Lite bulb timer project

Discussion in 'The Projects Forum' started by dalewestae, Jan 28, 2013.

  1. dalewestae

    Thread Starter New Member

    Jan 27, 2013
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    Hello friends, I have a project for work and I need some help developing it. I'm sure it is simple for those who know how but I find myself having..... different talents.
    Basically I am looking to take 5 of these- http://littlite.com/products/product/30 that are wired in series. Connect them to a relay that is triggered by a 555 timer will just break the connection with the power supply. The timer will be triggered by a separate device that puts out a 24v dc current.

    If i have confused anyone I'm sorry I will try to reword it.
    I already own two pieces of equipment. The lights, and the device that emits the 24v DC signal when an "attention" button is pressed. I am trying to connect the two with a device that will make the lights flash on and off a (1sec on / 1sec off) for as long as the 24v signal is present.

    I figure if I wire the lights to the relay NC the lights will always be on and when the "Attention" button is hit the timer is engaged and it flashes the lights.

    Thanks
    Dale
     
  2. dalewestae

    Thread Starter New Member

    Jan 27, 2013
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  3. elec_mech

    Senior Member

    Nov 12, 2008
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    Welcome to AAC.

    Let's go through this one step at a time to make sure we understand what you'd like to do.
    1. A 24VDC signal is present when an "attention" button is pressed.
    2. When the 24VDC signal is preset, five bulbs should flash on and off at a frequency of 1 Hz (one second on, one second off).
    3. When the "attention" button is released, the 24VDC signal goes to 0V and the bulbs should turn off.
    Is this correct?

    If yes, you mention connecting these five bulbs in series. The bulbs are rated for 12VDC at 380mA. Placing them in series would require 12 x 5 = 60VDC at 380mA.

    Also note a 555 can accept up to 15VDC safely, 18VDC at its absolute max, so you will need to step down the 24VDC to at least 15VDC to be safe.

    You could use a step-down transformer or step-down voltage regulator to take the 24VDC down to 12VDC. From there, you could use the 555 in astable mode to get close to a 1Hz signal then feed it to either a relay or transistor to power the bulbs. The bulbs could be hooked in parallel requiring 12VDC at 5 x 380mA = 1.9A. As long as your 24VDC signal can safely supply roughly 1.5A or more current, this should work fine. Note (24V x 1.5A)/12V = 3A not counting effiency losses from 24V to 12V conversion, thus the 1.5A requirement.

    The kit you found might work, but note its smallest off time is 2.5s, not 1s. You might be able to switch out one or more of the components to get closer to your 1Hz requirement. You can read more about setting up a 555 in astable mode here.

    Another thought is to use a separate power supply like a wall wart to supply the 12VDC and just use the 24VDC as a signal with no need for any real current. Of course, the 12VDC supply would need to be about 2.5A to be safe or you could replace the bulbs with super-bright LEDs which will require far less current.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,151
    3,058
    Not to be a turd, but that's 0.5Hz, one complete on-off cycle every 2 seconds. ;)
     
  5. elec_mech

    Senior Member

    Nov 12, 2008
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    Doh! :eek: Excellent catch.

    I got mixed up as I've often looked for 1 second clock signals, not on/off combos.

    0.5Hz it is.
     
  6. dalewestae

    Thread Starter New Member

    Jan 27, 2013
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    Thanks so much I do feel like I have a better understanding.
    I love projects like this, and I love that people are willing to share the knowledge to a stranger.

    on to business.
    First I want to clarify on thing...
    Well almost. When the 24VDC is not present the lights are on. When the 24V is present the lights flash. When the button is released 24VDC goes to 0 and the lights go back to steady on.

    There is a wiring diagram on the site that is selling the timer/relay kit.
    http://www.apogeekits.com/images/timer_connection_example.jpg

    Here is my current plant. I will Leave the ground attached to the light from its power supply and reroute the positive wire to the relay. Then wire the lights to the norman closed side of relay. This way the circuit is complete and the lights stay on unless the relay opens.

    We have this 24VDC "attention" signal. If I step down the signal to 12VDC will that trigger the relay to open and close at the determined hz? Thus making the lights turn on and off until the 24VDC goes away.

    Wired something like this...
    http://www.flickr.com/photos/digitaldale/8425121189/in/photostream


    I know I have a problem with the voltage with the lights but step one, I am on the right track
     
  7. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    Okay, to revise:
    1. Lights are constantly lit at all times.
    2. When 24VDC signal is present, lights blink at rate of 0.5Hz (1 sec on, 1 sec off).
    3. When 24VDC signal is removed, lights stay on.
    One note, in your wiring you show the lights connected to N.C. and power connected to N.O. In this way, the light will never get power because the N.O. and N.C. are never connected together. Instead, connect incoming power to COM. Think of relays this way, COM is always connected then you decide if you want whatever is connected to COM to go to N.C. or N.O.

    As long as there is enough current from the 24V-to-12V to power the 555 circuit (< 20mA), yes.

    Still note that the kit you are looking at has a minimum off time of 2.5 seconds. So you could have the lights on for 1 second and off for 2.5 seconds or off and on at 2.5 seconds each.

    If you want to get a 1 second off and on blink rate, someone here may be able to offer a modification you could perform on the circuit. I thought that could be me, but I just looked up the circuit here. I do not follow how this works. They've tied the output to the input and this is simply beyond my current understanding of the 555. If I were doing this, I'd make my own 555 circuit using a generic pre-made PCB following the circuit from here and selecting the right values to get the 1 second timing you're after. This I can help with if you want to make it yourself.
     
  8. dalewestae

    Thread Starter New Member

    Jan 27, 2013
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    Understand the note about the relay.

    The 24VDC signal is 100ma, so I assume it will work. I have read enough to learn that stepping down voltage is not a easy as I thought.

    Finally the off time. Is it not as simple as getting the same potentiometer as the .1 to 1 second? (on time potentiometer)

    Also wanted to say thank for taking the time to help out.
     
  9. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    So long as once you step it down to 12VDC, you get at least 100mA - I just noticed the kit says the input is 12-15VDC at 100mA. Most of that is probably used to energize the relay.

    You could use a 7812 voltage regulator so long as it is able to handle 24VDC. Use with a capacitor on the input and output. One such item: http://www.digikey.com/product-detail/en/KA7812AETU/KA7812AETU-ND/1051269.

    Another thought is to use a 24VDC coil relay to power the circuit with a cheap 12VDC wall wart.

    Not quite. The potentiometers can be adjusted to 0Ω, so making the max resistance lower won't necessarily help. I've studied the circuit and believe I understand it much better now, but the times provided do not match the math I used. It seems the you should be able to set it for 1 second on and off as is, but perhaps I'm using the wrong equations.

    I've started a new thread to help understand how this circuit works as far as timing goes and will report back.
     
  10. dalewestae

    Thread Starter New Member

    Jan 27, 2013
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    You rock my world.
    Thanks so much
     
  11. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    Well, unfortunately no one's responded to my other post on the MK111, so we'll do this old school - I'll build it at home and see what it does. I'll try to do this tonight but can't make any promises. According to my math it should work for your timing requirements but states otherwise. This will be interesting indeed . . .
     
  12. dalewestae

    Thread Starter New Member

    Jan 27, 2013
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    I cant believe that you are taking so much of your own time.
    Thanks so much, I anxiously wait the results...
     
  13. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    Okay, I built it. I didn't have a 47kΩ pot that would fit a breadboard, so I used a 50kΩ instead. Otherwise, all the parts are the same.

    I was able to get roughly one second on, one second off. It worked out to more like 1.15 and 1.45 seconds, but that is due to the pots. Single-turn potentiometers are difficult to set at a precise value.

    Here is a quick and grainy video I took with my cell that shows two LEDs, one to show on time, the other off time: http://youtu.be/TsVJSoXgBxA.

    Here is another video showing only one LED to give you a better feel for how your lights would look: http://youtu.be/8ripy_QC37o.

    I'd suggest replacing the pots included with the kit with multi-turn pots at a lower resistance. When I measured the resistance of the pots at the rough one-second timing, RV2 was at ~2.7kΩ and RV1 was ~15kΩ. Mathwise, 15kΩ is ideal, not sure why the 2.7kΩ is what it is - perhaps I measured it wrong. I think if you went with something like 10-, 15-, or 20-turn 20kΩ pots, you'd be set and could get it really fine-tuned.

    The only difficulty is a multi-turn pot will have three pins in a row whereas the included single-turn pot pins form a triangle. You could bend the middle lead of the multi-turn pot and may need to solder a longer lead to reach the middle hole on the PCB, but that's not too hard.

    If you have a separate 12V supply for the lights, you could connect the positive lead in series with a 24V coil rated relay (COM and N.O.). Then connect your 24VDC signal to the relay's coil. In this way the lights and circuit are powered by the 12V source and the timing circuit is controlled by the 24VDC without worry about pulling too much current - so long as the 24V relay coil does not require more than 100mA. If you do this, be sure to put in a relay across the coils like D1 is used in the circuit.

    The kit you originally posted is an assembled kit. If you're okay with getting close to one second on and off, then this is fine. If you want to change out the pots, I suggest buying the part form of the kit which requires you to solder the parts on. This allows to use a different pot - much easier to solder on a new pot than desolder one from a completed board. If you can solder and want to change the pots, I suggest this:
    http://www.mcmelectronics.com/product/28-12868 (unassembled kit on sale for under $4)
    http://www.mcmelectronics.com/product/500-0202 (25-turn pot - you'll need two)
    http://www.mcmelectronics.com/product/R24-5D10-24V (not cheap, but this relay would allow you to use the 24VDC to turn on the timing kit if you opt to power the kit with the 12V for the lights; you will have to solder the wires though).
    http://www.mcmelectronics.com/product/118-1N4148 (diode to protect relay's coil)

    Let me know if you need a diagram showing how to connect the separate 24V relay to the timing circuit.

    Hope this helps.
     
  14. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
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