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.

 

Welcome to AAC!

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

 

Hi dl324,
My bus is so old that that is no problem

 

Hi dl324,
My bus is so old that that is no problem

If you drive on public roads, it could be.

 

I know. Thanks for your concern.

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

Thanks again!

 

Since the irf9540 is rated for 15A, it should be more than adequate to drive your bulbs.

 

Since the irf9540 is rated for 15A, it should be more than adequate to drive your bulbs.

Thanks! That is exactly the answer I needed.

 

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?

 

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?

They will be used as turn-signal.
But they are all extra lights.

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

 

They will be used as turn-signal.

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 was thinking a brake override circuit that would display brake signal instead of turn when brakes applied.

 

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!!

 

You want an XOR function.
I'll try to post a circuit in a couple hours.

 

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.



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

 

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

 

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.

 

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.

 

Note that R3 is just the simulated load and is not added to the actual circuit.

 

Note that R3 is just the simulated load and is not added to the actual circuit.

Yes, thanks, I realised that after a while of looking

I managed to locate a store with the following components: (Attached screenshot). Could you check if this is what was needed?

Thanks again for all the help!

 

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.