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 |