clock selecting using 556 and NAND problem
Again I have found myself stuck on an EE problem, and I need some help. I
have implemented a stepper motor drive that requires a dir and step. This
works but the pulsing was consuming too many stamp clock cycles. I then
hooked up a 556 timer to the input and added another control pin for speed.
Now I have 3 pins for direction/on-off/speed control. However the 7400 CMOS
Quad 2-input NAND gates aren't detecting the individual pulses. They are
always detecting an on-state. My guess is that the 556 aren't generating a
full 5 or 0 volts. How do I fix this? pull-down or up resistors? I am
stuck. Any help would be great.
Diagram (each square is a nand gate)
____ ____
CLK 1
|nand|0---\ ENABLE-|nand|
Speed CTRL---|____| \_________ |____|0
to board
|_|nand| ____ /
|_|____|0--|nand|0-/
CLK 2
|____|
-Sean
[noparse][[/noparse]Non-text portions of this message have been removed]
have implemented a stepper motor drive that requires a dir and step. This
works but the pulsing was consuming too many stamp clock cycles. I then
hooked up a 556 timer to the input and added another control pin for speed.
Now I have 3 pins for direction/on-off/speed control. However the 7400 CMOS
Quad 2-input NAND gates aren't detecting the individual pulses. They are
always detecting an on-state. My guess is that the 556 aren't generating a
full 5 or 0 volts. How do I fix this? pull-down or up resistors? I am
stuck. Any help would be great.
Diagram (each square is a nand gate)
____ ____
CLK 1
|nand|0---\ ENABLE-|nand|
Speed CTRL---|____| \_________ |____|0
to board
|_|nand| ____ /
|_|____|0--|nand|0-/
CLK 2
|____|
-Sean
[noparse][[/noparse]Non-text portions of this message have been removed]
Comments
properly....they will drive TTL or CMOS gates directly. Don't forget that a
NAND gate outputs a 0 when both inputs are 1. Is this what you want...you
have to make sure that you want that function. Remember that a positive logic
NAND gate ia a negative logic OR gate. (DeMorgans theorem). You can use a
pull-up resistor if you want but I don't think that is your problem!
[noparse][[/noparse]Non-text portions of this message have been removed]