DIY Sequential Taillights for approx $20

[brettsimons]

Well I think I jinxed it... haha after I posted my last update with the load resistors, I got two more error messages. Granted it is a lot better than yesterday where the BCM almost everytime I drove my car, I don't understand why it isn't fixed 100%. Normally I could troubleshoot myself but it seemed to be completely random... no pattern or similarities between the three situations! :( The first two were starting up from a light roughly around 6:50 AM and 5:15 PM and the third one was slowing down when I was getting off of the interstate at around 7:10 PM...

[brettsimons]

Nevermind I just ran the calculations again and realized that at my 6.9 ohms if my voltage drops to 12 volts, then I'm .3 amps less than what the BCM is expecting of 2 amps which might be enough to set it off?

[Highlifeman]

You had the brakes or blinkers on in all the situations though, right?

It could be that your load resistors combined with the light bulbs are drawing too much current and causing the errors. Try out the circuit I posted using two MOSFETs and use the idea I had to include the 6 ohm resistor in place of the 1000 Ohm resistor. See posts 174 and 176.

[sjmautoprod]

Originally Posted by brettsimons

Nevermind I just ran the calculations again and realized that at my 6.9 ohms if my voltage drops to 12 volts, then I'm .3 amps less than what the BCM is expecting of 2 amps which might be enough to set it off?

Sounds right.

[pkauf]

Originally Posted by Highlifeman

Well, I didn't realize the 555 timer in the original schematic was sinking the relay, so it was actually correct that an P-type or PNP transistor would be needed if you wanted to do it with only one transistor.

Anyway, here is a couple of schematics showing how to do it with two MOSFETs or a MOSFET and an NPN transistor. All the components on the left side are the same as the original schematic in the thread. All of these components should be available locally at any Radio Shack.

I can't guarantee that the bottom one will work with those resistor values, but it should. If it doesn't work, going to a smaller resistor for the 91K should make it work. I did one with the NPN because it should be cheaper and smaller, but both may be negligible. However, I can all but guarantee the top one will work, so that may be the better choice.

Edit: Replace the 1K resistor with a 6 Ohm, >35W resistor to get a constant current draw from the lights. It would serve the function of the "load resistor" previously mentioned.

Would it be possible for you to post a recommended list of Digikey part numbers for this approach?

Thanks

Paul

[Highlifeman]

Originally Posted by pkauf

Would it be possible for you to post a recommended list of Digikey part numbers for this approach?

Thanks

Paul

Sure, that is much easier than being limited to Radio Shack's crappy selection. This is for the top circuit in my drawing with two MOSFETs and replacing the 1K resistor with a 5.6 ohm.

MOSFETs x2: 2SK4017Q-ND
555 Timer: 296-21753-5-ND
Diode: 1N4001-E3/54GITR-ND
Capacitor: 445-8552-ND or P5148-ND
Potentiometer: DJA15TB-ND
Resistor: TCH35P5R60JE-ND (You could also use the big power resistor shown earlier in the thread, but I couldn't find it on Digikey.)

You will also obviously need a board to mount the stuff on and wire to connect it.

[pkauf]

Originally Posted by Highlifeman

Sure, that is much easier than being limited to Radio Shack's crappy selection. This is for the top circuit in my drawing with two MOSFETs and replacing the 1K resistor with a 5.6 ohm.

MOSFETs x2: 2SK4017Q-ND
555 Timer: 296-21753-5-ND
Diode: 1N4001-E3/54GITR-ND
Capacitor: 445-8552-ND or P5148-ND
Potentiometer: DJA15TB-ND
Resistor: TCH35P5R60JE-ND (You could also use the big power resistor shown earlier in the thread, but I couldn't find it on Digikey.)

You will also obviously need a board to mount the stuff on and wire to connect it.

Thank you so much!!!

[dragom]

ok what is the verdict on using the 2 MOSFETs does the error message from the BCM go away has anyone tested this yet??

[hapisok]

i worked the double mosfet on my bread board and had no luck. changed out resistor values and still nothing. gonna keep working at it.

got the P-type to work...kinda. need to figure out the resistor value to go inline from pin 3 to the gate as it lights up (dim) as soon as power is applied and goes full on once the timer counts down. need to limit the voltage going to the gate of the P type until "time on".

[Highlifeman]

That's strange. Can you elaborate on what happened with two MOSFETs, or did it just not light up at all?

Putting a resistor in between the timer and the gate of the transistor won't do anything. Current into the gate is zero, so there will be no voltage drop across the resistor.

[dragom]

I got most of the parts to do either way but will wait and see which one works best before I order anymore parts. The price for everything has slowly gone past the 20 dollar mark.

[hapisok]

Originally Posted by Highlifeman

That's strange. Can you elaborate on what happened with two MOSFETs, or did it just not light up at all?

Putting a resistor in between the timer and the gate of the transistor won't do anything. Current into the gate is zero, so there will be no voltage drop across the resistor.

With the 2 mosfets, nothing happened, no lights. Used a variable 1k resistor and swapped it out with various resistors at lower ratings to include 5ohms.

For the P type mosfet, does it need a pull down or pull up resistor between the gate and Vcc?

[Highlifeman]

Originally Posted by hapisok

With the 2 mosfets, nothing happened, no lights. Used a variable 1k resistor and swapped it out with various resistors at lower ratings to include 5ohms.

For the P type mosfet, does it need a pull down or pull up resistor between the gate and Vcc?

That resistor value doesn't matter much, it's just to limit the current going through the MOSFET. It sounds like it may be hooked up to the wrong wires, or hooked up backwards. If it's on the wrong wire going to the bulb then switching the wires going to the "input" and "to light" terminals should make it work.

If anyone has a wiring diagram of the tail lights, it would help me out a ton and I could say which color wires to hook it to. Or I guess I could get out the multimeter tonight and figure it out.

For a P-type, it shouldnt need a resistor between the gate and Vcc. Current cant go into or out of the gate, so a resistor before it doesn't do anything. To use a P-type, just connect the gate to pin 3 on the timer and think of the drain and source as the contacts on a relay, except polarity matters.

[Highlifeman]

Originally Posted by hapisok

i worked the double mosfet on my bread board and had no luck. changed out resistor values and still nothing. gonna keep working at it.

got the P-type to work...kinda. need to figure out the resistor value to go inline from pin 3 to the gate as it lights up (dim) as soon as power is applied and goes full on once the timer counts down. need to limit the voltage going to the gate of the P type until "time on".

After thinking about it some more, it sounds like you cut the negative wire from the light bulb. Try hooking it up to the other wire going to the bulb instead.