piezo buzzers come in two types,those WITH driver circuits built-in,and bare buzzers,the driver type only need a power supply to make a (VERY) loud noise,the bare ones must provide a square wave (ideally) pulse train at supply voltage,so the supply available makes a big difference,my suggestion is 'suck it and see';try it with what you have,this statement counts for all experimental electronics.Some things work great,some things need 'adjustments',and some things (if you get the maths wrong) go BANG!.at least you dont have to wait for slooow post to try an idea!enjoy experimenting at 120dB but try not to do it at 3in the morning ;^< ----- Original Message ----- From: "Padu" To: "Microcontroller discussion list - Public." Sent: Friday, November 18, 2005 2:33 AM Subject: [EE] Driving piezo buzzers Probably this is a dumb question, but hey, I'm a specialist at dumb questions. In a circuit I'm designing, I want to sound an audible alarm when a certain temp threshold is achieved. I'm going to control this alarm using a PIC. I want to be able to hear that alarm at a certain distance (20-30 meters for example), therefore it must make a good sound. I was looking at some buzzers capable of producing 100dBA at 10cm, but they are rated at 12VDC. Their power consumption is low (8mA) therefore it is feasible to drive it directly from a PIC pin, but at only 5VDC I don't know if it will be loud enough. To speak truly, I don't even know what happens if I plug it to a 5VDC source. I'm guessing it will have a lower volume. I think my main question is this: Do I really need to go the extra mile and chime in an NPN transistor to drive the buzzer? (I do have a 12V power rail on my circuit). Right now I'm thinking about doing it (I mean installing the transistor). I've selected a MMBT123S-7 from diodes inc with a 2.2K between the pic pin and the transistor base. Is it a good selection? Cheers Padu -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist