Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

AC on breadboard

  1. Mar 4, 2013 #1
    I was wanting to get some hands on experience with AC current circuits. I have been tinkering with DC circuits on a breadboard and was wondering what the best way to get AC on a breadboard would be. I can't really spend 200+ on a function generator. I might spend 30 or so on a kit function generator if that is what I need. I also of course can't buy an oscilloscope.

    So my question I suppose is, is a kit function generator worth it for an amateur hobbyist?

    And, why can't I just mimic AC using oscillating circuits of some sort?

    Thanks.
     
  2. jcsd
  3. Mar 4, 2013 #2
    I just posted something like this the other day - look to a PC Soundcard solution like: http://www.zeitnitz.de/Christian/scope_en - I have not used this product and there are android scopes / signal gens as well - but for the $.... this has to be what you are looking for.
     
  4. Mar 4, 2013 #3
    Getting a function generator would be useless without an oscilloscope. I'm in the same position as you. I still don't have these two equipments because I think that I don't need them that much at this level, although I'm a fourth year engineering student, but I get away with this problem by using PSpice simulation software. Testing different concepts, theories and some applications with this incredible software, is really entertaining.
     
  5. Mar 4, 2013 #4
    Out of curiosity, a year ago or so I downloaded the zeitnitz soundcard scope that Windadct suggested. It is pretty impressive for a freebie (although I have no practical use for it). Basically an audio frequency scope.

    For a source you can use your IPhone. It contains an app for driving an audio sinewave out to headset port.

    So, If you have an IPhone and a PC, you have everything you need for free.
     
  6. Mar 4, 2013 #5

    davenn

    User Avatar
    Science Advisor
    Gold Member

    yeah simulations are ok sorta ... problem is most of them assume ideal conditions
    there's nothing like building an actual circuit and measuring the results with real test gear
    where real world components have wide and varied tolerances that add a whole different effect to the operation of the circuit being experimented with

    Dave
     
  7. Mar 5, 2013 #6

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    I found this link It could be a way in for you. It's a fairly straightforward thing to do and there are a number of freebies that will give you a scope picture and allow you to source low frequency (audio) signals with a PC.
     
  8. Mar 9, 2013 #7
    sophiecentaur,

    I have the cable to try this, but I don't have a line-in jack on my laptop.

    Would this work with a mic jack? I guess not since its just mono.

    Otherwise I might have to buy an external usb sound card.
     
  9. Mar 9, 2013 #8

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    The mic input jack should work just as well. You may need to adjust the gain with the control panel. The only problem with using the PC is that you will have a low(ish) input impedance compared with the 1MOhm or 10MOhm of a 'scope and also a lower sensitivity. Not a problem for what you need, I think.
     
  10. Mar 9, 2013 #9
    I think I got it going, but am not sure:

    There ended up being a way to switch the mic input to a stereo mix using windows and also the software that came with my sound card drivers. I verified it was stereo after putting this together.

    So, first I stripped the stereo extension cable and found 2 wires in a copper sheath (I was expecting 3 wires). The sheath was ground. It was easy to verify the other wire connections to the 3.5 plug using my multimeter.

    Instead of soldering immediately, I decided to just build the voltage dividers on my breadboard, so I could play around with resistor values. I wanted to make sure I wasn't going over the limit for my netbook (ASUS 1000he). The other site referenced above by Windadct suggested 0.7 so I went with that. I was using a 9V (which was actually closer to 7V) and so ended up with resistors of 10k and 1k.

    I attached the wires from the stereo cable to the voltage dividers on my breadboard using alligator clips. Then for the "probe leads" I just used some jumper wires.

    I then built an astable 555 timer leading into an LED. My RC components affecting the flash frequency were 33uF and 10k ohms. I put one lead of the probe next to the anode of the LED and the other on pin 1 of the 555.

    I plugged the stereo cable into my computer and set up goldwave to start recording. As soon as I powered my circuit I got quite a surprise! My computer made the same sound as if I had connected an 8ohm loudspeaker to my circuit where the LED is. That makes sense, but still it was somewhat shocking. This however was with different RC values, when I changed to the ones mentioned above it became inaudible, but I could still hear small clicking that matched my LED lighting.

    I printed the screen to show you.

    wave.jpg

    I'm not really sure this is as it should be, especially the huge spikes. My digital multimeter seems to max around 0.5, is it as simple as the vertical axis in goldwave being voltage?

    I would be very grateful if someone could build the same circuit and test with a real oscilloscope. I will draw my circuit in circuitlab and post later.
     
  11. Mar 9, 2013 #10
    Here is a zoomed in view for a 1 second interval.

    wave2.jpg
     
  12. Mar 9, 2013 #11
    Ok, here is where that wave is supposedly coming from. And only while I was making this did I realize connecting channel B to pin 1 wasn't exactly what I wanted to do. Regardless, can anyone show me a real oscilloscope's output to compare?

    circuit.png
     
  13. Mar 9, 2013 #12
  14. Mar 24, 2013 #13
    I wanted to share some more if anyone is interested. I moved the probe voltage dividers off the breadboard and onto a terminal block to make it more convenient to use. I'm still hesitant to solder it together because I'm not really sure on the values I'm using, I always check with the multimeter first before slamming it into my computer.

    Heres some pics, the circuit is just some potentiometers and a PUT making an LED blink. Goldwave recordings have time stamps so I can see exactly how much is between blinks. The loose grey wire in the second pic is the unconnected positive for the battery.

    DSCF1544.jpg
    DSCF1545.jpg
    DSCF1547.jpg
    DSCF1548.jpg

    The yellow is ground and green channel A on the probe. I'm going to put a stranded wire across the terminal strip and do another voltage divider on the opposite side if I ever need channel B.

    I'm still not really convinced this is doing what an oscilloscope would. All I can say for sure is that I'm throwing voltage pulses through my soundcard with no noticeable damage to my computer.
     
  15. Mar 26, 2013 #14

    eq1

    User Avatar

    Nice job mishma! This is some great hacking. All those plots look AC coupled to me which is why they likely look a little different then what you are expecting. Basically, your "scope" is measuring the derivative of the input signal. I think this is likely because you are using the microphone input. I know the microphone input on my laptop is AC coupled. I suspect yours is as well.

    Apparently some laptops have a DC coupling mode on the mic input, like the OLPC kit. So you might check that.
    http://laptop.org/en/laptop/hardware/specs.shtml
     
  16. Mar 26, 2013 #15

    Integral

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Some questions for you:

    You have 2 resistors in series and are calling it a voltage divider. You are then connecting your probe to what I would call the input to the divider? Where is your signal input? As it now stands you could replace the 2 series resisters with 1 equivalent. How familiar are you with voltage dividers?

    What is IC2? If I were to attempt to recreate what you have done I need that info.
     
  17. Mar 26, 2013 #16
    Hi Integral, the resistors aren't in series, although I admit it does appear that way. If you look closely at the second to the last pic, you can see on the left side of my terminal strip there is a copper wire, a white wire, and a red wire in that order leading downwards from the top.

    The copper wire goes to ground on the input jack.

    The white wire is unconnected right now, but could be used for a second "channel" later. It goes to the middle section of my jack.

    The red is connected to the point where the two resistors meet. There is a small cylindrical metal tube stretching across it and you can screw 2 wires in from either side to connect them. So the 2 resistors are connected to the red wire. That's how it makes a voltage divider. Red leads to the tip of the jack and is having its behavior recorded in green in the pics. I will get a better picture of the terminal strip when I get home.

    The point of doing a voltage divider at all, as I understand it, is because mic inputs on laptops were only designed to handle 0.7 V or so. So I have to step it down before putting it in. That breadboard circuit is being powered by a 9V battery. I couldn't tell you how a real oscilloscope probe is designed to handle a similar circumstance, I assume the voltage limitation is something ridiculously high.

    IC2 is a 555 timer. I mentioned that in the post text but omitted it in the pic, sorry.

    eq1, looks like I will have to read up on that, thank you! I need to just break down and fix my old tower which has a decent sound-card with line-in, if that's the case.
     
  18. Mar 26, 2013 #17
    Here's what I was trying to say, Integral: on terminal strips connections aren't only made by putting wires into the same hole, but there is a connection through the strip. So the resistors are in one hole together but there is a third (red wire) that completes the node. On the second image below, red lines are drawn across the strip to indicate connections.

    connections.jpg
    connectionsmap.jpg
    holes.jpg
     
  19. Mar 27, 2013 #18

    eq1

    User Avatar

    Depending on what's wrong with the tower a cheaper option might be a USB ADC kit, a.k.a. a DSO (digital sampling oscilloscope). For $30 you can get a 2 channel 8Ksps USB kit on Ebay. http://compare.ebay.com/like/110833685985?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar [Broken]

    There are tons of other options if you're willing to spend more.
     
    Last edited by a moderator: May 6, 2017
  20. Mar 27, 2013 #19

    Integral

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I have used that connector, so am familiar with it,. Thanks for pics. but I would rather have a schematic drawing of the connection.

    What waveform do you expect from that configuration of the 555?

    Looks like it will not be straight forward, I would recommend that you wire up a simple multivariator circuit with a frequency of ~1kHz, this would be well within your PCscope capabilities and you will learn if your connection is working the way you think it is.
     
  21. Mar 27, 2013 #20
    Integral, there is a webpage referenced by sophiecentaur earlier that I am using. You can find a schematic there as well as more information. The only difference is I am using 10k and 1k for my resistor values instead of 18k and 82k as shown there. Here is the link again:

    http://www.ledametrix.com/oscope/index.html

    I will certainly try the circuit you suggest, thank you.

    eq1, you're right, I should probably just step up to something like that at this point. I haven't found any further information about my mic jack for my laptop model. This has been fun to mess with though.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: AC on breadboard
  1. LED on a breadboard (Replies: 5)

  2. Breadboard modeling (Replies: 1)

Loading...