Have tried again, so any luck in seeing it?

 

Got the picture this time. The relay, resistors and capacitors make me wonder if the design is using an integrator/low pass filter to convert the pulsing 12V to a smoothed 6V (like SgtWookie's simulation). That stops the relay from pulsing from just the tail light signal and allows it to act as a voltage sensing device, i.e., it doesn't pull in at 6V, but does at 12V. The other 3 devices look like rectifiers/diodes. Do you have the part numbers for them?

John

BTW, I've had some odd problems posting images too recently.

 

sorry, no part numbers......

I think the 3 other devices are acting as load resistors - as you will need them for the LED light bar (since this is no longer going to light the bulb as a tail light), and LED Indictors in order to fool the computer not to bring up an error message - just not sure why there are 3 if that's the case....

That does sound a better idea, as then not too many components required - so how do I do that then.....

 

A quick search for voltage-controlled switch turned up this circuit:

(source: http://www.zen22142.zen.co.uk/Circuits/Switching/vcs555.htm)

A voltage divider at the input, if needed (2 resistors), could set the threshold higher than the usual 2/3 of the power supply (i.e., 8 V for 12V supply). Then the integrated pulse would not activate the relay, but the full 12 volts would.

John

Edit: As you can see, the 555-based circuit is similar to SgtWookie's. It just replaced the comparator. Unfortunately, the integrator SgttWookie drew will not pass much current to operate a relay directly.

 

cool, I can easy pick up a 555 timer from maplin, but what are the other parts in the diagram - sorry - newbie at these drawing with their technical icons etc but I do recognise the diode symbol tho

 

K1 is the relay that applies full voltage to the brake lamp. You could also use a mosfet as SgtWookie showed. C1 is a small capactor to stabilize the 555 (it may not be needed, but doesn't hurt to have it). Your input should be the diode, 2 resistors, and capacitor as shown in the other comparator-based circuit. You need some way to smooth the pulsing 12V to give the average voltage. That input circuit would replace R1 in the 555 diagram.

John

 

so is this right then??

If so, I just need to know the values of C1, C2 and R1 then are we good to go?

 

Here it is with SgtWookie's values plugged in.

If the pulsing voltage still activates, reduce R1 (it's effectively just a voltage divider with R2). If the brake does not activate the relay, reduce R2. Sorry about the different appearance of the 555, that's the only model I have in my program. Capacitances are in microfarads (uF). Note, you can also modify to use a mosfet instead of relay, but maybe the relay is best as a start.

John

 

ok, so on my shopping list, I need (per light):-

1x 12v Relay - does it matter what wattage they are as I have a 30W and 40W?

1x NE555N Timer

2x 12v 5W Zener Diodes

1x 2W Res 100K resistor

1x 2W Res 220K resistor

As for the capacitors......this is where I am unsure to their values as never used these before.......when I have looked at Maplin, they don't seem to do 12v versions - is this right?

 

ok, so on my shopping list, I need (per light):-

Why per ligt? Are they used for turn signals? Won't hurt, though, to have one per light and that will lessen the wattage carried per relay.

1x 12v Relay - does it matter what wattage they are as I have a 30W and 40W?

Depends on the DC rating at 12V. Need to know the wattage of your bulbs. Those values sound about right. Some generic automotive relays are quite cheap ~$5 to 7 USD.

1x NE555N Timer

Yes.

2x 12v 5W Zener Diodes

No. Those are ordinary diodes, like 1N4001 or 1N4002.

1x 2W Res 100K resistor
1x 2W Res 220K resistor

In this circuit, you do not need such high wattage. 1/4 watt will do. If Maplins is like the old Radio Shack, I would just get its assortment of 1/4 watt resistors.

As for the capacitors......this is where I am unsure to their values as never used these before.......when I have looked at Maplin, they don't seem to do 12v versions - is this right?

You do not need (or want) electrolytic capacitors in this circuit. Use regular polyester (Mylar) or ceramic . They will come in voltage ratings of 35V or more, which will be OK. Go for physical size, cost, and availability. Voltage rating, as long as it is high enough, doesn't matter.

John

 

When I said per light, I mean't per side, so one set up for the left and one for the right

For the Diodes - I have found both 1N4001 or 1N4002, so which one is best?

As for the resistors - I have found a pack of 1/4 watt - but then they are stated in ohms - so what ohm do I need?

For the Capacitors - I have found:
Poly Layer 0.1 and Poly Layer 0.01 - they don't have any voltage stated on them

Will get there in the end.......

 

Diodes: Go to the datasheet site I gave before. 1N4001 is rated at 50V; 1N4002 is 100V. Either will probably work, but if you have a choice, use the 1N4002.

Resistors: The "K" means 1000X, so 100K = 100,000 ohms, etc.

Capacitors: Ask for the voltage rating. Most poly caps will be at least 35 V -- most likely 100V. Anything greater than 25V will be OK.

John

 

Right, sorted (I think )....

So going out shopping for:-

http://www.maplin.co.uk/Module.aspx?ModuleNo=42453
Resistors… as they include 100KΩ & 220KΩ

http://www.maplin.co.uk/module.aspx?moduleno=19079
Diodes…as they have the 1N4002S

[URL="http://[/SIZE"][URL="http://www.maplin.co.uk/module.aspx?moduleno=353"]http://www.maplin.co.uk/module.aspx?moduleno=353
Polyester Layer Capacitors[/URL][/URL]…..Poly Layer 0.1 & Poly Layer 0.01
---do these have a certain polarity or do they just go anyway???---

http://www.maplin.co.uk/module.aspx?moduleno=2704
NE555N Timer

http://www.maplin.co.uk/Module.aspx?ModuleNo=6436
12v Relay - can't seem to find one to go on the PCB so will wire in one of these....

I have found one of these..
http://www.maplin.co.uk/Module.aspx?ModuleNo=2512
12v 12A relay that will go on a PCB, so do you think that will do the trick???


Then hopefully that should stop the brake lights lighting up with 6 volts then, and just come on when they get a full 12 volts......

 

The capacitors should not be polarized and can go in any way. John

 

what do you reckon to this relay...

http://www.maplin.co.uk/Module.aspx?ModuleNo=2512
12v 12A relay

or should I just stick to the ones that I already have??

 

Looks good to me, and is fairly cheap too. I would stick with something that was PCB mounted.

John

 

Cheers for that John,

Will now go out shopping, and hopefully be able to try it out at the weekend, so will let you know how I get on.......

Stu

 

If you have a way to make it on a breadboard first, I might suggest doing that, as there is likely to be some tweaking needed as mentioned earlier for the resistor values or ???.

John

 

well, will hae plenty of resistors to play with the amount that is in the packet I am getting

 

whats the update of this thread been looking for such related topic thanks