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Wiring a small circuit

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  • 24-10-2011 7:09pm
    #1
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭


    I'm very new to circuits but I started on a project not long ago and I now have all the components ready or on the way. The last thing I'm stuck on is wiring. Where can I get very small wires suitable for a small LED circuit, or does it matter if I just cut apart an old A/V cable?


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    #2
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    You could use matrix board you can get in maplin, it has copper strips on it with holes in it, to solder components onto. You cut the copper trackes in places to suit the circuit being made.

    Or you could get a small solderless breadboard that you can plug the components into, along with link wires you get for them. Circuits can be put together on them and changed easily as you go along.


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    #3
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    Hi, thanks

    Sorry, I should have mentioned that I'm not using a circuit board in this. Just looking for some sort of insulated wire to carry the current of about 20-25 mA. I'm just not sure if there are specific types of wires or where to get them, would say Woodies diy do it?


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    #4
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Cian A wrote: »
    Hi, thanks

    Sorry, I should have mentioned that I'm not using a circuit board in this. Just looking for some sort of insulated wire to carry the current of about 20-25 mA. I'm just not sure if there are specific types of wires or where to get them, would say Woodies diy do it?

    I sometimes use strands from alarm cable for that type of thing, i etch out circuit boards sometimes, or use the matrix board, so not much wiring is needed but small links i would make with the alarm cable cores anyway.

    Have used cat5 strands as well, but the alarm cable cores are more flexible.


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    #5
    DublinDilbert
    Registered Users Posts: 5,379 ✭✭✭DublinDilbert


    Yea cut up an old cat5 patch cable, it's not the worst to work with. You could use pretty much anything, an old av cable like you said, an old USB cable ect....


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    #6
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    Ok so I exposed on old Av cable, There was another tube inside of that which I just left alone and then took the Copper strands, twisted them and tested them on a remote control and battery which worked alright.

    So should this cable be able to carry a smallish current alright?


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    #7
    Stoner
    Registered Users Posts: 10,952 ✭✭✭✭Stoner


    it would be best to take a cable that was insulated, have you made a cable by twisting strands? was the other tube you took of the insulation? the cables used on some headphone AV cables can carry a small current, but nothing much. to be exact wed need to know the cross sectional area of the cable and its lenght, but if you are just making a small circuit fed from a battery something the size of a single core alarm cable as mentioned above is fine, or CAT5, but it would not want to be thinner than that.


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    #8
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    This is what a google returned https://audiohut.co.uk/shop/product_info.php?manufacturers_id=4&products_id=7150&osCsid=oltckvtvfh2ajn4cfbru168if5

    The Voltage supplied is 9v and current 20-25mA, I'm powering 11 LED's with 5x2 and a single in Parallel and 6 resistors.

    9v - 120o resistor - 3.1v led - 3.1v led (x5)
    ---- 270o resistor - 3.1v led


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    #9
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    With led`s with forward voltage of 3.1, they wont light to full brightness if you put 5 in series with the 9v battery, if at all.

    You could connect 2 in series with a 150R resistor, and have 5 of these 2 series ones in parallel, and the single one with a 330R resistor.

    Or do it the way you were going to, but with 2 x 9v batteries in series, the same 120 resistor will do for the 5 in series, and an 820R resistor for the single one.

    You could probably connect 3 in series direct to the 9v battery also, without any resistor. That would be 3 x 3 and then 2 with the 120 resistor.

    The resistor needed anyway can be got from R = (Vs-Vl)/I
    Vs = supply (9v for you)
    Vl = led forward voltage (3.1)
    I = led current (0.02A) or 20 mA

    So if you put 2 in series its R = (9-6.2)/0.02 = 140 ohm. Ideally, a 150R resistor should be used, as its the nearest higher value, but the 120 should be ok also.

    Notice the Vl was 6.2v. Thats because you now have 2 led`s in series, so the Vl (led forward voltage) is 2 x 3.1. If you had 5 in series, this would be 15.5v for 5 x 3.1v led`s in series, which is why 2 of the 9v batteries in series would be needed for that setup to work properly.

    I was thinking the same as stoner when you mentioned using the AV cable outer ground conductor, you definitely want some insulated strands. Id still say a bit of alarm cable, or a bit of telephone extension cable.
    Something like this could be cut up and would do fine. its quite delicate stripping small wires without cutting the conductor, but should be ok.

    Why do it all without any circuit board? Are you going to mount the components on anything?

    Edit: Looking again, maybe you meant 5 sets of 2 leds in series anyway.


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    #10
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    robbie7730 wrote: »
    With led`s with forward voltage of 3.1, they wont light to full brightness if you put 5 in series with the 9v battery, if at all.

    You could connect 2 in series with a 150R resistor, and have 5 of these 2 series ones in parallel, and the single one with a 330R resistor.

    Or do it the way you were going to, but with 2 x 9v batteries in series, the same 120 resistor will do for the 5 in series, and an 820R resistor for the single one.

    You could probably connect 3 in series direct to the 9v battery also, without any resistor. That would be 3 x 3 and then 2 with the 120 resistor.

    The resistor needed anyway can be got from R = (Vs-Vl)/I
    Vs = supply (9v for you)
    Vl = led forward voltage (3.1)
    I = led current (0.02A) or 20 mA

    So if you put 2 in series its R = (9-6.2)/0.02 = 140 ohm. Ideally, a 150R resistor should be used, as its the nearest higher value, but the 120 should be ok also.

    Notice the Vl was 6.2v. Thats because you now have 2 led`s in series, so the Vl (led forward voltage) is 2 x 3.1. If you had 5 in series, this would be 15.5v for 5 x 3.1v led`s in series, which is why 2 of the 9v batteries in series would be needed for that setup to work properly.

    I was thinking the same as stoner when you mentioned using the AV cable outer ground conductor, you definitely want some insulated strands. Id still say a bit of alarm cable, or a bit of telephone extension cable.
    Something like this could be cut up and would do fine. its quite delicate stripping small wires without cutting the conductor, but should be ok.

    Why do it all without any circuit board? Are you going to mount the components on anything?

    Edit: Looking again, maybe you meant 5 sets of 2 leds in series anyway.

    Yes sorry my bad I didn't make that clear I meant 5 parallel sets of 2 leds and 1 resistor in series (and a single led and resistor in parallel also).

    With regards to the resistors, would it matter if the resistance was slightly lower as I think the leds can tolerate 20-30mA?

    Thanks for the advice on the cable.


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    #11
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Cian A wrote: »
    With regards to the resistors, would it matter if the resistance was slightly lower as I think the leds can tolerate 20-30mA?
    Yes they should be ok. Id say it will be better to have a 120R resistor for each set of 2 led`s too.


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    #12
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    robbie7730 wrote: »
    Yes they should be ok. Id say it will be better to have a 120R resistor for each set of 2 led`s too.

    I had planned on that, I presume you are speaking of a 120r before the circuit splits, I hadn't thought of that but obviously enough now it wouldn't have been a good idea anyway.

    I should have the rest of my components tomorrow or thursday, can't wait to start:D.


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    #13
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Well what i mean is each 2 led`s in series will likely work better with their own resistor of 120 ohms. And the single one on its own then with another resistor of 330 ohms.

    If you use a single resistor for the 5 legs of 2 leds in series, a 28 ohm resistor will be needed rather than the 120R one that would be needed for a single leg of 2 leds in series. So its 5 seperate 120 ohm resistors, or a single 28 ohm one.


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    #14
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Cian A wrote: »
    I should have the rest of my components tomorrow or thursday, can't wait to start:D.

    Its interesting alright, i used to do a bit with the electronics years ago, then did some in a real project this time last year, and doing a couple of projects now to get back into it.


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