From: not.here@invalid.invalid   
      
   On Sat, 16 Apr 2011 23:55:20 -0500, flipper wrote:   
      
   > On Sat, 16 Apr 2011 20:19:12 -0700, Big Bad Bob   
   >  wrote:   
   >   
   >>On 04/15/11 03:34, mike s so wittily quipped:   
   >>> On Thursday, April 14, 2011 11:13:26 PM UTC+1, mick wrote:   
   >>>   
   >>>   
   >>>>   
   >>>> I just grabbed that book. Good isn't it?   
   >>>>   
   >>>> Let's see...   
   >>>> opto-isolator fed from bias supply: input into PIC No further action   
   >>>> without bias   
   >>>> PIC ramps up heater(s)   
   >>>> Allow some warm-up time   
   >>>> Close a relay to allow B+ via a resistor Another delay   
   >>>> Close second relay to short out B+ resistor&  allow full supply   
   >>>>   
   >>>> owzat?   
   >>>>   
   >>>>   
   >>> Nice,  a "finite state machine".   So now all that's needed is   
   >>> something similar for safe power down,  oh and the nasty cases for   
   >>> when the person switching it on, or off, changes their mind part way   
   >>> through a sequence and throws the switch the other way.   
   >>   
   >>properly handling rapid on/off sequences would be a 'nice touch'.  I'd   
   >>start the sequence from the beginning again each time.  Probably the   
   >>safest way.  As for power off, easiest method, just "power off".   
   >>   
   >>> My PSU is very simple, but as it has a fairly hefty directly heated   
   >>> rectifier I added a thermistor to protect against power switch jitter   
   >>> - which would tend to blow the mains fuse.  Almost certainly because   
   >>> the rectifier was warm, but the smoothing cap discharged, so the   
   >>> rectifier behaved more like silicon than vacuum on these occasions.   
   >>   
   >>thermistors and similar components seem to be the most common way of   
   >>handling this 'old school' style.   
   >   
   > Using a PIC strikes me as 'overkill' style.   
      
      
   Me too - but I just happen to like 'em! :-)   
   I've always liked nice simple RC timers, but a PIC is so cheap and easy   
   to use that they can easily work out cheaper. Also, you can change your   
   mind as to exactly how you want them to work without major rebuilding. As   
   for reliability, I suspect that they are pretty good. The PSU components   
   are more stressed.   
      
   I definitely like thermistors in transformer primaries. So simple, but so   
   effective.   
      
   --   
   Mick                      (Working in a M$-free zone!)   
   Web: http://www.nascom.info   
   Filtering everything posted from googlegroups to kill spam.   
      
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