On Fri, 2008-04-25 at 23:17 -0400, John Kasunich wrote: > Kirk Wallace wrote: ... snip > > If the input is constantly high, the signal to the FET will be the division > > of > > R2 and R5?
Dooh. It's as plain as day that R2 is grounded. Somehow I visualized current going through R2, the diodes, R5 then ground. Any current in R2 goes to ground only. > > Nope. If the input is constantly high, the signal to the FET will be > low. One end of the diode string is grounded, and the other end is > connected to ground through a resistor that requires a DC current to > develop any voltage across it. Neither C1 nor C2 will pass DC. The > only way to get any voltage on the FET is to have an AC voltage on C1 > and C2 that the diodes can rectify. I see the basics of it now. The math is beyond me but I can breadboard it to get it working. > > > What I need is; 0 to < x Hz = low, x Hz to high = low, x Hz = > > high, or a band-pass filter. > > I'm having trouble parsing that ;-) > > I don't think I've ever seen a charge pump that was a bandpass. They > turn on as long as the input is above some minimum frequency, and off > for DC (either steady high or steady low). Yes, right again. A band pass would do what its name suggests, which is pass the selected frequency through unchanged, instead of converting it to a digital indicator. > In this design, the minimum frequency is determined by the values of C1, > C2, and R5. The size of C1 and C2 determine how much charge is pumped > into C3 on each cycle, and R5 determines how fast that charge bleeds off > and must be replenished. > > C3 is less critical - but it needs to be at least 10x the value of C1 > and C2, to make sure a single edge as might be generated during boot or > driver loading can't charge it up enough to turn things on. If C3 is > too big, it will take a long time (relatively) to turn off when the > input stops toggling. > > Regards, > > John Kasunich I probably don't have any 7414's in hand. For now, I wonder if I can use a couple of NPN's with the load and pull up resistors on the collectors and the emitters tied to ground to make them inverters. I guess I'll find out tomorrow. Thanks for your help. It is fairly dramatic when the main relay unexpectedly kicks in if I forget to throw the disconnect during boot or shutdown. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC/EMC CNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending Craftsman AA 109 restoration Shizuoka ST-N/EMC CNC) ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
