Shahriar Posted August 7, 2005 Report Posted August 7, 2005 HiI have build an square wave oscillator with LM324(which is a quad opAmp).I have connected the output to a TIP122(power Transistor) and drive a piezo to creata beep sound. but the interesting problem: There is a VIZZ in the output sound. when I touch the Vcc or GND or some other points of the circuit, the vizz will dissapear. When i make the square wave with a NE555 there is no VIZZ and everything is OK. I don't think itis because of noise!!! I connected so many points with a Resistor or capacitor to ground or put some capacitors between Vcc and Ground but nothing special. I have used one of the opAmps from 4 opAmps of LM324, when I touch the floating inputs nothing happen but when I touch the floating outputs the vizz will dissapear.Few month ago the same thing happened when I built a preAmplifier with NE5532. there was a small Vizz in the Output which would dissapear when Itouched the GND. P.S. I have used a speaker choke to drive te piezo. I hope you understood what i meant by a piezo. it is something like a coin and when connected toa oscillator it sounds like a buzzer. I do not know the exact english name!!!ThanX in advanceShahriar Quote
Guest Alun Posted August 7, 2005 Report Posted August 7, 2005 Could you post a schematic?What do you want to achieve with this circuit?If it's just a continuous tone I'd recommend a piezo buzzer. Quote
Shahriar Posted August 9, 2005 Author Report Posted August 9, 2005 Dear AlunThe circuit is to creat a loud Beep. small buzzers can not creat such a loud sound.when I used a coupling capacitor between the output of opAmp and the transistor Base, the effect of my hand dissapeared, then I remembered that the PreAmplifier I had build, was a DC coupling PreAmplifier (it did,'t have any coupling capacitor). But the thing I didn't understand was the effect of my Hand!!!!!!!!!Anyway, I changed the circuit and build a sinewave oscillator with opamp and there is no Vizz with or without a coupling cap. ???but the question still remains: What is the effect of Hand???ThanX Shahriar Quote
audioguru Posted August 9, 2005 Report Posted August 9, 2005 Hi Shahriar,I think that the VIZZ was your circuit oscillating at a very high frequency. Your hand on its ground stopped the oscillation.An oscilloscope would show the problem and what your hand is doing to it. ;D Quote
Shahriar Posted August 11, 2005 Author Report Posted August 11, 2005 Yeah, It can be a possible.I will check it and tell you.Thank you very muchShahriar Quote
konsempu Posted September 26, 2005 Report Posted September 26, 2005 can you teach me how to make an improvised buzzer plz?? its our project anf i have no idea about doing this . Plz. Quote
Shahriar Posted September 27, 2005 Author Report Posted September 27, 2005 Dear konsempu This is the schematic I used. I omitted the parts which you didn't need, {Beacuse I was building a Fishing Buzzer}The schematic you see is just the Buzzer. the Left part is an Sine-Wave Oscillator the right part is the driver. the transformer is a simple Audio transformer. it is there to increase the voltage. you can pull down the base of the transistor with a pot to control the volume. Becarefull the transistor not to get too much Hot. you can use power transistors.hth - Shahriar Quote
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