Logic
module
Schematic
The logic module generates the pump and fluid flow signals, performing logic on signals from the switching module. The PUMP ON, PUMP OFF, and FORWARD FLOW signals are then used in the solid state relay module. Here is a schematic of the different logic components.
Components:
-
555 timer
- 74132 NAND Schmitt trigger
- 74109
J-Q’ flip-flop
- 74221 monostable multivibrator
- 7400 NAND gate
- 74128
NOR gate
Forward
Flow Signal
The
signals controlling forward flow are the panic, forward flow start, and forward
flow stop signals from the switching
module. The logic module sequences
these signals via a 74109 J-K’ positive-edge triggered flip-flop. The CLK
input to the flip-flop is generated by a 555 timer. The CLR input to the flip-flop
is generated by two 74132 Schmitt trigger nand gates so that when the power
is turned on, the 74109 is cleared.
The
following table summarizes the outputs of this module for the panic and forward
flow inputs.
|
Panic |
FF
stop |
FF
start |
FF |
|
1 |
0 |
1 |
0 |
|
0 |
0 |
1 |
1 |
|
0 |
1 |
0 |
0 |
|
0 |
0 |
0 |
No
change |
|
1 |
1 |
0 |
0 |
|
1 |
0 |
0 |
0 |
|
1 |
1 |
1 |
0 |
|
0 |
1 |
1 |
0 |
Pump
Signal
The
pump is turned on and off in the logic module by pump signal and the level
signal from the switching
module. The level signal is high when the pump level is adequate and is
low if the level is inadequate. When the pump switch is turned ON, the two
NAND gate Schmitt triggers generate a rising edge signal and when the pump
is turned OFF, they generate a falling edge. These edge signals enter the
74221 monostable multivibrators, which generate positive or negative pulses.
These pulses control the state of the pump.
The
following table summarizes the outputs of this module for the level and pump
inputs.
|
Pump
switch |
Level
signal |
Pump
on |
Pump
off |
|
0 |
1 |
0 |
1 |
|
0 |
0 |
0 |
1 |
|
1 |
1 |
1 |
0 |
|
1 |
0 |
1 |
0-then
1 after pulse |