Combining indicator signal with rear brake lights

Thread Starter

Bbouman

Joined May 6, 2019
10
hello,

I found a thread on this forum with a circuit which I think could work for my old vw bus to use the rear brake lights as indicator lights that also keep blinking when using the brake. (I would then need one for every rear light)

I just wondered if the circuit needs adjustment to work with old fashioned brake lights (12V 21W) instead of led lights.

Would anyone be able to shed some light on this?

Thanks!

I think this circuit should work OK instead of a relay.
View attachment 119844
I have assumed that the battery is 12 volts.

Les.
A55D4A41-BFDC-468E-B101-9F596B1F66F6.png
 

dl324

Joined Mar 30, 2015
8,896
Welcome to AAC!

What is your location? In some locales, the change you're contemplating could be illegal.
 

Thread Starter

Bbouman

Joined May 6, 2019
10
I know. Thanks for your concern.

Any suggestions on the circuit for regular light bulbs would be appreciated.

Thanks again!
 

crutschow

Joined Mar 14, 2008
23,335
If the brake lights aren't being used as a turn-signal, why do you want them to blink in opposite phase with the turn-signal when the brakes are applied? :confused:
 

Thread Starter

Bbouman

Joined May 6, 2019
10
If the brake lights aren't being used as a turn-signal, why do you want them to blink in opposite phase with the turn-signal when the brakes are applied? :confused:
They will be used as turn-signal.
But they are all extra lights.

The bus originally has semaphores and only one central brake light.
 

SamR

Joined Mar 19, 2019
1,151
I was thinking a brake override circuit that would display brake signal instead of turn when brakes applied.
 

Thread Starter

Bbouman

Joined May 6, 2019
10
But only when the brake is applied...

Would you want a circuit that would operate the lamp with either the brakes and/or the turn signal?
I would like the indicator to work when the brake is applied and when it is not applied.

I thought the easiest would be to have the input from brake and from the indicator(after the flasher unit) as inputs. If one of the two inputs gives electricity it should give an output.
If both inputs give electricity it should give no output.

Like that it would let the indicator signal go through when there is no brake applied.
And the brake signal when there is no indicator signal.

When the brake would be applied together with the blinking indicator signal it then blocks the output every time the indicator blinks on (so reversing the on-off pattern).


Not sure if this is a clear explanation due to my limited knowledge of the right terms (and proper English)

Thanks for your help!!
 

crutschow

Joined Mar 14, 2008
23,335
You want an XOR function.
I'll try to post a circuit in a couple hours.
 
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crutschow

Joined Mar 14, 2008
23,335
Okay, here's the LTspice simulation of an XOR circuit using a couple diodes, a P-MOSFET, and a couple resistors.
The MOSFET must be a logic-level type (Vgs(thrs) ≤2V max).
As you can see, the output is ON only when either the brakes, or turn-signal are on.

upload_2019-5-10_20-20-37.png

It can also be done with a CMOS CD4077 XNOR gate and a P-MOSFET.
 
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Thread Starter

Bbouman

Joined May 6, 2019
10
Okay, here's the LTspice simulation of a XOR circuit using a couple diodes, a P-MOSFET, and a couple resistors.
The MOSFET must be a logic-level type (Vgs(thrs) ≤2V max).
As you can see, the output is ON only when either the brakes, or turn-signal are on.

View attachment 177080


It can also be done with a CMOS CD4077 XNOR gate and a P-MOSFET.
Perfect, this is exactly what I meant!
Thanks so much for all the help!!
I am such a noob at this subject..

I will try to get the parts and glue it together.
These part numbers all all a mystery to me but nothing a bit of google can’t overcome :)
 

crutschow

Joined Mar 14, 2008
23,335
These part numbers all all a mystery to me
They are not critical.
The diodes should be Schottky types, with a current rating of at least 3A, and a voltage rating of at least 60V.
The P-MOSFET should be a logic-level type (Vds(thres) ≥2V max.) with a current rating of at least 10A and a voltage rating of at least 60V.
 

Thread Starter

Bbouman

Joined May 6, 2019
10
They are not critical.
The diodes should be Schottky types, with a current rating of at least 3A, and a voltage rating of at least 60V.
The P-MOSFET should be a logic-level type (Vds(thres) ≥2V max.) with a current rating of at least 10A and a voltage rating of at least 60V.
Thanks for the extra guidance. That helps me a lot. I will let you know as soon as I have it assembled.
 

crutschow

Joined Mar 14, 2008
23,335
I managed to locate a store with the following components: (Attached screenshot). Could you check if this is what was needed?
The MOSFET is fine, but I prefer at least a 60V device for the diodes in an automotive environment.

For your interest, below is a different circuit for the same function (write-up here).
It uses four P-MOSFETs instead of the 3 diodes and one P-MOSFET.
The advantage is that the output can handle a higher current without the forward drop of the diode.
The main disadvantage is that the parts are likely more expensive.

upload_2019-5-14_13-26-0.png
 
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