Disable Brake Light while Turn Signal is On

Thread Starter

Marshall Law

Joined Feb 25, 2018
6
I would like to add additional brake and turn signals to a project vehicle. There will be 2 LED strips running along both sides of the vehicle. One RED LED strip, and One Amber/Yellow LED strip. (total of 4 Strips, 2 per side.) I taped into the rear brake & turn lamp wiring to include these new lights. I used custom T - Wire Harnesses to tap into the rear wiring, so I'm not able to access the turn signal wire before its sent through flasher relay in the vehicles fuse box. That wire is up under the dash, and I really don't want to tear the dash apart to access it. Nor did I want to splice into any of the original vehicles wiring. If needed here is the Park/Tail Light Wiring Diagram https://imgur.com/a/veBWp .. Currently they are just wired directly to the turn & brake wires of the vehicle, (I used the 3rd brake light wiring - to avoid the "Tail/Park lights" which include the rear brakes) so this results in the "Left Brake" strip powered, while the "Left Turn Signal" strip is flashing. Assuming you have your foot on the break, while the turn signal is on -- usually at a traffic light) I tried just using a 5-Pin relay (12v Bosch Style), with the Brake connected to NO, and the turn signal connected to NC, but this resulted in a light show of "Red and Yellow" alternating lights. I could have just switched this around, putting Brake on NC, and Turn on NO, but when you brake the turn signal would not flash.

What I would like to achieve is, when the Turn Signal is active for that side, then the brake light strip for that side is off completely (doesn't flash, doesn't receive power)


qR37pO1.png .
 

Thread Starter

Marshall Law

Joined Feb 25, 2018
6
Please note, that this doesn't change/effect the function of the stock lights. This is adding Additional lights, which would increase safety and visibility on the road.
 

crutschow

Joined Mar 14, 2008
24,929
What I would like to achieve is, when the Turn Signal is active for that side, then the brake light strip for that side is off completely (doesn't flash, doesn't receive power)
So, when the turn signal starts, the brake light strip in inhibited for the duration of the flashing and then comes back on perhaps a second or so after that.
Correct?

If so, you could use a P-MOSFET as a switch to the brake light strip as shown below.
The P=MOSFET can be just about any standard (not logic level) with a Vds rating of ≥50V and an ON-resistance of ≤ 0.1Ω.
You may have to adjust the value of R1 and/or C1 to get the turn back on delay you need.
Smaller values give a shorter delay.

upload_2018-2-26_0-43-15.png
 

Thread Starter

Marshall Law

Joined Feb 25, 2018
6
So, when the turn signal starts, the brake light strip in inhibited for the duration of the flashing and then comes back on perhaps a second or so after that.
Correct?

If so, you could use a P-MOSFET as a switch to the brake light strip as shown below.
The P=MOSFET can be just about any standard (not logic level) with a Vds rating of ≥50V and an ON-resistance of ≤ 0.1Ω.
You may have to adjust the value of R1 and/or C1 to get the turn back on delay you need.
Smaller values give a shorter delay.

View attachment 147023
When mapped out on http://tinyurl.com/y7y3q9zn that doesn't appear to function, did I miss something?
(attachment available for import into circuit simulator - "Import from Local File")
 

Attachments

crutschow

Joined Mar 14, 2008
24,929
When mapped out on http://tinyurl.com/y7y3q9zn that doesn't appear to function, did I miss something?
You missed that the turn signal switch output doesn't go to an open circuit, it has lamps providing a low impedance path to ground when the switch opens that allows the circuit to operate properly.
Also one end of the capacitor is floating.

For simulation purposes you can emulate the bulbs by adding a 1kΩ resistor to ground at the switch output.
 
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Thread Starter

Marshall Law

Joined Feb 25, 2018
6
You missed that the turn signal switch output doesn't go to an open circuit, it has lamps providing a low impedance path to ground when the switch opens that allows the circuit to operate properly.
Also one end of the capacitor is floating.

For simulation purposes you can emulate the bulbs by adding a 1kΩ resistor to ground at the switch output.
r

idk if that site is broke, but it doesn't appear to simulate correctly.. I'm not sure what you mean by output of switch doesn't go to open circuit.
http://tinyurl.com/yagsjmbd
In the vehicle, we are tapped into the 12v signal wire that's sent from the "Flasher" relay to the rear of the trunk before its passed to the bulb/lamb..

(Sorry Electrical is not my thing; more of the programmer/designer type)

Also tried this http://tinyurl.com/yalkagph
 
Last edited:

crutschow

Joined Mar 14, 2008
24,929
I'm not sure what you mean by output of switch doesn't go to open circuit.
I mean you have no load on the switch but my circuit, so the circuit is looking at a open circuit when the switch is open.
In real life the switch is connected to several bulbs that go to ground.
Those allow the circuit to work properly.

I said to add the 1k resistor to ground at the switch output.
You added it in series with the circuit, which has no effect.

In your second circuit you added a diode in series (why?) which also keeps the circuit from working.
If you don't know much about circuits then please don't try to change the design. :rolleyes:

Below is the LTspice simulation of the circuit.

upload_2018-2-26_20-27-2.png
 
Last edited:

eetech00

Joined Jun 8, 2013
1,894
Hi

You might be able to do something like this:

DisableBrakeLight.png

The capacitor would need to provide enough of a delay to span the off time of the flasher. This prevents the relay from dropping. When the flasher stops, the relay will drop out after a short delay (about 1/2 second).

eT
 

Thread Starter

Marshall Law

Joined Feb 25, 2018
6
I mean you have no load on the switch but my circuit, so the circuit is looking at a open circuit when the switch is open.
In real life the switch is connected to several bulbs that go to ground.
Those allow the circuit to work properly.

I said to add the 1k resistor to ground at the switch output.
You added it in series with the circuit, which has no effect.
I posted the wrong simulation link, sorry, I had it setup like the lamp in the 2nd link, but when it didn't work either I played around with by moving it to different places.

Only put a switch in the simulation so I could 'simulated' a blink. I was assuming, pushing the switch (on left) should interrupt power flow through the mosfet.

In your second circuit you added a diode in series (why?) which also keeps the circuit from working.
If you don't know much about circuits then please don't try to change the design. :rolleyes:
I was just trying different things, with or without the diode the simulation didn't work. I put the diode there because it simulated power flowing back from the capacitor to the 'lamp'
 

crutschow

Joined Mar 14, 2008
24,929
I put the diode there because it simulated power flowing back from the capacitor to the 'lamp'
A diode doesn't simulate power. It blocks current in one direction.
Only put a switch in the simulation so I could 'simulated' a blink. I was assuming, pushing the switch (on left) should interrupt power flow through the mosfet.
Yes.

I'm not familiar with the Falstad simulator so can't help you with that.
But it works in my LTspice simulation, as you can see.

So are you satisfied with the circuit now?
 

Thread Starter

Marshall Law

Joined Feb 25, 2018
6
A diode doesn't simulate power. It blocks current in one direction.

Without the Diode there, between the resistor and "turn signal" 12v, the power from the Capacitor is flowing back toward the "lamp."
I've been playing around with this circuit on my breadboard, and without the diode, the lamp (LED on my breadboard) is showing power on my volt meter..
 

crutschow

Joined Mar 14, 2008
24,929
Without the Diode there, between the resistor and "turn signal" 12v, the power from the Capacitor is flowing back toward the "lamp."
Which is the intention of the circuit design.
That small current has no adverse effect on the "lamp".
I've been playing around with this circuit on my breadboard, and without the diode, the lamp (LED on my breadboard) is showing power on my volt meter..
But the LED is not lighting, correct?
A LED does not properly represent the incandescent lamps in your vehicle since it has a couple volt forward drop, even at very low current.
Add a 1kΩ resistor to ground.
 
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