Current Activated Buzzer Circuit Advise 1

[rocksolidsr]

I'm trying to have a buzzer beep when current is applied to a transformer, spec sheet attached. I have an idea of what I would do I just want to run it by you guys and see what you think

I was thinking of using one of these current sensors

http://search.digikey.com/scripts/d...wt.mc_id=Dxn_US_T091_Catlink;name=398-1000-ND

and run the output wire through it and use the output of that to run this circuit to make the buzzer beep.

http://www.doctronics.co.uk/555.htm#pb_04

for my buzzer circuit i used an NPN transistor and a 5v buzzer and that works fine when a voltage of 2.5V or greater is applied, I'm just not sure how to trigger it.

Do you think this would work, the output of the transducer is high voltage, high frequency >20khz


Ok I measured the output of the transducer using this current probe

http://www.aemc.com/products/pdf/1201.51.pdf

here is what i got with the probe set to 100mA/V
Cyc RMS = 472mV
Rise Time = 14.84us
Fall Time = 18.20us
Pos Width = 24.7us
Neg Width = 24.20us
Freq = 20.45kHz
Period = 48.90us
Mean = 68.7mV
Pk-Pk = 1.54V

so from those measurements I am seeing that I would probably need to measure current up to 154mA?

i'm kinda stumped here, i'm trying not to mess with the original circuit if at all possible, what is the easiest way to detect output from the transformer and have that output a voltage signal of at least 2.5V

I have the buzzer circuit working with a 555 timer and a npn transistor but i'm not sure how to only activate it when there is output from the transformer

any help would be greatly appreciated thanks.
attached is the transformers spec sheet

 

[rocksolidsr]

so this is the circuit that i have, V1 is the AC source from the current sensing transducer and V2 is a 5VDC voltage source. this drives the buzzer but it is so quiet you can barley hear it, so i'm not sure if there just isn't enough current to saturate the transistor to turn it on or what...

anyone have any ideas, thanks

 

[OperaHouse]

That should be enough to saturate Q1. I would drive the base with a 2.2K resistor in series.

Could the problem be the sound transducer is a piezo? That would give really low output. Put a 470 ohm resistor across it and see of you get sound then. We (not my design) were driving these with two gates to get about 20V PP and a pot to adjust to resonance. These were driven so hard that they were failing in the field. Got out my microscope and the wires were cracking from fatigue.

 

[OperaHouse]

I didn't look too hard at the 555 circuit. Just thought this was another 555 oscillator and you were driving a transducer that was basically a capacitor. I went back to it to make a suggestion of how to double the voltage to the transducer. That's when I noticed the 555 wouldn't oscillate. Just why is it there? In any case it is a bad idea to drive two transistors in series. Q2 should operate directly off the 5V supply.

 

[GonzaloEE]

A tone decoder like LM567 might help, tuned to the switching frequency. They have high gain and open-collector output, so you can couple the voltage through a small cap.

http://www.nteinc.com/specs/800to899/pdf/nte832.pdf

Cheers,
G

 

[rocksolidsr]

Operahouse I'm not sure what you mean by operating Q2 off of the 5V directly

anyways here is another picture of something i'm trying
i'm using a bridge rectifier to convert the ac to dc. when i measure the output voltage from the rectifier i'm getting over 100V but if i add a LED the voltage drops down to below 1V and the LED doesn't stay lit it flickers

any ideas??

 

[rocksolidsr]

Ok so I'm taking a different approach, I took my small signal and ran it through a LM741 op amp, using a +-12V supply and it worked, schematic below.

However that was just a test to see if it would work, now I need to figure out how to power the op amp with just a single supply of either 5V, 14V, or 24V. I tried using the 24V supply and using a voltage divider to create a virtual ground but when I do that I get -21V, and like 2.5V which is strange, schematic below

 

[zappedagain]

The voltage offset is due to more current flowing through R6 than through R5, about 10x more. If you want to have this passive technique working you need to use very low values of R5 and R6, so the current flowing through them is about 10x the amount of current flowing through the rest of the circuit, so the current flow from the circuit only gives about 10% error. This is a very inefficient voltage regulation technique. A first step may be to reduce your R5 and R6 resistance values by 100x, if that doesn't dissipate too much current.

A second approach is to use two 9V regulators (you need to leave some overhead for the regulators to work); this will still be a bit tricky though.

John D

 

[rocksolidsr]

So I'm trying to use a single supply op amp TLC081 i have the following circuit setup

here is the output of both the current sensor and of the opamp i just can seem to get enough output to turn on the transistor any ideas

CH2 = Output of current sensor input to opamp
CH3 = output of opamp

the current sensor i'm using is CSI-0100

http://www.inductech.com/current_sensing_transformers/current_sensing_csi0T.htm

 

[rocksolidsr]

So I think I know why I'm not getting a very good output from my op amp and that is because the signal I'm getting is being pulsed so it isn't ON the whole time, it is ON 32ms and OFF 32ms is there a way to get a constant signal from that somehow??

 

[MacGyverS2000]

flip-flop and a cap...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[rocksolidsr]

I've never used a flip flop before so i'm not sure what type to use or how i would hook it up any insight into that.

thanks

 

[MacGyverS2000]

How can someone be comfortable working with op-amps and never seen a flip-flop before (or at least be able to figure one out)? <scratch head>

Dan - Owner

http://www.Hi-TecDesigns.com

 

[OperaHouse]

Please excuse my absence. I'm on an extended vacation at my remote cabin. The beer is cooled by solar power and depending on the sun that can be from lukewarm to a slushy. I could design a controller but it is far easier to just drink them before they freeze. Back to your problem.

I suggest the following attached circuit using an open collector LM339 op amp. D1 provides a reference voltage of .6 volt. Above that, the open collector of A1 discharges the 1uF cap. 2.2K resistor can be inserted if a random pulse is a problem. The second comparator is made from the remaining three op amps to provide generous current sinking. Switching at 1/3 supply voltage provides some time delay. Reversing the two resistors could provide a better delay.

 

[OperaHouse]

See if it loaded this time.

 

[rocksolidsr]

i will give that a try thank you very much

 

[rocksolidsr]

i tried hooking up your circuit however with no current going through the sensor the sounder was on continuous and once i applied current it started to beep really fast.

on your drawing, which inputs are the inverting and non-inverting inputs of the op amps

thanks

 

[OperaHouse]

I'm not sure I know how to put this.

You have a nice current probe.
Certainly not a cheap scope.
A cad system.
And you are likely getting paid for this.

I'm sitting in a cabin in the woods with no electric.
The omission of the input polarities was on purpose. You said you were familiar with analog design. This is a good circuit with minimal components. This is Engineering Tips. I've given you a direction and you just need to fine tune the threshold and lengthen the time constant.

 

[MacGyverS2000]

Opera,

See my previous comment...

Dan - Owner

http://www.Hi-TecDesigns.com