555 timer Tone Generator

Discussion in 'The Projects Forum' started by DivadWaldoss, Nov 16, 2011.

  1. DivadWaldoss

    Thread Starter Member

    Nov 16, 2011
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    I'm wanting to make a tone generator with a 555 timer that is a frequency humans can't hear. I'm going to follow the schematic below. My R1 (potentiometer) will be 10k. R2 will be 33k. C1 will be .001mF. What should capacitor 2 be? And would the resistors i mentioned work for making a tone within the 17-20 Khz range? Also, how and where would I attach the power source? I'm thinking about using a 9 volt battery. Or would something else work better? I want it to be able to run for several hours straight. Thanks!
    http://www.reconnsworld.com/audio_tonegenerate.html?
    or should I use a different schematic?

    If I have this completely off please let me know and guide me in the right direction. I'm new to this and would greatly appreciate any advice you may have.
    Thanks

    EDIT- I want it to be a constant tone, not a beap. Thanks
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    That schematic has one major flaw, and it is a big one. If R1 is adjusted to 0Ω the 555 will burn up.

    I have a full set of 555 tutorials, one of them may apply for what you want...

    555 Hysteretic Oscillator

    It will easily go past human hearing. You can eliminate the LEDs, but you'll need a tweater to drive it. There was a similar thread not too long ago about a dog whistle.

    Bill's Index

    The 555 Projects

    My Cookbook
     
  3. DivadWaldoss

    Thread Starter Member

    Nov 16, 2011
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    Hey, what things would I need to change in your schematic to make it produce the high frequencies I'm wanting?
    would the numbers i listed for the capacitors/resistors work?
    Thanks
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Read the text, it gives full explanations. There are only two components in this schematic that will adjust the frequency, the resistors and the cap. The variable resistor will set whatever tone you want.

    If you want a specific frequency, such at 18Khz, the math is there too.

    As I read your request this will work right out of the box.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    It may interest you to know where your ability to hear upper frequencies drops off. It goes with your age, and might be as low as 12K or so. School kids like using a ringtone on their smartphones that teachers and other adults can't hear.

    There are free tone generators you can run on your computer, just like a hearing test. It takes a few tests to separate your own hearing loss from the abilities of your sound system.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    A tone generator driving a speaker tests the high frequency response of your hearing and of the speaker. The response from a piezo tweeter is all over the place with peaks and valleys.
    A hearing test stops at only 8kHz because if you can hear the muffled sounds from a telephone then they think your hearing is good enough. They don't care about good music.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    As far as R1 goes, I suggest that you use no less than 100 Ohms per 1V of your supply. If you're operating from 9v, then R1 needs to be at least 900 Ohms. If you go much lower than that, current through pin 7 becomes rather high when the timing cap C1 is being discharged.
     
  8. DivadWaldoss

    Thread Starter Member

    Nov 16, 2011
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    Alright, so today i went to radio shack and bought myself a little birthday present. Let me know if it'll work or if i need to buy anything else. This is what I bought:

    555CN Timer IC
    10k- Ohm Audio-Taper Potentiometer
    10k 1/4 watt 5% tolerance resistors
    10k 1/2 watt 5% tolerance resistors (accidently bought this instead of 1k...)
    33k 1/2 warr 5% tolerance resistors
    .001uF Ceramic-Disk Capacitor
    1.0uF Metalized-Film Capacitor (they didn't have 1.0uF ceramic)

    I then obviously already have a 9v battery and clip. I'm going to salvage an on/off switch from an old electronic device.
    Can I use these parts to make what I'm wanting? If I need something else, please let me know! Thanks!

    also, i didn't have enough money on me at the time to get a board to put it on... is that a big deal? It's just an added expense and if it's not that important I'll just go without it... or do i NEED one?

    Thanks everyone!
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    The protoboard lets you play with the circuit, but you can easily buy a solder type breadboard, which sounds like what you've done. This circuit is so simple you could use the dead bug method (parts glued down upside down with superglue), or point to point (no board, think 3D art). Ugly, but it works.

    The only other part that is going to be critical is the speaker itself. An off the shelf speaker will probably not hit the range you are wanting, but I've been wrong before.

    I buy from Radio Shack, but as a last resort. They have about a 300% markup on everything they sell.

    Where are you located, this helps recommend parts sources.

    555 timer dog whistle help
     
  10. DivadWaldoss

    Thread Starter Member

    Nov 16, 2011
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    I was able to salvage a switch. I have a piezo speeker from a greeting sound card.
    so i have all the parts i need?
    so following this
    http://forum.allaboutcircuits.com/attachment.php?attachmentid=13767&stc=1&d=1258895992
    i dont use R1 or R2 since i'm not using LEDS
    where does C2 go? also, how do i know which resistors of mine to use to match with your schematic?
    would it help if i took pictures of what i have with labels, and have it layed out, then maybe you could tell me what to put where, or if you're feeling extra nice (after all it is my birthday, haha) make me a simple schematic using my parts.
    I really appreciate all the help!
    Thanks!
     
  11. DivadWaldoss

    Thread Starter Member

    Nov 16, 2011
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    also,
    i used a 555 frequency calculator
    to get a pitch around 18-19 it had a bunch of different possible resistors and capacitor combos... i chose the one with a .001uF Cap... a 10k resistor, and a 33k resistor
    http://totusterra.com/555timercalc.html
    i typed .1 for the seconds ( i want a continuous tone) and 19000 for the hz... i used the specs for the 7th option down.
     
  12. DivadWaldoss

    Thread Starter Member

    Nov 16, 2011
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    0
    bump..... :D
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    OK, if you use the .001uF cap from pins 2 & 6 to ground, the 10k resistor for R1 (from Vcc to pin 7) and 33k for R2 (from pin 7 to pins 2 & 6), you should get nearly 19kHz out.

    If you use those values with Bill_Marsden's schematic (the one with R3=10k, R4=10k pot, replacing the 10k pot with a 33k fixed to pin 3) you would wind up with ~12.5kHz out. If there were just a single 33k resistor, it would be around 15.75kHz.

    I'm none too certain that your piezo "speaker" will work. They frequently "like" a certain narrow range of frequencies; what that particular one likes is anyone's guess at the moment.

    You may need to obtain a tweeter speaker that's designed to produce such high frequencies. You will also need a capacitor between pin 3 and the speaker so you won't have high DC current flow through the speaker when pin 3 is high. A 10 to 100uF electrolytic cap would probably work OK.
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    Wookie, do you think an audio transformer would help? I'm thinking of a 8Ω:600Ω for the tweeter speaker. My impression of tweeters is most of them are piezo speakers, but I'm not sure of that.

    To the OP, did you review the link I gave for the dog whistle? It falls under past art, where someone did something extremely familiar to what you were wanting to do.
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Well, the DC current would need to be blocked regardless. The 555 just has a HI/LOW output. If the piezo is connected from it to ground, or from it to +V, it won't have AC across it, it'll have pulsating DC. At some point, a transformer could saturate if the DC wasn't blocked.

    I don't know for certain whether that piezo speaker needs DC going through it or not, but if it came out of a greeting card, it was probably powered by 1.2 to 3v. Trying to run it using higher voltage may fry it immediately.
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    Extremely cheap speakers use a piezo tweeter. They have sharp null and peak frequencies and I call them a whistle, not a speaker. If you tune the frequency to one of its sensitive peak frequencies then your idea might work.

    Here is the frequency response of a typical piezo transducer:
     
    Last edited: Nov 20, 2011
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  17. SgtWookie

    Expert

    Jul 17, 2007
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    AG, you swapped colors for your nulls and peaks.
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    OOps, I corrected it. Isn't its frequency response awful?
     
  19. Wendy

    Moderator

    Mar 24, 2008
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    I really appreciated the info, which may not like sound like it with this question. If you are producing a monotone, does freq response matter as much? It may not be as efficient, but it works.

    AC coupling assumed, would an audio transformer boost the efficiency of a piezo tweeter? It seems to me it would, which would apply for the OP's project.

    I used to use 555's almost 40 years ago in college with stereo's in the U/S range. Some of the effects on people were very Twilight Zone.
     
  20. Audioguru

    New Member

    Dec 20, 2007
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    A piezo transducer has peak resonances that are loud and null frequencies that cancel so its frequency response is all over the place as I showed on a graph of its "loudness" vs frequency. It is loud only at certain very narrow frequencies then produces nearly no sound at other nearby frequencies. A smoke detector (or piezo beeper) is loud because its oscillator has positive feedback at its loudest frequency.

    The efficiency will be the same but if the voltage and power are increased by the transformer then the piezo speaker should be louder.

    Is this the thread that has a tiny piezo transducer from a greeting card? Then its max allowed power rating is very low and the higher power from a transformer will destroy it.
     
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