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How to use piezoelectric disc to light up an LED for 3 seconds?

Last post Mon, Nov 4 2013 1:40 AM by Andrew Beckett. 1 replies.
 Started by Fuh Jeng 31 Oct 2013 10:41 AM. Topic has 1 replies and 2542 views
• Thu, Oct 31 2013 10:41 AM

• Fuh Jeng
• Joined on Thu, Oct 31 2013
• Posts 1
• Points 20
How to use piezoelectric disc to light up an LED for 3 seconds?
 Hi, I am trying to build a circuit that will tell me which person hits a  piezoeletric disc first. Imagine that I have two competitors (A and B) running from 10 feet away, and they are trying to hit a piezo disc that is placed on their own  individual table at their finish line as soon as possible. And whoever comes to their table and hits their piezo disc first wins the game. So, for the competition, I  plan to put out two tables and two piezo discs, one for each competitor. Also, I would like to connect the output of the two piezo discs to a "central" circuit, which contains two LEDs (and other components, which is what I am trying to figure out). For simplicity, let’s say that on the  central circuit I put in a red LED to indicate if competitor A hits his piezo disc  first, and another LED (say green) if competitor B hits his disc  first. I want to design a circuit that will light the red LED and make it stays  on for a few seconds (e.g., 3 seconds) if competitor A hits his disc first. And  during the 3 seconds, the green LED will remain dark, even if the competitor B  hits his disc within the 3 seconds time interval. The same logic applies if the  competitor B hits his disc first. In this case, the green LED will light up and  stay on for 3 seconds. And during the 3 seconds, the red LED will not light. My problem #1 is that the electric output of a piezo disc is likely a  transient biphasic pulse. How am I going to use it to light up an LED for 3  seconds? So, my thinking now is to use a simple peak-detector circuit (with a fast attack time-constant and a very slow decay time-constant) to detect and  hold the maximum voltage value for 3 seconds. Apparently, I will need to provide some DC voltage in this circuit to boost the power in order to light up the LED for 3 seconds. But, does this make sense and will this work? My problem #2 is that I don’t know what circuit I shall use to keep the “loser’s” LED dark when the “winner’s” LED stays on for 3 seconds. That is, the winner can be the competitor A or B, depending on who hits his disc first. There is no "tie" condition. I want to do this totally analog, i.e., using only physical electronic parts and no computer nor software on the competition field.  Any suggestion will be greatly appreciated. Sincerely, Fuh Jeng
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• Post Points: 20
• Mon, Nov 4 2013 1:40 AM

Re: How to use piezoelectric disc to light up an LED for 3 seconds?
 This is probably not the best place for such a question.. The Mixed Signal Design forum is mainly for IC mixed-signal design (i.e. design of mixed signal integrated circuits), and even then tends to have more of a tool and methodology focus rather than design.You'd probably be better off using one of the other forums on the internet (maybe on the "Designer's Guide"?). But in the meantime, I'll move this to the PCB Design forum, as it's probably more appropriate.Regards,Andrew.
• Post Points: 5