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I have a basic commerical alsrm system that has a single piezo sounder. There is no other means to output an alarm indication. I need to contrll a relay and have that relay turn on other conventional 12 votl alarm sirens. In the past I have used a simple transistor circut across a regualr speaker input and tha audio source going to the speaker would switch on the relay. I tried connecting this circuit to the piezo speaker. it was able to power on the relay but the volume to he piezo was reduced by 2/3. I know that the a piezo speaker is very different from a regular speaker. Other than that I am at a loss as to how I can accomplish this. Does anyone have a simple circuit that I can construct so that Ican maintain the original volume and still switch on a relay.

Can you show us (draw the schematic with the built-in editor) the transistor circuit you used before? Without more information, I can only guess, but if your original circuit used a BJT you could build a similar circuit with a MOSFET and get the result you want.

I do have an drawn mage of the ckt I used but I do not see any means to post it here with this answer. Too much trouble to re-vceate it with the editor. How can I posty an image? Never sen a forum where I can not paste or otherwise post an image.

Just to the left of the edit box where you type your answer is a button labeled Add Circuit. This button is also available when you are editing your question.

Alternatively, you can find a free image repository, scan your drawing (or sketch), and export it there, then, supply, here, the public url. You probably need to give public access to the image, dependent on your selected image repository.

Sorry for being a little critical on how this form is configured. Just strange how posting/pasting of images, etc, is restricted.

I looked back and found the link to the ckt I referenced in my original post.

Someone mentioned perhaps using a MOSFIT instead of the transistor. I would like to see that concept or any other ideas.

http://www.circuitdiagram.org/audio-activated-relay-switch.html