Project Feedback - Blinkers to positioning lights

Hi all,

First post here and very much beginner in electronics, trying to dive in.
For my motorcycle, I'm trying to implement positioning lights in the blinkers: When turning on the blinkers, the blinker blinks regularly. When the blinkers is turned off, after a short delay, the blinkers shine dimmed.

Below is the setup I have now; this setup is for either the front or the back of the bike, I'll eventually need 2 of these. This works fine if I attach 2 LED blinkers (draw about 0.15A each at 14V). The power comes from a 4S 18650 pack for approx 13.5 to 16.5 volts.

R1 and R2 form a voltage divider to feed the Attiny with a suitable voltage
R3 is read by Attiny to set the dimming
Attinys code handles debouncing, turning off all functionality when the regular blinker functionality is detected and uses one PWM to control the dimming (as defined by R3) for the positioning-lights functionality.

Any more info needed?


  1. when I attach 2 (or even 1) regular incandescent bulb (21W, 1.5A) instead of the LEDs something goes wrong and the whole circuit turns off. It seems the BMS of the battery kicks in since the measured voltage at the battery is only between 1 and 2 volts. I'd assume the IRLZ44N would easily handle the 1.5A drawn by a single bulb.
    Any insights why the circuit shuts down with a larger load?
  2. any feedback how to optimize, minimize or secure this setup?

(rest of data sheets deleted while only 2 links are allowed)

The IRLZ44N source and drain are reversed, the tiny 85 analog input will always be 5V.

The circuit is okay but your description isn’t. R2 is not a pull down resistor. If R2 wasn’t there, or too high a value, the attiny would be overvoltaged, destroying it.

R1 and R2 form a voltage divider. The voltage at the junction of two resistors is the input voltage * R2 / (R2+R1). As shown, 14 volts in should be approximately 3.8 volts out, depending upon the resistor tolerances.

To make the potentiometer function correctly, the outer two terminals connect to +5 and GND, respectively. The center pin, the wiper, is connected to the attiny analog input.

Thanks for noticing @JCA34F! Original post is corrected and updated!

Thanks for noticing and explaining @WhattsThat! Original post is corrected and updated!
Any clue why the whole system shuts down when the load is larger (1 incandescent bulb, 1.5A at 14V) The IRLZ44N should easily handle that load, no?

1 Like

Please do not go back and update posts, it makes the flow of the thread disjointed and of confusing reading to anyone trying to accomplish what your project does.
A fresh post each time makes the thread easier to comprehend.

Thank you for posting a good introduction with links, it makes offering advice that much easier. :+1: :+1:

Thanks.. Tom... :grinning: :+1: :coffee: :australia:

Thanks for sharing. It's really helpful.

fair enough! thanks for the feedback!

1 Like

I had assumed the mosfet connections were the source of difficulties, but since you said the problem persists, I re-read your original post and note your mention of a BMS.

Is the 14v battery shown a separate from the bike, li-ion pack? If so, what is the rating of the pack? Reason being that the 1.5 amp lamps can require significantly more current when cold. Halogen lights can require 10x the current at turn-on, when the lamp is cold. Tunsgen isn’t as bad but it still requires a much higher current when the filament is cold. A collapsing voltage is what you get when exceeding a batteries rating/capacity.

Thanks @WattsThat! That's good to know! I'm learning. I'm doing the circuit (obviously) away from the bike and I'm using a brand new 4S2P Li-Ion battery pack for that. I tried with an (older) 4S1P pack as well. The Li-Ion packs all have a BMS.
If the BMS kicks in, shouldn't it also kick in when I connect the bulb directly to the battery?
Would I be able to use a resistor to flatten the power peak?
What kind of resistor would be able to deal with those currents?
Any other idea how to handle that peak?

Thanks for the feedback, really appreciated!

Yes, it should. Does that happen?

1 Like


This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.