Kirk Wallace wrote: > > I guess I need a little more help than I thought. Here is my first pass > at your board schematic: > > http://www.wallacecompany.com/machine_shop/Shizuoka/watchdog-1a.png
That looks correct. > I guessed at the FET array pins and some bits are missing but I think I > got the watchdog part. You guessed right. > If the input is constantly low the signal to the FET will be low. Yep. > If the input is constantly high, the signal to the FET will be the division of > R2 and R5? 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. > 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). 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 ------------------------------------------------------------------------- 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
