Circuit that will delay the turning on of a light

[Shadow787470]

Im trying to design a circuit that will delay the turning on of a light.
I have three bulbs, one should turn on as soon as power is applied, the next should turn on in X amount of time after the first, and the final light should turn on in X amount of time after the second.
Basically like this
[on][off][off]
[on][on][off]
[on][on][on]

I believe ther center circuit in the picture I am attaching is what i need to use and i picked one up from radio shack but i don't have some of the other parts i would need (all i have are some various resistors and capacitors and other odds and ends from my circuits class)

So what would you guys reommend doing? I can't seem to find a formula to calculate the proper values of the resistors and capacitors so that the time X will be the value i need it to be.

Here is what I am trying to accomplish

 

[Shadow787470]

50 view and no one has any input or guidance? I've googled 555 circuits and tried to find more info but apparently there is a LOT of things you can do with these

 

[Fish4Fun]

Shadow,

Welcome to PF!

I would suggest you use a micro-controller, though you could certainly use discrete logic or a PAL with a clock source. 555's are great for some things, but not really well suited for what you are attempting to do.

I would assume you are attempting to do a "Red, Yellow, Green" starting light? The timing of this type of circuit is usually fairly important, and I would never trust a 555 (much less three of them) to a timing sensitive project.

A $3 micro-controller, 50 lines of assembly code and a 5V wall-wart and you can drive 3 LEDs or logic level mosfets with extreme accuracy. If you want to use 120Vac light bulbs, you would simply replace the LEDs with opto-Triacs and add three suitable power triacs.

Fish

 

[Fish4Fun]

Ooops, I missed the picture of your tail-lights. Definitely use a micro-controller. You will need a voltage regulator to bring your 12V to 5V (If you are planning on using one device for each tail-light, and powering it only when the tail light is "on", you could get by with a zener, a resistor and a capacitor). A simple uController with internal clock. Three logic level mosfets. Very simple design, very simple firmware.

Fish

 

[Shadow787470]

Ooops, I missed the picture of your tail-lights. Definitely use a micro-controller. You will need a voltage regulator to bring your 12V to 5V (If you are planning on using one device for each tail-light, and powering it only when the tail light is "on", you could get by with a zener, a resistor and a capacitor). A simple uController with internal clock. Three logic level mosfets. Very simple design, very simple firmware.

Fish

Thanks, i have no idea what half of the stuff you mentioned means but ill start looking into it.
Also with the controller you can set it up so that once the light it turned on it won't turn back off until power is remover correct? These need to function when brakes are applied as well as turn signals. When the brake is applied they should go through the normal delay function then remain light until power is removed.

For the voltage regulator could i use this?
http://www.radioshack.com/product/index.jsp?productId=2062599
And would i need a heatsink? it says some applications may require one.
Also would it be hard to design this using LEDs at first to get it working correctly then just swap it into the tail lights?

 

[davenn]

if the current drawn is 1 amp or less, then yes that regulator would be ok :)
and for anything over 0.5A it would definitely need to be heatsunk. It WILL get hot

I can't help with the micro controller... not my field sorry

Dave

 

[dlgoff]

I did a little googling and came up with this site: http://home.cogeco.ca/~rpaisley4/LM555.html#24"

You may have to adjust some of the component values but this one may be of interest:

 

[davenn]

ahhh interesting... from the same site as the OP's ccts :)

just looking at the timing tho... if I read it correct... it doesn't match what Shadow is trying to achieve... see the taillight animated gif in his first post.
the timing shown shows that the following timer doesn't trigger till the previous one switches off.
Rather what is needed is just 3 independant timers starting with the same trigger ...
1st timer triggering immediately but not switching off till end of full cycle
2nd timer triggering after a delay but not switching off till end of full cycle
3rd timer triggering after a longer delay but not switching off till end of full cycle

at end of full cycle all 3 switch off and start sequence over again

Dave

considering that the start pulse is supplied by activating the turn signal level...
1) can the three pin 2 trigger inputs be tied together and just use the single .01 and 100k as shown above the "start" switch or does there need to be some isolation ?
2) would/could you need/use a 4th timer to trigger the reset automatically, till the turn lever resets to centre position after completion of the turn ?

 

[Shadow787470]

as far as i know when the turn signal is applied the tail lights receive a pulse of power, where are the brake sends a constant power supply. If that is correct then i only need to set it up so that the time it takes for all three lights to turn on is <= the turn signal pulse so that it will sequence each time it is powered but will remain on after 1 sequence when the brake is applied.

here is a video on youtube of how they should work. I am trying to recreate this exactly

 

[dlgoff]

Lights in autos has changed a lot over the years, but usually, tail light bulbs have two sets of filaments. One for the turn signal and one for the break.

 

[Shadow787470]

Lights in autos has changed a lot over the years, but usually, tail light bulbs have two sets of filaments. One for the turn signal and one for the break.

Hmm, ill have to look into that as far as my car goes (07 mustang)
Some more googling revealed this diagram.

perhaps this would be better for my application? I am trying to keep it as cost effective as possible and i don't have much knowledge in electrical engineering (im mechanical)
also with the diagram i just posted is that something i could build on a breadboard with 3 leds to test it out? The circuit looks fairly simple compared to some I've put together but i have no knowledge of what kind of currents and voltages i could use to test this on leds and then use on tail lights aswell

 

[FulForceOfChi]

I don't know much about Micro Controllers but maybe that is the thing you need to look into, you can set basic timer systems with delays into any circuit. You will need a regulator but the previous posters pretty much gave you a sound circuit so take the fore-mentioned advice. ^^

Watch out for over-heating

 

[Bob S]

This site

http://www.gofastforless.com/electrical/lights.htm

recommends this circuit

http://www.gofastforless.com/electrical/sequence-control.jpg

and

http://www.gofastforless.com/electrical/sequence_control.gif

where the NE556 is just a dual NE555. The two relays can be replaced by two TIP42G PNP transistors, available at Radioshack:

http://www.radioshack.com/product/index.jsp?productId=2062613

Use 220-ohm 1 or 2 watt pulldown resistors to limit the base current to about 50 mA.

Bob S

 

[Shadow787470]

This site

http://www.gofastforless.com/electrical/lights.htm

recommends this circuit

http://www.gofastforless.com/electrical/sequence-control.jpg

and

http://www.gofastforless.com/electrical/sequence_control.gif

where the NE556 is just a dual NE555. The two relays can be replaced by two TIP42G PNP transistors, available at Radioshack:

http://www.radioshack.com/product/index.jsp?productId=2062613

Use 220-ohm 1 or 2 watt pulldown resistors to limit the base current to about 50 mA.

Bob S

That looks like what i need. With the pots i can just replace them with resistors once i get the timing down correct? And to change the timing i just change the resistance? Will one of the pots need to be twice the value of the other to get the timing correct or will they remain equal?

Also I've never wired a relay before so i don't fully understand the diagram where it comes into play. I see there are are 3 nodes involved one if which is part of the switch. Which node corresponds to which wire on the relay? After a little bit of searching I've found that there is a NC NO and COM and I am thinking the NO is the one that's connected to the switch. COM is the first one coming out of 9 and NC is the one after the COM?

Also i really appreciate all you guys helping me out. I've really wanted sequentials for my car for quite some time but they run at least $100 and seeing as I am in school for engineering it seemed like a good idea to try and make my own

and can i use LEDs in place of the relays just to get it dialed in? i have access to plenty of resistors and capacitors and it would be a LOT easier to do this small scale first before tearing into my car

 

[Bob S]

As a first attempt, I would try ≈10k and ≈20k resistors in place of the two pots. The larger the resistor, the longer the delay. They could end up being as much as 25k and 50k, depending on your needs, flasher switch, etc..

If you decide to use relays, NO, NC and COM stand for normally open (only when power is off), normally closed (only when power is off), and common. I would be a little concerned about the inductive voltage spike across the coil when the relay opens. A reverse diode across the coil (1N4001,4002,4003) might be a good idea.

If you start out by using LEDs instead of relays, put a ≈500 ohm resistor in series to limit current.

Bob S

 

[Shadow787470]

As a first attempt, I would try ≈10k and ≈20k resistors in place of the two pots. The larger the resistor, the longer the delay. They could end up being as much as 25k and 50k, depending on your needs, flasher switch, etc..

If you decide to use relays, NO, NC and COM stand for normally open (only when power is off), normally closed (only when power is off), and common. I would be a little concerned about the inductive voltage spike across the coil when the relay opens. A reverse diode across the coil (1N4001,4002,4003) might be a good idea.

If you start out by using LEDs instead of relays, put a ≈500 ohm resistor in series to limit current.

Bob S

Would i only need the 500 ohm resistor if i were testing with a car battery? Id like to get it set up with a few AA batteries (i suppose i would need a 12v source so the timing would match that of the car?) running correctly before trying to integrate it into the actual tail lights.

Here is what i was thinking i could do as a trail but I am not sure if i have it right (also i think i have the two leds on the right side backwards)
[PLAIN]http://img594.imageshack.us/img594/9335/modifiedsequence.jpg

 

[Bob S]

The polarity of the two LEDs on the right side should be reversed, so the LEDs are forward biased when the NE556 outputs 5 or 9 are low.
Also, an approximately 500 ohm resistor should be in series with all LEDs to limit the ON current. This resistor is required any time the
input voltage is 12 volts, either a car battery or 8 AA batteries. (The two output LEDs may glow faintly when the outputs 5 or 9 are high.
This is not a problem, but due only to the totem pole outputs never reaching a full 12 volts).

Bob S

 

[Shadow787470]

The polarity of the two LEDs on the right side should be reversed, so the LEDs are forward biased when the NE556 outputs 5 or 9 are low.
Also, an approximately 500 ohm resistor should be in series with all LEDs to limit the ON current. This resistor is required any time the
input voltage is 12 volts, either a car battery or 8 AA batteries. (The two output LEDs may glow faintly when the outputs 5 or 9 are high.
This is not a problem, but due only to the totem pole outputs never reaching a full 12 volts).

Bob S

I realized the leds were reversed right after i uploaded the image. Aside from adding the resistors before the leds does everything else seem good? Also does the timing depend on the voltage supplied? Id hate to set it up on a 9v battery and then the timing be off when on the cars battery.

Once i get it working all i have to do is replace the 3 leds with relays right? (or the 2 that are delayed atleast, the other can be hooked up like normal)

 

[Bob S]

I realized the leds were reversed right after i uploaded the image. Aside from adding the resistors before the leds does everything else seem good? Also does the timing depend on the voltage supplied? Id hate to set it up on a 9v battery and then the timing be off when on the cars battery.

Everything looks good. According to the NE555 (and 556) datasheet, the delay time is about 1.1·R·C, where R and C are the circuit component values. Thus the delay times should be independent of input voltage. The LED brightness will depend on the input voltage, however.

Once i get it working all i have to do is replace the 3 leds with relays right? (or the 2 that are delayed atleast, the other can be hooked up like normal)

. Remove the LEDs and series resistor, and replace with 12-volt relays. You might consider using a reversed diode (1N4001, 4002, 4003) directly across the relay to prevent inductive voltage spikes from getting back into the IC. Sometimes, people put a forward biased diode in series with the relay instead. Have some spare NE555's or 556's just in case.

Bob S

 

[Shadow787470]

One last question. I am assuming the power wire for the tail lights has quite a bit more current then the IC can handle. How do i step this down so i can power my circuit? I would like to have the power wire that goes to the lights both power my circuit and connect to the relay that powers the lights. Are there any potential problems with that?
Ive spent the past few days playing around with leds and looking up PCB prototyping and need to get back on track as to how it will work in the car.
I still need to dial the timing in but currently i don't know the timing cycle of the turn signal.

Is the formula
Delay time =1.1 R C
correct? And how accurate is this formula? I am not sure how precise i can measure the light cycle but I am guessing its small