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Electronics Plan for huge 7 seg clock from 240V lightbulbs

Discussion in 'Modding' started by bigal, 30 May 2005.

  1. bigal

    bigal Fetch n Execute

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    Ok, this idea started yesterday when i bought a applebox full of 240v 10W bulbs (bayonet fitting):

    [​IMG]

    anyway, i managed (after a lot of sorting out duds from workers from explosive (filimants in 10W's are so fragile they easily cross over and ruduce resistance so much they explode - luckaly all inside the glass but it blew the fuse in the plug of the lamp 3 times) to get 206 good bulbs.

    ANYWAY
    i have decided to make a 6 digit clock, each digit using 18 bulbs for each digit and 16 total in decimal points (4 per point, 2 sets of colons) that is a total of 124 bulbs, plenty spare!

    LAYOUT:

    [​IMG]


    So what i plan to do is drill holes in a piece of thin wood and stuff the bubls through and then just solder directly to the pads on them (this is a eco clock, no bulb holders here!) and make up the segements, so 8 leads per digit, common ground (or anode) and 7 segement wires. that means 28 segements and 1 set of colons to control, mains.

    I need to know if these can be multiplexed and if not is there a circuit available using non multiplexed digits? Or is there other ways of doing this? i thought about relays on the digits but the seconds would be too noisy i guess...

    anyway, any ideas on this.
    basically i am after a non multiplexd clock circuit and advice on switching mains to incandesent bulbs without using relays..

    THANKS
    Alex. :thumb:
     
  2. kbn

    kbn What's a Dremel?

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    SCR's instead of relay?

    Pic to control them - multiplexed, but with flip-flops to non-multiplex them?

    No idea if either of these would be a good idea..
     
  3. Wolfe

    Wolfe What's a Dremel?

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    Use shift registers to controll the digits, though you will need driver transistors.


    That an a microprocessor should do it.

    You can't really multiplex lightbulbs, because they have a long turn-on and off time. (few Milliseconds or more, off the top of my head.)
     
  4. bigal

    bigal Fetch n Execute

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    I assume you mean SSR's (solid state relays) they are too expensive really... if needbe i could just use relays as for obvious reasons (mainly this things going to be about 1KW to run) i am going to have it remote controlled, so you press a button on the remote to switch it on for like 5 seconds, maby also have it come on for 5 secs every hour.

    Been thinking, how about 6 x 7seg - BCD decoders, means only 24 I/O's needed to run it, like a 16f877 ( i have a couple in stock) 32 I/O's total meaning 8 free for buzzers, colon flashing, buttons for time setting, DCF77 etc... :)
     
  5. star882

    star882 What's a Dremel?

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    You can use SCRs to switch the line current if you don't need isolation for the control circuits.
    That will also run the bulbs at half power and increase bulb life as well as save power.
    If you truly want to be advanced, use phase angle control so the bulbs can be faded electronically. You can also use a bridge rectifier (without a capacitor) to allow full brightness.
    Power MOSFETs will also work but then your bulbs will be half on due to the integrated damper diode. Of course, a bridge rectifier or simple diode can fix this.
    Triacs are just about perfect for this application. They're a little harder to drive than SCRs, though.
     
  6. bigal

    bigal Fetch n Execute

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    that isnt a bad idea, only 2 lines per digit too, so 12 data lines... would be hard to code though... you would have to tell it that a 8 = 11111110 (asuming the last shift is not used...)

    would the display flicker during number change during shifting, so relays couldent be used..

    no easy way... :waah:
     
  7. theshadow27

    theshadow27 What's a Dremel?

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    no - shift registers have an OE or output enable line. when this is low, it keeps the current output - on the rising edge it flips to the shifted in signal. that way the bulbs never see the shifting prosses.

    for bulb control, you could use subminatuer reed relays, or TRIACs (the AC version of an SCR) if you wanted to keep it AC... but it will be easier in the end if you use DC. i dont know if this is bad for bulb life though
     
  8. Ghlargh

    Ghlargh What's a Dremel?

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    I remember having a look at a Triac from Onsemi, it has a diagram for running off 5V logic in the datasheet.

    Ofcourse the 5V logic would probably be live, so no touchie, or use optocouplers and a separate isolated 5V, but it would seem like the cheapest way.
    At least it's cheaper than the triac driver opto couplers.

    have a look at the bottom of page 3 of the data sheet for 2N6071:
    http://www.onsemi.com/pub/Collateral/2N6071-D.PDF
     
  9. bigal

    bigal Fetch n Execute

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    hmm. few questions spring to mind:

    Whats a SCR? i thought it was SSR (solid state relay) but obvisally SCR is something else..

    surely reed relays wouldent handle the current?

    like the idea of TRIACS, from my understanding they are like big transistors yeah?

    I may use a standard dimmer switch on the side to vary the common ground of all the bulbs (or maby 3 dimmer switches, one for secs, one for mins and one for hours, as i doubt they handle 1200W!

    liking the idea of shift registers more and more now... so 3 lines per digit, one clocking , one feedign the data and one going high when its finished feeding..
    I guess you could use a common clock..

    Which is easier to code, a clock using 6 BCD - 7 seg decoders or one using 6 shift registers?

    bearing in mind i plan on a PIC 16F877 which has enough pins for 7 seg decoders...


    on a sidenote, i spent a couple of hours reading a tutorial on programming pics (ASM) and my god... :wallbash:
     
  10. SteveyG

    SteveyG Electromodder

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    The output enable simply enables the outputs, it's not controlling latches. So if your outputs are not enabled, there is no output from the shift regs.

    74xx595 has output latches however that would enable the output to be held while you shift your new pattern into the registers.

    Don't forget you can cascade these things. You'd only need 4 (5) lines in total:
    output enable, clock, serial, (reset,) output registers.
     
  11. kbn

    kbn What's a Dremel?

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    I dont really know what they are or how they work but Ill try explaining..

    I think SCR means sillicon controlled rectifier. I understand they are some kind of switch for high power, which people use for railgun/coil gun type projects.

    Triacs are similar and can unevenly alter the frequency in a AC wave but I have no idea how, or how you control them, but they are what is used for mains light dimmers (I think).

    Im not sure if this is relevant, but is there any chips that can be used to convert 1 pin from a PIC, into several outputs. Ive looked at a few logic chip datasheets but most require atleast 3 pins and dont have many outputs...
    Same thing for inputs would also be really usefull.
    The only chips I know of to do this would be a programmed pic :(
     
    Last edited: 30 May 2005
  12. SteveyG

    SteveyG Electromodder

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    An SCR stays turned on while forward biased when a voltage is applied to the gate even when this voltage is removed.

    A TRIAC is essentially two of these connected in inverse parallel, allowing you to get all of your AC waveform through (below and above 0V). So with AC will turn off at the zero crossing point of the waveform (at which point you'd trigger it again for the other half).


    kbn:
    If you could find an asynch/synchronous serial reciever then you could expand your port pins using that. For the synchronous recieved you could either modulate your clock onto the serial, use biphase techniques, or obtain a clock source from elsewhere. Even another uC could be used if you have money to burn.
     
  13. Wolfe

    Wolfe What's a Dremel?

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    You forget that shifting the new pattern into a shift register takes less than a millisecond, so the flicker is not noticeable.

    DON'T Use SCRs. They have a whole host of other issues . Just use transistors. Drive the Bulbs using DC if you have too.

    INcidentally, driving displays with a shift register is easy. Just wire them all the same, and keep track of what means what. It's just cut and paste, as far as coding goes, and you could probably write a subroutine to keep track of them and handle the shift functions.

    Incidentally, you can string a whole host of shift registers together, and drive the whole thing using two data lines. Using lightbulbs, you wouldn't even need to bother with the Enable line. You could just tie it high. With the reaction speed of lightbulbs, you wouldn't even be able to tell when the display shifted.

    Otherwise, the Data and Enable line could be shared, and each register only needs it's own clock line.
     
    Last edited: 31 May 2005
  14. nick01

    nick01 What's a Dremel?

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    It looks to me like the 4 bulbs at the corners require special control because they could be part of either bar. If you are concerned with cost you may want to eliminate them and stick with the standard 7 segment pattern. In your case each segment would have two bulbs and a total of 20W. For that little power there are 6-pin DIP opto-couplers with triac output that you can get under $1, sometimes just $0.20. Look for the MOC30... family like http://www.fairchildsemi.com/ds/MO/MOC3041-M.pdf. Some even come with zero crossing detection, which makes it a little easier for the bulbs (no cold filament at peak voltage) and reduces electrical noise. You may have to split each dot in the colons into two sets of two bulbs to stay within the current limit.

    You mentioned that the bulbs tend to arc when they die. That means they will take any semiconductor driver with them, unless it is one of the expensive SSRs with snubber and all the trimmings. A 270 Ohm/350V-rated series resistor would cut the arc current to a safer level, but it would not cause an excessive voltage drop (10W/240V=42mA, 42mA*270Ohm=11V).

    It will extend the life of the bulbs if you keep them warm while they are "off". A 22kOhm/350V-rated resistor in parallel with the switch (bypassing the switch) should do, but you will have to test that before getting a large number of resistors. Some bulb may already glow vivibly at that current level.

    For control I would follow the microcontroller and shift register idea above. For the registers use 74ACT... or 74AC... family registers, because they drive enough current (24mA) for the LEDs. This one may work and usually is cheap: http://focus.ti.com/lit/ds/schs240a/schs240a.pdf.

    Make sure you sync the controller to the line voltage. For example the shift register could update its outputs only once per line cycle and always on the same direction zero crossing. Otherwise you may get funny beat effects with segments glowing at varying brightness.
     
  15. g0th

    g0th What's a Dremel?

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    Use opto-diac/triac drivers such as MOC3021's to drive triac's such as BT137F's

    [​IMG]

    The current limiting resistor needs an appropriate value of course.
     
    Last edited: 31 May 2005
  16. bigal

    bigal Fetch n Execute

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    good, that helps alot, so i just give a 32bit pattern to the serial line, clocking between each bit.. then throwing OE line high at the end.

    still thinking of the cheapest way of interfacing mains to the logic.. Maby relays are the answer, you get lots on ebay quite cheap... I am wary or running the bulbs on DC due to the dangers involved and rectification. Also relays would reduce risks of damage to the logic on bulb blowouts. I plan to have this setup on a need to know basis, so every hour it come on for like 10 seconds, a keychain remote (about £8 from ebay - 2 chan) could be used to light it on a need to know basis or a simple wire to my desk with a bell type buttton. would make quite a nice noise, i like relay chatter..

    liking shift register alot now.. but as i will be using 16F877's for this which is easier, BCD or SR's ? i would have a hell of a lot of spare I/O's using SR's

    Using relays would require the use of the enable line otherwise it would screw the relays a bit..

    as far as i see it , only 3 lines total as one for data, one for clock and one for OE ? i must be readign wrong, thats insane! why doesnt every clock do that?



    about the bulbs in the corner, EXCELLANT! i had not noticed that, i am glad someone pointed that out, i will have to redesign it like steveys one with no bulbs in the corner... lookout for another MSPAINT design..


    i am sorry, i dont understand what you mean there...?

    i shall think about flow charts etc later, this is a summer holiday project idea so still a month of exams left before construction... :duh:

    think DCF77 though as i think that would be easier than buttons to set, cant imagine this thing scrolling through the time till it is correct... lol... :p


    reguards
    Alex.
     
  17. Ghlargh

    Ghlargh What's a Dremel?

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    (too lazy to quote properly)

    >>Make sure you sync the controller to the line voltage. For example the shift
    >>register could update its outputs only once per line cycle and always on the
    >>same direction zero crossing. Otherwise you may get funny beat effects with
    >>segments glowing at varying brightness.

    >i am sorry, i dont understand what you mean there...?

    I guess he means that if you use a raster to run the lamps instead of giving each segment a separate driver, you should make sure that you allways switch wich raster part is turned on at the same point in the cycle so you don't end up either with different brightness or a scrolling "shadow" over the display.

    this is not an issue if you give each segment it's own individual driver and allways keep the segments lit (the ones that should be lit that is)
     
  18. theshadow27

    theshadow27 What's a Dremel?

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    this only matters if you are using a DC SCR on an AC line. if you use TRIACs, it isnt a problem
    err, sorry i wasnt more specific. you need a serial-in/parallal-out shift register. these will have 8 output pins for the data, clock and OE, but you can stack (i.e. connect all data, clock, and OE lines together for a total of 3 no matter how many you stack) them together for as many outputs as you want... 8 per chip * any number of chips
     
  19. Ghlargh

    Ghlargh What's a Dremel?

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    if you choose to have one driver per segment and a shitload of shift registers, you would only need to update the registers once per second, you would allso get full light on all Lamps as opposed to a raster where you would divide the power by the number of raster segment parts, in this case, probably divided by 3 or 6, depending on if you want to have 14 (6 parts with 8 segments including dividers) or 19 (3 parts with 16 segments) drivers.

    I hope that made sense
     
  20. bigal

    bigal Fetch n Execute

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    side thought:
    I would need 3 separate groups of two shift registers otherwise when the OE line went off and shift loaded and OE high, all the digits would of gone out / dim . relays chatter even if only the two last digits (seconds) needed updating. unless there is a way of shifting new data and only where there is a change does anything change...

    EDIT:

    any ideas on SR's? rapid sell about 10 different ones.. :worried:
     

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