Back to the 555 - What next?

Discussion in 'General Electronics Chat' started by CoachKalk, Sep 29, 2011.

  1. CoachKalk

    Thread Starter Member

    Sep 20, 2011
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    I have been working my way through the basics for a few projects. I had some luck with the 555 and then moved on to a few other components that I was struggling with a bit.

    I have attached a circuit that I made (free software, and my first time so please overlook the mistakes).

    I think I included most of the relavant info. Please let me know if I missed something. It may be blind luck, but the circuits works like I wanted it to. I really tried to follow some circuits I found and tried to build/modify it with what I had. Laser hits the LDR and the green LED comes/stays on. No laser, buzzer starts buzzing.

    I know the circuit shows 18V and the MAX for the 555 is 18V, but the measured Vcc was actually less (2 9V's, 1 used some). I wasn't sure what the correct method of labeling would be.

    Unless you guys tell me I need to fix major items, my next steps and therefore questions to you guys are:
    1. I have used batteries so far, but I would like to use a power supply for these circuits. I would like to use some large, push buttons I have found to "Start" the sensor circuits (plan on 3 separate ones). Desc: Momentary-action, S.P.D.T lighted pushbutton switch for displays and games. Rated 5 Amps @ 125/250 Vac. The assembly is lighted with a replaceable 12 Volt, 3 Watt, #161 wedge-base lamp. I have not even started looking into power supplies. Based on the level of difficulty, would it be better for a newbie to purchase something?
    2. I plan to have Flashing lights start if/when the light is broken. I am looking at: Protected against polarity reversal. Fully Sealed and waterproof. Power output: 1W. Power supply: 12 Vdc I know the buzzer I have used for the proto is 12V, but I have also found some flashers with sirens. I was not sure about how/what my options were coming out of the circuit so I stayed in the smaller range. If I go with the flasher listed above, can I just use the current setup?
    3. And finally, to hyjack my own thread. I have been looking into 2 other projects - Game Show Type Set-Up and Finding a Set-Up to Measure Speed of Some of my wrestlers doing certain moves. Can I use a similar circuit in these 2 projects? I know the light/dark would have to be tweeked because we do not do a lot of wrestler practices in the dark. Maybe some sort of motion indicator? Could I dial in the sensitivity with the pot. to still use the laser/LDR set-up? I was strugging with a circuit I found to trigger a stopwatch on and off, but I was thinking I could use this if the sensitivty was there.

    Sorry about the novel. It is very late and I was rambling a bit there. I will say this site has been an incredible resource. Not only the forum, but the info listed as well.

    THANK YOU!
    Steve
    [​IMG]
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    A standard 555 max voltage is rated at 15VDC. Why not use a single 9V battery instead?

    I suspect you have been reading my articles (thank you!), especially judging the schematic you have drawn. You can use the templates I've made up for M/S Paint (which is what I draw in) on my blog.

    Bill's Index

    Introduction and PaintCAD

    I would be more help if I could, but I just got home from work, and I am both tired and sleepy.
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    While your circuit may work I would have tackled it differently. I would separate the laser sensor section from the buzzer section. The 555 timer's main function is to generate an oscillating voltage to make an LED flash or make a buzzer sound.

    The function of the laser detect circuit is to detect when the laser beam is interrupted. You can do this with an opamp, a comparator, or even a single transistor. The output of this will be used to trigger your light and sound. For a buzzer that requires higher voltage or current, I would consider using a mechanical relay to turn on the buzzer.

    You may determine that the LED or buzzer should come on for a certain length of time. For this you can use a monostable multivibrator. There is a 555 configuration to do this. (If the requirements get more complex than this, a small microcontroller is always an attractive solution.)

    I would agree with Bill Marsden and go with a single 9V battery.
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    There's nothing wrong with re-purposing a 555 to do things besides timing. There was just a huge interweb contest for the most creative re-purposing of the 555.

    Using pins 6&2 like this you bring out the comparators that set the output flip flop so you get a very good voltage detector with a large dead band in the middle (and that's a good thing). You also get the hefty output drive of a 555 to run the light and buzzer.

    (V is a better choice for power in. The 12V buzzer may well make lots of noise at 9V and that's simple enough to check, right? I can't see the resistor for the LED but may be OK too.

    I recently posted an Ikea night light that uses this same configuration. It's a solid circuit, really.
     
  5. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Using two 9V batteries may or may not be necessary for the buzzer - test a single 9V battery. If two are necessary, the using a 12V or 15V Zener to clamp the voltage below 18V. Two new 9V batteries may produce 19V - 20V for a short time and shorten the life of the 555.
     
  6. CoachKalk

    Thread Starter Member

    Sep 20, 2011
    139
    2
    Thanks for the input everyone. I am new to this arena so I am still learning what components best perform which function. To be honest, the 555 tutorial/experiments were so well done, I just decided to try to use the 555 when/if ever possible. It may very well be like driving a Porsche to go get groceries, but at least I have a relatively good understanding of the pin functions. (5 and 7 still kind of confuse me some - I need to find some circuits that show these in use just to get myself more familiar).

    I may have made an incorrect assumption about the V needed for the buzzer. I couldn't locate the original part number/bag and the only info provided on the buzzer itself is 12VDC. When listed like that, is that simply a MAX V that the buzzer will handle? The purpose of 2 9V's was to get my Pin 3 output above the 12V and then back it down with a resistor. That thinking may be whacked as well - surprising what you can convince yourself of working into the wee hours all alone.

    As far as powering these circuits. I have an old computer power supply that looks to like a tank 110VAC in, 12V 18A MAX, 5V 40A MAX Max Output Power is 425W. I am assuming this is overkill city, but it is sitting collecting dust. Is it worth trying to take it apart to figure out the tangle of wires with motherboard adapators or just go to radio shack and get a plain Jane converter? I am looking at large game style push buttons to turn the sensor circuits on/off. Another stupid question here - the rating listed 5A @ 125VAC is MAX correct? I can just as well use this for the DC line after the converter? Just a mechanical style switch right?

    The output options based on my limited understanding: (Assuming staying with the 555) Pin 3 output Voltage will be V(source) - 1.7V. So,
    1. Directly feed a circuit/"stuff" that is happy with the Pin 3 output. Like the circuit I have drawn up.
    2. Feed a relay (as mentioned above) that will complete an entirely different circuit/power supply.
    3. Modify/increase the Pin 3 output voltage then "keep truckin'" (without relay, just directly into next circuit).

    If I end up going with a siren/flasher that is 110 AC, option 2 is the only option right? Just use the output to get a relay coil to activate and be done with it?

    Thanks,
    Steve
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Pin 5 is the CTRL input, and normally sits at 2/3 of Vcc. If you decrease the voltage on pin 5 when the timer is in an astable configuration, it will speed up, and it will spend less of its' time with the output high.

    Pin 7 is an open-collector switch. A classic use for pin 7 is shown as an astable configuration; R1 goes from pin 7 to Vcc, and R2 goes from pin 7 to pins 2 & 6 - then timing cap C1 goes from pins 2 & 6 to ground. When the cap is charging (pin 3 is high, pin 7 is off) the current charging C1 flows through both R1 and R2. When the threshold level is reached, pin 3 goes low, and pin 7 is shorted to ground internally. You have to watch out for this 2nd part; if you have too low of a resistance value for R1, you can burn up the timer IC. I suggest no less than 100 Ohms per volt of Vcc.

    As far as the buzzer voltage - if it was originally labeled as being for 12v, then you shouldn't exceed that.

    9v pp3 "transistor" batteries have very little power, and are expensive.

    As far as the computer supply, if it's an ATX or ATXplus12 form factor supply, you can google "ATX bench supply" for lots of ideas about turning a computer supply into a bench supply. I made one of these myself.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    That's done every day. :)
    Relays are generally pretty power-hungry, but still frequently used. SSR's (solid state relays) are quite popular.
    You can use a transistor, MOSFET, SSR, or other device.

    You could also use an appropriately rated SSR.
     
  9. CoachKalk

    Thread Starter Member

    Sep 20, 2011
    139
    2
    Thanks for the ATX Power Supply lead. I Googled it and like you said came with several good demos. I will probably not set it up like the bench supply demos because I plan to use it for this one location, but I may modify another 1 for a bench supply later - pretty handy to have around I would guess.

    As far as the end result: 12V, 5V and 3.3V supplies. If I plan to use the 12V for the sensor circuits would I still be able to use the 3.3V feed to power my lasers at the same time?

    I will also be asking for some assistance regarding what will come after my circuit. Currently I just have the buzzer sounding, but the current circuit will kill the buzzer when the laser hits the sensor again. The minimum condition I will need is for the flashing light (buzzer for now) to stay on even if the laser hits the sensor again. The fancy pants, probably out of my knowledge base setup would be to have some sort of way to "track" the number of times the flasher/buzzer was tripped (could even be a row of LED's maybe?) Any suggestions on circuits I could review or types of components to study up on would be appreciated.

    Thanks again to all of you.
    Steve
     
  10. Zod

    New Member

    Jul 3, 2011
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    0
    Google "cmos decade counter" and you have it. If it has BCD (binarily coded decimal) output, another chip will allow for driving a numeric display (seven segment LED). The TTL versions were cascadable, so I'm sure the CMOS equivalents are as well. If you only need to count to nine, then one would do. If you need to count higher, the cascaded counters are clocked off the carry pin of the prior one, and a BCD to seven segment driver will be required for each stage. If you just want to light LEDs, there was a version that clocked pins rather than having the BCD output. These were also cascadable, but past the first IC the display will have a decided binary appearance.. HTH
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Don't know how many digits you want to show, but the 4553 3-digit counter and 4543 BCD to 7-segment decoder can handle up to 3 digits at once. You can cascade more 4553/4543 pairs for more digits.

    Datasheet for the 4553:
    http://www.onsemi.com/pub_link/Collateral/MC14553B-D.PDF
    See figure 5 on page 6.
     
  12. Zod

    New Member

    Jul 3, 2011
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    And there ya go ;)
    BTW, clock for the successive stages would be the OF pin (overflow).
     
    Last edited: Sep 29, 2011
  13. CoachKalk

    Thread Starter Member

    Sep 20, 2011
    139
    2
    Thank you both. I will start looking right now at your suggestions. I can report that if the vote was held now (before tomorrow when the clean room check will take place), I would win Dad of the Year.

    I just ran a prototype run of my prototype circuit in our game room. It was extremely sensitive to floor vibrations, but what can you expect when you are balancing small mirros on Wii games, shelves and an extra mattress! Add in the intoxicating smell of 100 too many sprays of the Lysol can so the kids could see the laser lines and you can imagine the set-up.

    My middle son almost made it through until his booty caught the last beam! Now I am going to be getting pressure from them to get it "Officially Ready"!
     
  14. CoachKalk

    Thread Starter Member

    Sep 20, 2011
    139
    2
    SgtWookie - I just checked out your link. Figure 5 shows a 6 digit display and I would only need 3 (less actually, but 3 is standard with the chip(s) correct? It looks like a 4553 and 4543 are paired together for each group of 3 digits. Would I only need 1/2 of the Fig 5 circuit? Would I just shamelessly copy 1/2 of the Fig 5 circuit and forward my Pin 3 Output into all of the Vdd designations?

    Not sure about the Clock Input, Strobe and Reset references?
     
  15. Zod

    New Member

    Jul 3, 2011
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    The data sheet was showing two chips cascaded.
    You can delete the second one.
    Clock is input from your 555 circuit. Reset can be another 555 in one shot mode, pulling the line low on power up..
     
  16. Zod

    New Member

    Jul 3, 2011
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    2N3904(6?), or equivalent will do for pass transitors.
    And strobe, tie it to ground..
     
    Last edited: Sep 29, 2011
  17. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, connect them like this:

    [​IMG]
     
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  18. CoachKalk

    Thread Starter Member

    Sep 20, 2011
    139
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    Thanks Zod. I didn't understand the clock was from the 555, but it makes sense that the IC's would need their own source voltage in order to do all of that "stuff" for me.

    Could I just have a "Reset" Push Button (staight from voltage source) directly into the Reset pin to take it high? The kids would give it a go and say they get 6 strikes (laser breaks) on the dispay. Before the next attempt, a press of the reset button would take reset high and zero out the display?

    Thanks
     
  19. Zod

    New Member

    Jul 3, 2011
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    Pushbutton to ground would do, but then you have to debounce the switch ;) Ain't easy in the digital world ;)
    Well, if you held it down on power up.. ;)
    Edit, yes you could.. If it freaked you could push it again. There are many debounce circuits out there. Most quite simple.
    But a reset button on it's own MAY work..
     
    Last edited: Sep 29, 2011
  20. iONic

    AAC Fanatic!

    Nov 16, 2007
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    The Computer power supply IS overkill as you stated yourself. While it would work, it is a power hog in its own rite just like using relays when not necessary.

    Just my take on the supply issue.
     
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