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Need help with a simple circuit

Discussion in 'General Electronics Discussion' started by jdkot, Oct 29, 2016.

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  1. jdkot

    jdkot

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    Oct 29, 2016
    I really know very little about electronics. I have a little basic knowledge, but not enough to figure out a simple idea. I want to build a version of the old loop and wire game. The one where you try to move the loop along the wire without touching the wire. If you touch the wire a buzzer sounds.. That I can figure out. What I really want to do is build something that when you touch the wire with the loop, it shuts off the power and you have to push some type of reset at the start with the loop hence forcing a complete start over.
    I would really like to do this powered by AA batteries if possible.
    I need help figuring out what to use, how to build it. And where to get what I would imagine is some sort of mini circuit breaker / reset.
    Appreciate any help anyone can give.
     
  2. Anon_LG

    Anon_LG

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    Jun 24, 2014
    This sounds like a reasonable first project, unlike some I have seen that want to start by making some image processing, laser-guided, PhD-experience-required marketable product. It is important to be realistic.

    What you describe can be done and should be within what you know, while teaching you something further about electronics. You may either use a prebuilt buzzer module or build you own monotone audio circuit using a 555. In terms of contacting the loop and the wire and the reset back at the start, you could use a SR flip flop for both (with set input you going to the wire and the reset input going to the reset contact) which would also sort out the problem of denouncing the contact (when the loop touches the wire it is not a clean contact there will be multiple spikes). Simply hold both the wire and the reset high using pull up resistors, and attach the loop to zero volts. And yes, you can power this off of AA's, three of them would give the voltage necessary to power the IC and likely the module.

    Do you want to go with a premade buzzer module or make your own? I can talk you through making your own if you wish, and it is not particularly complex.

    Get back to me on what you do and do not understand and I can explain further.
     
  3. jdkot

    jdkot

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    Oct 29, 2016
    Lavaguava, Thanks for the information.
    I think instead of a buzzer I would like to use a LED light instead of a buzzer. I have heard of a 555 but don't know what it is or does. I understand about the wire and the spikes, but don't understand the part about holding the wire and the reset high using pull up resistors.
    I think I need to do a little more reading. I did some reading on the SR flip flop. It will take alot more reading for me to get a handle on what it is and does. Like I said alot of reading ahead it looks like. I thought it would be simple HA HA.
    Being it was late last night I see i forgot to mention that at the other end of the wire, I would like the loop to be able to touch a switch that would open a simple lock of some sort. On the order of an electronic dead bolt. so I would imagine the loop would have to be on the positive side.
    What I am trying to build is a box with the wire and loop on the exterior that if you get to the end without touching the wire you will be able to unlock a door and claim a prize.
    Thanks again for the help.
     
  4. Anon_LG

    Anon_LG

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    Jun 24, 2014
    Ok, an LED is reasonable, and if you wish, a buzzer can be added in later if you change your mind!

    I have included below a circuit diagram for the LED part of the circuit. I will explain each part.

    Sketch300153546.png
    The lines indicate connections, in this case made with wires and a breadboard. The spots show where more than two connections join, and obviously wires going into things and 90 degree bends are connected as well. The symbol to the leftmost, two lines, one long and one short, designate a battery or cell, the long one is the + terminal and the short one is the - terminal. This means that the top most line in the diagram is connected to positive and the bottom most one is 0 volts, our reference point.

    The broad triangles here represent components that there are no symbols for, triangle A is connected to your metal loop, triangle B is connected to reset (a piece of metal is suitable for making the contact) and triangle C is connected to the wire. The two boxes are resistors, here pull up resistors. These hold the lines high, which is necessary due to the latch being an active LOW system, it is as simple as connecting the inputs to the positive voltage through a suitable resistor, here likely ~5kΩ.

    The box with S and R with lines over them and the Q with and without a line over it is an SR latch. This is how the reset of the light is implemented. These little lines can make explaining the station to beginners difficult, I have to explain the concept of active low. The way you would think of a system working would be positive being YES, TRUE etc and 0V being NO, False etc. Active low is the other way around, asystem of using a high signal (a positive voltage usually in the range of 3 to 5 volts) to represent a FALSE and a low signal (for these purposes always 0 volts or a very, very small voltage) to represent TRUE. On an SR latch if the output is TRUE then Q (the one WITHOUT the line over it) will be high. If the output is FALSE then Q will off. As the LED is connected to Q then the LED will light when the output is TRUE. The Q with the line over it is a mirror image, it will be on when Q is off and off when Q is on.

    Therefore we see that when your loop does not touch the reset of the wire, both S and R will both be high and the SR flip flop will not change state, ie if the light was on it would stay on and if it was off it would stay off. If you touch the wire with the loop then S is pulled low, this is because although the resistor makes Q high usually, it is such a high resistance compared to the metal-metal contact that it has no effect (it forms a voltage divider, but that is not important), so because it is an active low system this is taken as true, and the light turns on, regardless of the previous state. If you contact the reset, the same thing hapens, but this time with R, making Q low and turning the LED off.

    This may be a bit confusing, but is rather logical. The SR latch I am assuming is a NAND latch, one composed of NAND gates, the other variety is a NOR latch. See here for some more information of on SR latches: https://en.m.wikipedia.org/wiki/Flip-flop_(electronics)#Simple_set-reset_latches Wikipedia is as good as any for most electronics research.

    I suggest you do some research on the things I have said and it should make sense, I found the concept of a pull up/pull down resistor confusing, but you will need to be familiar with the concept t some point.

    The lock can be done in several ways, it really depends on what kind of lock. I would suggest a spring loaded solenoid that catches on the inside of your box. But that is the next step after the above.

    Apologies for the diagram quality I am on a tablet and the moment and there is no convenient software for drawing circuit diagrams.
     
    Arouse1973 likes this.
  5. AnalogKid

    AnalogKid

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    Jun 10, 2015
    There are many different technologies that can be used to do what you want: a relay, a logic gate chip, a pre-packaged flipflop logic chip, or two transistors plus some resistors. What parts do you have, and what parts are you comfortable using?

    Also, are AA batteries a requirement, or is a single 9 V transistor radio battery ok?

    ak
     
  6. jdkot

    jdkot

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    Oct 29, 2016
    Thank you for the diagram. Just got a chance to look at it. Now I need to research some of what you said... and I thought it would be a simple project...:D:eek:;). How does one determine the value of the resistors? and where do you go to buy these things? I think all our Radio Shacks in this area are long gone.
    I am anxious to figure this all out and actually try to build it. Between remodeling the house (making it all wheelchair accessible) and the other chores, I am going to sneak in a little time to do some study on this. Thanks again.
     
    Anon_LG likes this.
  7. jdkot

    jdkot

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    Oct 29, 2016
    AA would be best for the application, but 9 volt would also work. Once up and running the user would need to supply their own battery, and I figure AA would be more commonly available. I would eventually want to use this in a geocache once I figure out how to build it and a case to hold it.
    I don't have any parts at the moment. This is a completely new field for me. I have used resistors with some LED applications, but those are the only things I would have laying around. A logic gate chip, a prepackaged flipflop logic chip, or two transistors plus some resistors are all things I am unfamiliar with at the moment. So this is not only a build, but it is a learning session for me. Something I have had an interest in, but no time until now to actually delve into it.
     
    Last edited: Nov 1, 2016
  8. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Where are you located?

    Before we get to circuit design, let's do a little product design:
    How many LEDs, what are their colors, what are their functions?
    How do you restart the game if you bump the wire?
    What is the unlock mechanism. The circuit and 1 or 2 LEDs is a very low power device, but the unlock motor or solenoid might need much more power (briefly). this affects the choice of batteries and the output driver parts.
    Will the finished device have an on-off switch, of can it sit in a very low power mode waiting for someone to play?

    Once you nail down what you want it to do, how you want it to 'think', the circuit is pretty easy.

    ak
     
    Last edited: Nov 1, 2016
  9. jdkot

    jdkot

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    Oct 29, 2016
    Sorry for the delay getting back to you. Busy with the remodel.
    I just want a couple of LEDs. Red, white, green color really doesn't matter though red would probably be ideal. To restart the game I would like to have it so that the wand had to be brought back to the starting point and push a reset button with it. The unlock mechanism I figured would probably be a magnetic lock I had not given it much thought as of yet. I probably should considering it is a integral part of circuit I thought that the lock mechanism could have its own power source and just be triggered. I haven't thought that one through entirely. I live in the area of Tacoma Wa. Not sure where to look for the parts yet.
     
  10. BobK

    BobK

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    Jan 5, 2010
    Most parts are purchased online now (like everything else.)

    Bob
     
  11. Anon_LG

    Anon_LG

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    Jun 24, 2014
    Sorry for not replying for a while, very busy with homework. Good luck with the research, which will be necessary to learn about the general operation of the components. Of course more specific questions can be answered here. In terms of obtaining the parts, I use Maplin (a physical store), but unfortunately it sounds like you are in America, not England. For international suppliers you could go with Mouser, Digikey or Element 14, all of which are commended by various electronics books and Youtube channels. So as BobK said, online would be your best option.

    You may want to purchase a good book on the subject, without one you will be going through disparate information scattered online. I would recommend electronics for dummies, it teaches the basics of electronics and should get you up to the level required to complete this project.
     
  12. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    You just need an SCR[​IMG]
     
    duke37 and jdkot like this.
  13. jdkot

    jdkot

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    1
    Oct 29, 2016
    Colin, Thanks for the diagram, I actually understand some of it...lol... Got to look at this for awhile. See if I can make sense out of it in my mind. What / where do I find a reset button that would work in this? And a electronic lock, like a door lock. how would that fit in?
     
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