Hi all

I'm currently working on a fairly simple circuit design project and have an idea which i'm not quite sure how to implement.

backgournd: - I have a amplified signal coming from a oscillating schmitt-trigger going to a small 8ohm speaker. Idea is to create a simple alarm.

I want to start with a soft beep which gradually builds louder and louder as time increases.

Signal is run by a 3v source controled by a switch, and using a 74HC14 low voltage CMOS Schmitt-trigger

If anyone has any ideas as to how i may be able to implement this in a fairly simple way as circuit size and components need to be kept to a minimum.

Thanks in advance for any help or advice.

Cheers

 

You say you have an amplified signal from a 3V source. Does the amplifier have a volume or a gain control? If it does then you can use an integrator to ramp the volume(gain) from a small value up to some saturation voltage. You will also need a way to reset the integrator for the next cycle.

 

Originally posted by Papabravo@May 3 2006, 02:59 AM
You say you have an amplified signal from a 3V source. Does the amplifier have a volume or a gain control? If it does then you can use an integrator to ramp the volume(gain) from a small value up to some saturation voltage. You will also need a way to reset the integrator for the next cycle.

[post=16743]Quoted post[/post]​

Yeah well the amp isn't much. just a simple voltage amplifier using a transistor. since the current running out of the schmitt trigger is only 25mA.

So if you think i can still use an integrator to ramp the gain. then sweet and thanks heeps for your help

 

Originally posted by Kezz@May 2 2006, 11:38 PM
Yeah well the amp isn't much. just a simple voltage amplifier using a transistor. since the current running out of the schmitt trigger is only 25mA.

So if you think i can still use an integrator to ramp the gain. then sweet and thanks heeps for your help

[post=16758]Quoted post[/post]​

Well, I was thinking of an IC Audio Amplifier like an LM386

 

yeah i was think'n of using that as well. just thought a transistor would keep component numbers down. either way. i'm still in the design phase atm and if you think using the LM386 would work better. and make it easyer to implement the integrator than. i'm all ears.

 

Originally posted by Kezz@May 3 2006, 02:02 AM
yeah i was think'n of using that as well. just thought a transistor would keep component numbers down. either way. i'm still in the design phase atm and if you think using the LM386 would work better. and make it easyer to implement the integrator than. i'm all ears.

[post=16761]Quoted post[/post]​

So does the LM386 have a gain control input or is the gain fixed?

 

You could vary the supply voltage to the output transistor, increasing the voltage would increase the loudness. You could use an RC circuit with your desired time constant and buffer the voltage across the C and use it as the supply for the output transistor. You, then, need to discharge the C once the alarm is reset.

 

Hey guys..

just a thought. would it be easyer to have a ramping gain amplifier or something similar. (getting rid of the LM386 and having the signal straight from the schmitt-trigger at 25mA into a amplifier that relativly slowly amplifies the signal over time to the speaker)

ie. have the signal go through an amplifer that slowly amplifies the signal over time. that way your starting at the low signal and the final output is the maximum output signal.

I guess my thought would be is this possible will it work and how would i go about doing it.

Any thoughts or ideas would be great.

Thanks again

 

Hello:

Just another idea. You may want to check out the National OTA LM13700.

Newark sells them for $1.50 or so.

http://cache.national.com/ds/LM/LM13700.pdf

Spoggles