So I have one detection circuit with LED that flashes continuously when something is detected (1-2 sec interval). That's a bit nerving while it happens when you drive, especially at night.

I don't have any option to view or modify the code, so it would be nice if I can "hack" this LED to glow continuously....can I do it somehow with some active components?

Tnx in advance

I don't have any schematics of this thing. It is a Sensor device that detects when a car is in your "blind spot". So it blinks slowly when something comes in the zone, and rapidly if you put your turn light on....so that's basically a problem for a Cap while it will soften than all the impulses? right?

The LED is packed in a case where just two wires came out, so i need to look later onto the PCB to make it clear if it is with GND or Vcc regulated

And it is definitely a LED controlled with a micro controller

  • 2
    \$\begingroup\$ Without a schematic of the actual circuit, we can only make assumptions of how its made. Also, there are flashing LEDs which don't need electronics to make them flash. Not every flashing LED has a microcontroller behind it. In the old days we made LEDs flash with only a single UJT transistor, or 2 bipolars. Not everything needs a micro. \$\endgroup\$ – Bimpelrekkie Sep 12 '17 at 6:59
  • \$\begingroup\$ If it's a flashing LED (i.e. an LED with the flashing electronics embedded) just change it. Otherwise you might need to add a monostable (one or two BJTs, or an NE555). But we need the schematics, or at least we need to know how is this LED connected: anode tied to Vdd ? Cathode tied to gnd? If the flash is already produced using "old-style" electronics (e.g an astable), having the schematics would be even more useful (you could modify that circuit section). As a last resort, even putting a big capacitor in parallel to the LED might "soften" the flashes in something less annoying... \$\endgroup\$ – next-hack Sep 12 '17 at 7:16
  • \$\begingroup\$ @next-hack A parallel capacitor would have to be huge, and while it would charge slowly, the switching of the LED would happen relatively quickly when its voltage threshold is reached. \$\endgroup\$ – CL. Sep 12 '17 at 8:50
  • \$\begingroup\$ @CL. I know. That's why I wrote "big capacitor" and "as a last resort". \$\endgroup\$ – next-hack Sep 12 '17 at 11:11

In principle, this is a job for a retriggerable monostable (CD4047 or 74HC123).

To avoid voltage level problems with sensing the LED voltage, you could use a photocell to sense the flashes; this then drives the monostable with its period somewhat longer than the flash period, and that drives another LED which stays on as long as the flashes continue.



That's a bit nerving while it happens when you drive, especially at night.

Surely that is the whole point of the LED, to be visibly irritating enough that you notice it BEFORE you change lanes. Making it stay on you may never even notice it till it is too late.

It seems to me your real issue here is not the flashing but rather the fact that it is too bright at night. As such, I'd recommend you don't mess with the functionality, but rather switch in a resistor or add a pot that lets you adjust the brightness at night.

If you have the ability, there may also be the possibility of wiring up some circuit that adjusts the brightness based on the ambient light, or ties into the existing dashboard lighting levels.

  • \$\begingroup\$ Yeah, I know it make sense before you change the lane...while then the LED flashes more rapidlly, but when a car is in you blind spot, and you just drive straight forward, it flashes every 2 seconds....in my optionion, it would be better if it stays 1.8sec on, so that you know that this car is still there...that is iritating ;) \$\endgroup\$ – 159_v6 Sep 13 '17 at 10:15
  • \$\begingroup\$ It is a safety feature! Don't change it! \$\endgroup\$ – MatsK Sep 13 '17 at 11:39

Assuming you have access to a constant voltage somehere, something like this could work:


simulate this circuit – Schematic created using CircuitLab

Slow to turn off and probabaly overly complicated, but should work.


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