get the duty cycle right the first time, THEN it might be fun.
And so, Z, how would you adjust the duty cycle of three independently driven LEDs?And where would the power feed for the 555 come from? And how would it switch from daytime to nigh time operation??

 

NE555 is 16V max so power is not a problem and using an LDR as a variable resistor in the timing circuit will take a bit of calculating but sounds like a project that just might be fun.

 

Well the bike does have a power source. So I would tinker around with some 555's and some LDR's and see what I could come up with. If the duty cycle is out a bit, too bad, it's not a Space Shuttle. If I ran into any serious problems I would ask on the AAC forum for some help.

 

Am I headed in the right direction or is this, like many of my ideas, an idiotic solution that won’t work?

It works:

 

That will work very well and dim the LEDs when a shadow blocks the sun for a moment.

 

That can work if the LEDs are controlled that way, with switching on the return to negative side. I was thinking that they were fed with a positive voltage from the function monitored. At least turn signal indicators are usually done that way in cars. My motorcycle of years past only had an ignition system, no lights.