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Please help me with a project!

Discussion in 'General Electronics Discussion' started by furbious, Sep 28, 2012.

  1. furbious

    furbious

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    Sep 28, 2012
    :confused: Hi there,

    I am a complete newbie when it comes to electronics. But, I am a craftyish person have a project that won't stop bugging me until I've made it.

    My boyfriend loves Portal, insanely so. I want to make him a companion cube storage box with glowing hearts for our anniversary. (Please look up companion cubes if you're unfamiliar with them!) What I want to do is have a smallish storage box covered with fabric/vinyl, and have the hearts with a clear or red transparent cover over a cluster of LEDs that glow/throb. I'd like all six sides to throb in unison, and to all run from one battery/power pack that's hidden in the bottom of the box. I'd also like it to be able to be turned on and off with a switch or button or something. The approx size I'm looking at is a box 6" cubed, so the furthest cluster would be around 15-18" away from the circuit.

    I've looked up some websites and tutorials etc and you guys lost me somewhere between breadboards and 555 somethings. I think I understand how to get one LED to throb, but it's attached to the circuit/breadboard and I don't understand how to get six strings of LEDs to run from one circuit. Is that even possible?

    tl;dr I would like to know how to have six clusters of 3 LEDs to throb in unison and run off one power supply, ie a battery pack, and have the clusters able to be at some length away from the circuit.

    If anyone has some information, or if you've got a tutorial that I haven't managed to find, I would greatly appreciate it!

    Thanks,

    Furbious
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Why should we have to hunt them down? Post a link.

    Chris
     
  3. wingnut

    wingnut

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    Aug 9, 2012
    Suppose you can get 1 led to flash, as you said.
    Take the lead to a ULN2003 chip and split this input into 6 inputs going into the left pins of the ULN.

    From the output (right) side of the chip, take 6 strings of 3 LED's each string with a 33 ohm resistor. The ULN is a cheap and easy chip to understand and work with. I am assuming a 6V power supply.



    This web site has a nice wizard to help you design arrays of LED's
    http://led.linear1.org/led.wiz
     

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  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Heartbeat throb on LEDs

    This may not be useful to the OP but I liked the idea of making LEDs "throb" like a heartbeat, so I designed this circuit. It's not suitable for a beginner but might be useful to others in future, so I'm posting it here.

    [​IMG]

    Here's the design along with a simulation showing the current in the LED chain.

    U1 operates as an astable with a duty cycle of around 4:1 and a period of about 1.15 seconds (corresponding to about 52 beats per minute). Both rising and falling edges of its output are used to forward-bias Q1, to generate the two beats in each heartbeat cycle.

    When U1 output goes high, a broad positive pulse is created by C2 and R3, and coupled through D1 and R4 into Q1, causing a long burst of conduction in Q1, which charges C3 (through R6) to about 80% of the supply voltage. When U1 output goes low, the top end of R3 briefly goes negative; this is coupled through D2 to the emitter of Q1. The base of Q1 is pulled to 0V by R4 and D3, so this negative pulse on the emitter causes a short burst of conduction in Q1, which charges C3 to about half the supply voltage.

    C3 is discharged by R7. Q2 buffers this voltage, and D4, D5, R9 and R10 divide the waveform down to about 1V peak to peak, with compensation for the base-emitter voltage drop in the variable current source transistors.

    Each string of three LEDs is driven by a variable current source consisting of a Darlington transistor with 33 ohm emitter resistor. The LED current waveform is shown. LEDs generally don't have a linear relationship between forward current and brightness, so the subtleties in the current waveform may not be very visible, unfortunately.

    In a practical implementation, the two transistors connected as a Darlington would be replaced by an actual Darlington transistor such as an MPSA64. (LTSpice doesn't seem to have any Darlington transistors!) Also, the part values I've used in the simulation for the red LEDs are probably wrong; I just chose something at random from the limited options provided with LTSpice.

    Multiple LED chains can be driven using multiple variable current sources - i.e., duplicate the Darlington transistor and emitter resistor for each LED string.

    The circuit is shown with a 12V power supply, and this is needed with the LED types I've used, which seem to have a forward voltage around 3V. Typical red LEDs have a forward voltage closer to 2V so the circuit might work from 9V with these. If in doubt I would stick with 12V.

    Each chain's peak current is about 21 mA so with six chains, peak current drain is around 130 mA. A PP3-type 9V battery is probably not suitable; I would use a battery of eight AA or AAA cells in a holder.

    To the OP. This circuit is probably way more than you want. I posted it here because it uses a couple of ideas that other forum members might find interesting. In answer to your questions, LEDs are normally connected in "strings" (as in my design) with either some circuitry or just a series resistor to limit the current. See Steve's excellent article https://www.electronicspoint.com/got-question-driving-leds-another-work-progress-t228474.html. You can connect them in strings of three by just soldering their leads together (make sure to observe polarity), with a current limiting resistor in each string, and drive all the strings in parallel from a common signal using two wires that you run around the inside of the box. Also, red LEDs are very RED so you might want to use a pink-coloured plastic heart lens to improve the colour. You can get larger LEDs - 10 mm diameter, and 20 mm diameter dome-shaped things, which may suit your purposes better. Check out alibaba.com, they have various heart-shaped LED products, but beware of the minimum order quantities!

    In practice, this whole circuit would be easily and cheaply replaced by a very small microcontroller using an internal clock, a waveform table, and pulse width modulation to control the LEDs, providing a smaller, simpler, cheaper and better solution.
     

    Attached Files:

    Last edited: Sep 28, 2012
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Nominated The Most Clever Circuit Award

    There's no doubt about that but a uC can't come close to the charm of your circuit. Did you pull the Q1 & Q2 design from something else you designed previously? I ask because the OP posted this only yesterday!!

    If we had a 'Most Clever Circuit Award' I think you'd rein King of the hill for quite some time. ;)

    Since I crippled my sciatic nerve, a week ago, I've been in excruciating pain. I was beginning to think that I'd never smile again.

    Thank you for the smile! :)

    Chris
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    No, but I may have previously used the trick of coupling positive and negative pulses onto the base and emitter of one transistor to combine them together.
    Thanks Chris :)
    Oh dear, that sounds serious...
    Thank you for the kind words :)
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Now we do! :) here
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Steve, thanks for doing that but it needs it's own title. You did provide a direct link to Kris's post but how else are we to add to the nominations if doesn't have its own thread?

    Chris
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Thanks guys :)
     
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Just don't let that head get too big. You may want to take precautions. If you can't find a belt that size.. duct tape is OK in a pinch. :p

    Congrats!

    Chris
     
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Don't worry, I've got that sorted!

    [​IMG][​IMG]

    It's been working so far :)
     

    Attached Files:

    Last edited: Sep 29, 2012
  12. wingnut

    wingnut

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    KrisBlueNZ - my LTspice has darlingtons. I joined their user group and downloaded a later version with much more.
     
  13. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    wingnut, is that the TIP121, 122 and 127 set from the library?
    I joined the yahoo group too, and downloaded the 2012-08 library, but those are the only Darlingtons I can find in it.
    Re your version of LTSpice with "much more", was this a single installation that contained a lot more library files? If so, do you know the URL you downloaded it from? It sounds like a better installation than the one I got from LTC...
     
  14. wingnut

    wingnut

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    Aug 9, 2012
    It was LTSpiceIV_Plus_12_2009 and has at least 10 Darlingtons.

    It was a one-off download that had far more than the first version I downloaded.

    Sorry, I dont have the URL but it is somewhere on that usergroup.

    If you cant find it, I see the option of compressing it as a rar file and emailing it to you.
     
    Last edited: Sep 29, 2012
  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    wingnut, I've found the thread on the LTSpice yahoo group. It seems that that distribution is a mixture of files from various sources. Helmut, the moderator, doesn't recommend it. See http://tech.groups.yahoo.com/group/LTspice/message/33517

    In any case it's no longer available from 4shared.com.

    As often happens with freeware, you're a bit on your own with LTSpice. There's no point asking Linear Technology to add Darlingtons to their distribution - they don't make Darlingtons, and their attitude would probably be "just be grateful for what you get". It's lucky there are those yahoo groups, and Helmut has collected lots of stuff into a library, but it's not documented. Par for the course. Thanks for your help.
     
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