Creating a simple DRL indicator sensitive circuit

Thread Starter

socast

Joined Feb 21, 2018
13
Hi there everyone,

I'm sure you're all tired of reading the line "I'm not very good with electronics but..." but I'm not very good with electronics and I'm hoping your expertise can help me.

So starting from the top,

I'm looking to wire some new day time running lights (DRLs) into my cars headlights. I will wire each headlight individually and keep all wiring/modifications within each headlight as there is an ignition live in the existing loom.
The DRL controllers on the market at the moment only have a single sensor wire. So with this in mind I will use a few basic components so the single sensor wire can switch the DRLs off/dim them when headlights are on (I still want them on when the sidelights are on) and to switch off the appropriate side when indicating (Hence treating each headlight individually with separate DRL controllers in each).

So by splicing the sensor wire into the headlight and indicator feeds I get the appropriate signals, however I have to fit a diode from the headlight to the sensor to prevent back flow and the same for the indicator. But this means that when using the indicator the DRL will flash in tandem with the indicator. The way I have (potentially) resolved this is by adding a capacitor. The cap will charge with the indicator pulse and provide a signal when the indicator is between flashes, at this point I will have to fit an additional diode between the cap and the indicator to stop reverse flow again.
Finally, as the sensor wire is just that, I need a way to drain the cap. So by adding an earth after the cap and before the diode that prevents back flow from the headlight, I can drain the cap. However to prevent the cap from instantly dumping all power via this new earth I need to fit a resistor to allow a controlled discharge. The cap and resistor will need to be fine tuned so that the DRL controller receives a constant signal while the indicator is on and then switches off roughly 1.5 seconds after the indicator has been stopped.

Below is a crude diagram I've drawn up, please excuse not using correct symbols etc. hopefully you will be able to read it and see what I'm trying to achieve.



The point at which I fall down is knowing which cap, diode and resistor to use... so nothing major


I've done no testing so far (switching point for the DRL controllers being a fairly important factor), and think that testing may well be my best route forward, but was hoping that someone on here may simply know off the top of their heads which components will suite my purposes.


So based on a 12v 2a pulse supplied to the indicator, I thought that using 1N5404 diodes, a 1uf 50v cap and a resistor rated at 20 Ohm

But I'm not really sure if my maths or even theory is correct, so any and all advice is greatly appreciated.
 

sghioto

Joined Dec 31, 2017
1,553
I think the below mod will work. The values for the cap and resistor will depend on the input resistance of the sensor line. But basically when the indicator light activates, the cap will charge immediately. It's the discharge of the cap that will hold the sensor line high between flashes. Do you have a link or model number of the DRL controller?
SG
EEE DLR lights.jpg
 

Thread Starter

socast

Joined Feb 21, 2018
13
Everything bar the DRL controllers has arrived, which after ordering I noticed won’t arrive until either the end of this month or the start of next
 

Thread Starter

socast

Joined Feb 21, 2018
13
First prototype made, I went with a 220uf cap and 33ohm resistor. That gives just over a second or so before the controller stops dipping the DRLs.

I’m intending to make another circuit to improve my design and also make it tidier.

80983DB0-5E17-4853-8E69-0A2C582AC54F.jpeg
 

sghioto

Joined Dec 31, 2017
1,553
Well from looking at the photo I can tell the 33 ohm resistor is wire between the cathode of the diodes and the + side of the cap. That's not how it's shown in the modified schematic in post #2. However it's actually OK because the cap is going to discharging through the sensor line on the DRL controller. Increasing the cap size will lengthen the delay time required. The resistor will have no effect on the delay time as wired so might as well stay at 33 ohms. Hope all this makes sense.
SG
 

Thread Starter

socast

Joined Feb 21, 2018
13
The black wire is the earth and the brown is the sensor wire (I’ll change this to yellow wire when I make the next circuit and buy some haha) the blue wires are the feeds from the headlight/indicator.
In your diagram the resistor goes from the sensor to earth, so to me looks to be doing nothing. Or should the resistor span both legs of the cap ?
 

sghioto

Joined Dec 31, 2017
1,553
In your diagram the resistor goes from the sensor to earth, so to me looks to be doing nothing.
That is correct in my drawing. The purpose of the resistor was to discharge cap. In this case because the resistance of the sensor line is fairly low the resistor is not needed. So just leave the resistor in the circuit as you have it wired. Below is the revised schematic.
SG
EEE DLR lights.jpg
 
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