Newbie needs help with 4093 relaxation oscillator?

Discussion in 'The Projects Forum' started by misha680, Oct 9, 2008.

  1. misha680

    Thread Starter Member

    Oct 9, 2008
    15
    0
    Hi,

    I am pretty much an electronics newbie. Some soldering experience now and I did take an E&M class in college (physics intense version, highly theoretical, like you know derive special relativity from Maxwell's laws and vice versa not something that would help here).

    I am trying to make this:
    http://www.roombareview.com/chat/viewtopic.php?p=6029#6029

    From what I understand, it is a relaxation oscillator (?) that makes a 500Hz pulse modulated on a 35Khz carrier pulse using a 4093 quad schmitt-trigger chip. I am trying to figure out how to calculate/change frequencies based on resistance and capacitance values for something like this. I found something for a much simpler circuit, but nothing with a 4093. Any suggestions/help/leads?

    Thanks a bunch.

    Misha
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Hello Misha,
    Have you downloaded any datasheets from the manufacturers of the IC's that you are trying to use?

    Basically, it's an RC time constant. Feedback to the input is R, with the C on the input being charged by the feedback R.

    Have a look at a few datasheets for details.

    ONsemi, Fairchild, etc.
    MC14093B, CD4093B, etc.
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    In case you are unfamiliar with where to locate the manufacturer's datasheet for the part in question, here is a link to the CD4093B datasheet on the National Semiconductor website.

    hgmjr
     
  4. misha680

    Thread Starter Member

    Oct 9, 2008
    15
    0
    Thank you both for the datasheet idea. I will check out it and let you know if I have any more questions.

    Thanks again
    Misha
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The CD4093 cannot properly drive the 220 ohm resistor when its supply voltage is only 5V. 10k is the recommended minimum value.

    Change the 220 ohm resistor to 10k, and change the the 22k resistor to 1M.

    Then the capacitors can be changed as well. Change the capacitors to 2.2nf.
     
  6. misha680

    Thread Starter Member

    Oct 9, 2008
    15
    0
    Thanks for the replies guys. Btw, what wattage resistors do I need to use for the circuit (1/4, 1/2, 1, 2) and how do I figure this out?

    Thanks
    Misha
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    1/4 watt will give enough dissipation. Power dissipated in a resistor is the product of the voltage drop across it times the current through it.

    Rule of thumb: if the resistor gets dark and stinks, then you need a larger one.
     
  8. misha680

    Thread Starter Member

    Oct 9, 2008
    15
    0
    Btw is there an instrument I can use to test the frequency of the signal I am producing? I believe I can use an oscilloscope but I mean one that would be fairly easily available to me without spending a lot of money. Or some trick I could use? Perhaps another circuit?

    Thank you
    Misha
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    A frequency counter is used to accurately measure frequency. My Fluke multimeter measures frequencies accurately up to 200kHz.
     
  10. misha680

    Thread Starter Member

    Oct 9, 2008
    15
    0
    So it looks like I have to finally make the multimeter plunge (I've avoided owning one at least for more than a few days - buy/return from Radio Shack). Fluke's look pretty pricey, I know they are the industry standard but still I don't really think I would like to spend that much.

    It seems like there are some decent prices on Amprobe's, something like this:
    http://www.tooldiscounter.com/ItemDisplay.cfm?lookup=AMPPM51A&source=froogle&kw=AMPPM51A

    Also futurelec has really low prices, not sure of brand:
    http://www.futurlec.com/Multimeters.shtml

    And finally I found this guide, but not sure how recent/dated it is (esp w/regards to Amprobe):
    http://www.tangentsoft.net/elec/meters.html

    Any advice? I'd like something that's ideally not too expensive (I am really thinking the less the better but I mean $30-40 range at least is "ok", $50 is pushing it if there is _really_ something I can't live without). I'd like something that will be good for occasional hobby use (I do my hobby electronics stuff only on weekends basically and then only a few hours a weekend usually if that) but that will have the most capabilities so I won't have to look for something else (frequency obviously, capacitance and diodes I guess are nice, not sure what else)... Any advice would be greatly appreciated.

    Thank you
    Misha
     
  11. misha680

    Thread Starter Member

    Oct 9, 2008
    15
    0
  12. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The Amprobe multimeter might be a good one.
     
  13. misha680

    Thread Starter Member

    Oct 9, 2008
    15
    0
    Thanks. Just got it this morning.

    Misha
     
  14. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    That could also mean something is shorted! LoL ;)
     
  15. Capt-Killjoy

    Active Member

    Sep 29, 2008
    58
    0
    Personally, I would go the longer dollar and get yourself a nice Fluke. I have tried different meters over the years, but Fluke meters are accurate, dependable, and take a pounding without crapping out on you after an accidental fall. You can get them in all kinds of various configurations. I found it best to make a list of all the things I wanted my meter to be able to do (now and in the future) and get one that fits that ticket. Better to spend a little more once, than to have to keep re-buying until you get what you want. And if you are going to keep experimenting with electronics, you will need a good meter.
     
  16. misha680

    Thread Starter Member

    Oct 9, 2008
    15
    0
    Thanks guys for all the help. The fluke's were 100's of $$$ and I am a student... The Amprobe is nice though and much better than nothing or Radio Shack.

    I am assuming the 500 Hz being modulated should be the frequency on output 3 of CD4093BCN compared to 0V anywhere from power supply, and the carrier frequency 35 KHz should be the frequency measured on output 4 of CD4093BCN.

    With the original circuit I get 421 Hz on output 3 and 3.36 KHz on output 4. If I make the replacements Audioguru suggested (thank you) I get 450 Hz on 3 and 27.4 KHz on output 4. Apparently the 37.5 is quite critical though. Any suggestions? I might try something like the first post at top of:

    http://www.roombareview.com/chat/viewtopic.php?t=1178&postdays=0&postorder=asc&start=20

    to see if that helps tomorrow if I don't hear any other suggestions then. Don't know, can't hurt, play with potentiometer see what I end up adjusting. I'm pretty new at this still, but having the multimeter definitely helps a lot.

    Thank you
    Misha

    p.s. I included a picture of the circuit I built so far (original spec version). I believe it is correctly assembled per spec. Also, I put dots where I am putting leads to measure frequencies above, I believe it is correct places let me know otherwise. The black dot is where the black lead is for both measurements (I tried flipping leads too but it doesn't make difference), the two red dots are the two frequencies I report above. Thanks for all your comments guys.

    http://www.google.com/search?q=cd40...=com.ubuntu:en-US:unofficial&client=firefox-a[​IMG]
     
  17. misha680

    Thread Starter Member

    Oct 9, 2008
    15
    0
    Bump. Umm, help? I did some calculations based on spec sheet, and my measured values don't seem to make sense, even if I make no assumptions about the V+/V- levels and just assume they are the same from the first input to the second and try plugging in the RC values. Am I measuring in the wrong places or could something else be going on? Thanks
     
  18. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Try measuring pin 11 to ground.
     
  19. misha680

    Thread Starter Member

    Oct 9, 2008
    15
    0
    You mean for frequency or voltage?

    Thanks
    Misha
     
  20. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Frequency.
     
Loading...