How Stage 3 Uses G, F, And E
Stage 3 is not separate from the counter display. In the 00-to-30 version it borrows three segment outputs from the Stage 2 tens display, specifically the g, f, and e pins from the tens CD40110 display output, then decodes those three signals into the LED and reset states.
Why G-F-E Is Used
The units digit changes from 0 to 9 every cycle, so it cannot tell the circuit whether the count is in the green, yellow, high-capacity, or reset condition. The tens digit changes only when the count passes 9, so it carries the range information Stage 3 needs.
In the supplied condition sheet, each seven-segment digit is written in gfedcba order. For the 00-to-30 build, Stage 3 uses the first three bits of that pattern: g, f, and e.
What Stage 3 Receives
When the count is 00 to 09, the tens digit is 0, so the pattern is 0111111. From that, g = 0, f = 1, and e = 1.
When the count is 10 to 19, the tens digit is 1, so the pattern is 0000110. From that, g = 0, f = 0, and e = 0.
When the count is 20 to 29, the tens digit is 2, so the pattern is 1011011. From that, g = 1, f = 0, and e = 1.
When the count reaches the 30 maximum, the tens digit is 3, so the pattern is 1001111. From that, g = 1, f = 0, and e = 0, which is used for the reset condition.
| Count range | Tens digit | Tens pattern gfedcba | g | f | e | Logic state | Output |
|---|---|---|---|---|---|---|---|
| 00-09 | 0 | 0111111 | 0 | 1 | 1 | g f e = 0 1 1 | Green ON |
| 10-19 | 1 | 0000110 | 0 | 0 | 0 | g f e = 0 0 0 | Yellow ON |
| 20-29 | 2 | 1011011 | 1 | 0 | 1 | g f e = 1 0 1 | Flashing red path ON |
| 30 max | 3 | 1001111 | 1 | 0 | 0 | g f e = 1 0 0 | Reset ON |
Boolean Decoder For Green, Yellow, Red, And Reset
After the tens display gives g, f, and e, the inverter and AND gates turn those three bits into one active state for the 00-to-30 design.
Role Of The 74LS04
The inverter creates the missing opposite signals, NOT g, NOT f, and NOT e. Without these inverted signals, the circuit could not separate the 0, 1, 2, and 3 tens-digit conditions needed by the 00-to-30 design.
Role Of The 74LS08
The AND gates combine the direct and inverted signals. Only one equation becomes true for the selected tens state, so only the matching LED or reset path is enabled.
Why The NE555 And Reset Are Separate
The 20-range warning and the 30-maximum reset are not the same event. The red logic path drives the transistor and relay for the flashing warning, while the 30 condition is decoded separately to stop the count at the maximum point.
Counter Side
The Stage 2 tens counter provides the g, f, and e signals. These signals should stay as logic-level decoder inputs, not power-driver outputs.
Relay Driver Side
The red decode output for the 20-range drives a transistor, which energizes the relay coil. A flyback diode protects the transistor and logic gate from the relay coil's reverse voltage spike.
Timer Side
The relay switches the NE555 flashing circuit into the red LED path. This gives a visible warning while keeping the timer electrically separated from the counter output.
Reset Side
The 30-maximum condition is decoded separately from the red flasher path. That reset line returns the system to the starting count instead of leaving the display beyond the project limit.
PDF References
These PDFs are the written references for the Stage 3 LED decode, the G-F-E count-up-to-30 condition, and the full project partition.
Logic And Timing Files
These are the Stage 3 Proteus project files and exported PDFs from the supplied Proteus folder, with the new G-F-E count-up-to-30 condition pack and the new Stage 2 plus Stage 3 bridge projects added to the LED section.
Decoded LED States
Use these state references while checking the logic files, the explanation PDF, and the new count-up-to-30 condition sheet.
Green State
Count 00 to 09. Normal available-parking state with gfe = 011.
Yellow State
Count 10 to 19. Warning state as the parkade approaches capacity with gfe = 000.
Flashing Red State
Count 20 to 29. The relay enables the NE555 timer to drive the high-capacity flashing warning with gfe = 101.
Reset At 30
Count 30 maximum. The reset path turns on at gfe = 100 so the system returns to the allowed range.
Stage 3 Images
These condition sheets and stage images are preserved from the supplied image folders, including the new G-F-E count-up-to-30 reference, the new Stage 2 plus Stage 3 bridge previews, the extra relay and flyback-diode reference drawings, the added logic-family comparison image, and the new 7408 AND-gate pinout reference.