From: scientist77017@gmail.com   
      
   On Tuesday, May 14, 2019 at 5:53:47 AM UTC-5, default wrote:   
   > On Mon, 13 May 2019 19:22:56 -0700 (PDT), AK   
   >  wrote:   
   >   
   > >Electronic can be quite frustrating.   
   > >   
   > >I put together a circuit for a laser alarm.   
   > >   
   > >It does not work.   
   > >   
   > >There is no way to tell if a design will be successful even if you follow   
   the authors exact directions.   
   > >   
   > >I will keep plugging away and reading Practical Electronics for Inventors.   
   > >   
   > >:-)   
   >   
   > If you look at the schematic and have some idea in your mind on how it   
   > is supposed to work... you take your multi-tester and measure a few   
   > things like the junction of the resistor and LDR.  If it is greater   
   > than .6 volts the transistor (assuming you used a bipolar junction   
   > transistor) should switch on.   
   >   
   > Or are you using the 555 schematic?  (The trigger for a 555 has to be   
   > less than 1/3 the supply voltage)  12V supply the trigger has to dip   
   > lower than 4V...   
   >   
   > Use logic and think about what is supposed to be going on then use the   
   > meter to see what is really going on.   
      
   How specifically do I measure the junction of the resistor and the LDR?   
      
   I am using the 555 chip.   
      
   Andy   
      
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