creating a switched circuit for turn signals using the parking light

[broly]

i found this:

https://www.eevblog.com/forum/projects/turn-signal-blinker-using-mosfet/


but in my opinion this seems complex. also i readily admit i'm stupid and have never used MOSFETs or anything before.

however i found this useful SO post: https://electronics.stackexchange.com/questions/462897/parking-light-and-signal-light-with-same-led-using-mosfets

one commentor suggested using a XOR gate, which i believe is a great idea.

problem is (to which the initiated will say "of course") is the low current, meaning it can only be used to output the signal but not the current.

in this case, is it a matter of using a MOSFET so that the output signal from the XOR is reliably detected and then switching the real voltage?

as always i greatly value the concentrated intellect of this audience, and i apologise if my question is deemed an irresponsible expenditure of it

[thm_w]

Can you be very specific as to what exactly you want to do:
- Have the turn signals come on when parking light is on?
- Turn signals off when parking light is on?

[broly]

Can you be very specific as to what exactly you want to do:
- Have the turn signals come on when parking light is on?
- Turn signals off when parking light is on?

good question, and upon further reflection i realised that i confused everyone by assuming the stackoverflow recommendation would work.

what i want is:
- LIGHT ON when turn signal wire sends ON, and parking light is ON
- LIGHT OFF when turn signal wire sends OFF, and parking light is ON
- LIGHT ON when the turn signal wire sends ON, and parking light is OFF
- LIGHT OFF when the turn signal wire sends OFF, and parking light is OFF.

let P be parking light
let S be the turning stalk
introducer auxiliary variable T (actual on/off of turn signal itself) to demonstrate behaviour at the light

we have input for P and S but not T, which is why it's considered auxiliary

P T S | OUTPUT
1 1 1 | 1
1 0 1 | 0
1 1 1 | 1
0 1 1 | 1

1 0 0 | 1
0 0 1 | 0
0 1 0 | N/A (not possible)
0 0 0 | 0

so pretty much i want the 'off' of the turn signal to be respected and interrupt the parking light signal (if/when it's on).

using relays won't work as it would give an "out of sync" blinker if the turn signal circuit was used to energise a 5 pin relay

i thought an XOR would work because i didn't think hard about it lol, but clearly the P \or T = 0 of the XOR would be a problem :/

thanks to your question thom, i realised i need a third variable. the turning stalk signal itself is more important

[thm_w]

From what I can understand, all you want to do is mirror the turn signal output to an extra light. So now the question is: one light for each turn signal? or both turn signals control one light?

If you are ORing both turn signals, you can have a diode coming from each turn signal wire and feeding another light.
Since you don't want to overload the turn signal drive circuitry, you can have that signal feed into a low side mosfet or a relay which drives your light.

[broly]

Quote from: thm_w on Yesterday at 11:33:53 pm

From what I can understand, all you want to do is mirror the turn signal output to an extra light. So now the question is: one light for each turn signal? or both turn signals control one light?

If you are ORing both turn signals, you can have a diode coming from each turn signal wire and feeding another light.
Since you don't want to overload the turn signal drive circuitry, you can have that signal feed into a low side mosfet or a relay which drives your light.

]

it's not mirroring the turn signal because the signal at the light i want to do this, is configured as the parking light. but i can/will run the turn signal wire to this light.

so it's more about adding turn signal behaviour to the parking light, without adding a light. this is why i was fascinated by these gate ICs

edit: move to new post after what thom wrote

[thm_w]

OK understood.

So you'd end up cutting the signal to the parking light, and feeding it instead with your logic generated signal, which has either a FET or relay on the output as a higher strength drive.

I think you can feed the truth table into a logic gate calculator and see what it will suggest, or figure it out by hand.

[broly]

after abusing the AI with a metre stick a few times, this is what we have;

------------------------------
## Forum Draft Teaser (For your EEVblog Thread)
If you want your friends to appreciate the theatricality, you can intro your schematic text with a caption like this:

Gentlemen, behold... my latest creation. I call it... "The Light Activator."

No, it doesn't involve sharks with frickin' laser beams attached to their heads, but it
does combine raw 12V automotive power with the absolute perfection of 4000-series CMOS
logic.

I demand the community scrutinize this blueprint before I deploy it to the four corners
of my vehicle for a total cost of... ONE MILLION DOLLARS! (Or, you know, about
forty bucks on DigiKey).

Here is a clean, well-spaced plain-text breakdown of your complete project. It is perfectly formatted to copy-paste straight into an EEVblog forum post, allowing the community to review the hardware architecture, logic math, and component selection.

1. LOGICAL EXPRESSION & TRUTH TABLE
This circuit solves the conditional transmission gate problem where S (Control) physically gates the wire routing T (Signal), while integrating P (Primary) as an independent override line.Mathematical Expression:OUTPUT = NOT( NOT(P AND NOT(S)) AND NOT(T AND S) )Functional Equivalence (via De Morgan's Law):OUTPUT = (P AND NOT S) OR (T AND S)The 3-Input Integrated Truth Table:

Code: [Select]

P │ T │ S │ Transmission Line State │ OUTPUT
───┼───┼───┼─────────────────────────┼────────
 0 │ 0 │ 0 │ T is blocked (0)        │   0
 0 │ 0 │ 1 │ T passes through (0)    │   0
 0 │ 1 │ 0 │ T is blocked (0)        │   0
 0 │ 1 │ 1 │ T passes through (1)    │   1
 1 │ 0 │ 0 │ T is blocked (0)        │   1
 1 │ 0 │ 1 │ T passes through (0)    │   0
 1 │ 1 │ 0 │ T is blocked (0)        │   1
 1 │ 1 │ 1 │ T passes through (1)    │   1


2. ASCII LOGIC DIAGRAM (NAND-ONLY IMPLEMENTATION)To ensure high-reliability native 12V operation under automotive conditions, the layout is broken down into four standard 2-input NAND gates using a single CD4011BE CMOS chip.

       

Code: [Select]


========================================================================================================
                      UPDATED STANDALONE NODE ARCHITECTURE WITH PULSE FILTER
========================================================================================================

 P ────[1kΩ]───┬───────────────────────────────────────────────┐
               │                                               │
            [Zener]                                            │
               │                                               ▼
            [10kΩ]                                          ╔═════════════╗
               │                                            ║   NAND 2    ║───┐
              GND                     ┌────────────────────>║  (Gate 2)   ║   │
                                      │                     ╚═════════════╝   │
 T ────[1kΩ]───┬──────────────────────┴───────┐                               │
               │                              ▼                               │
            [Zener]                        ╔═════════════╗                    ▼
               │                           ║   NAND 3    ║──┐              ╔═════════════╗
            [10kΩ]                         ║  (Gate 3)   ║  │              ║   NAND 4    ║─── OUTPUT
               │                           ╚═════════════╝  │              ║(Final Mixer)║    (Pin 11)
              GND                                 ▲         │              ║  (Gate 4)   ║
                                                  │         └─────────────>║             ║
                                                  │                        ╚═════════════╝
                                                  │                               ▲
                                            [Internal S]                          │
                                                  │                               │
                                            ┌─────┴───────────────────────────────┘
                                            │
                                      [1N4148 Diode]
                                            │
                                            ▼
                                       ┌──────────┐
                                       │ 10µF Cap │
                                       └──────────┘
                                            │
                                           GND



3. AUTOMOTIVE HIGH-CURRENT OUTPUT BLOCKThe output pin of NAND 4 safely drives an N-Channel Power MOSFET to control the high-current light loop without mechanical wear points.

Code: [Select]


=============================================================================================================================================
                                      AUTOMOTIVE HIGH-CURRENT LOGIC & SWITCHING SIGNAL FLOW DIAGRAM
=============================================================================================================================================

 [RAW VEHICLE SIGNAL INPUTS]               [INPUT CONDITIONING STAGE]                    [CORE CMOS NAND LOGIC MATRIX]
 ───────────────────────────               ──────────────────────────                    ─────────────────────────────

 (From Switch P) ───┬────────────────────► [1kΩ Resistor] ───┬───► [Conditioned P] ────► Pin 6 (NAND 2 Input B) ──┐
                    │                                        │                                                   │
                    ▼                                        │                                                   ▼
             (Powers Light)                               [Zener]                                         ╔═════════════╗
                    │                                        │                                            ║   NAND 2    ║───┐
                    │                                     [10kΩ]                                          ║ (Gate 2)    ║   │
                    ▼                                        │                                            ╚═════════════╝   │
         ╔═════════════════════╗                            GND                                                  │          │
         ║ LIGHT FIXTURE       ║                                                                                 ▼          │
         ║ (Gets Power from P) ║                                                                          Pin 12 (NAND 4)   │
         ╚═════════════════════╝                                                                                    │          │
                    │                                                                                               │          │
                    ▼                                                                                               │          │
         [LIGHT NEGATIVE RETURN]                                                                                    │          │
                    │                                                                                               │          │
                    │ (Enters Plug Pin 5)                                                                           │          │
                    ▼                                                                                               │          │
                 [M_Dr] (Hole C28)                                                                                  │          │
                    │                                                                                               │          │
                    ├──────────────────────► [1kΩ Resistor] ───┬───► [Conditioned T] ────► Pin 9 (NAND 3 Input A) ───┤          │
                    │                                          │                                                    │          │
                    │                                       [Zener]                                                 ▼          ▼
                    │                                          │                                           ╔═════════════╗╔═════════════╗
                    │                                       [10kΩ]                                         ║   NAND 3    ║║   NAND 4    ║──► FINAL OUT
                    │                                          │                                           ║ (Gate 3)    ║║ (Final Mixer)  (Pin 11)
                    │                                         GND                                          ╚═════════════╝╚═════════════╝
                    │                                                                                               ▲            ▲
 (Pulsing Turn Stalk)                                                                                               │            │
 [ HARNESS WIRE T ] ───────────────────────────────────────────┴───► [1N4148 Diode] ──┐                            │            │
                                                                                      ▼                             │            │
                                                                                 [10µF Cap] ──┬── Pin 10 (NAND 3) ──────┘            │
                                                                                      │       │                                  │
                                                                                     GND      └── Pin 1 (NAND 1) ────────────────────┘
                                                                                              (Internal Detected S Line)
 ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
 [HIGH-CURRENT LOW-SIDE SOLID-STATE OUTPUT SWITCHING STAGE]                                                                 
 ──────────────────────────────────────────────────────────                                                                 
                                                                                                                             
   [ FINAL LOGIC OUTPUT ] ──► [ Hole A11 ] ──► [ 1kΩ Resistor [R4] ] ──► [ Hole A28 ] ──► ╔═══════════╗                             
 (From CD4011BE Pin 11)                                                                   ║   GATE    ║ (Hole B28)                   
                                                                                          ║           ║                             
                                                                                          ║  IRFZ44N  ║                             
                                                    [VISHAY 1N4007]                       ║  MOSFET   ║                             
                                                  ┌───[FLYBACK DIO]──────────────────────>║           ║                             
                                                  │                                       ╚═══════════╝                             
   [ CONTINUOUS +12V RAIL ] ──(Cathode Stripe)────┘                                             │                                     
   (Powers CD4011BE Pin 14)                                                                     ▼                                     
                                                                                            [M_Sr] (Hole A29)                         
                                                                                                │
                                                                                                ▼ (Enters Plug Pin 2)                 
                                                                                      [ MASTER CHASSIS GROUND ]                       
=============================================================================================================================================


4. DIGI-KEY SHOPPING CART (SCALED FOR 4 MODULES)To ensure this survives vehicular vibrations, the build drops plastic solderless breadboards entirely. It switches to a distributed multi-box architecture consisting of four independent, shielded modules located at each corner of the car.The list leverages TE Connectivity for premium passive components alongside AEC-Q101 equivalent silicon leaders (Texas Instruments, Infineon, onsemi, and Vishay).

• Hammond Mfg 1551SNAPBK Snap-Together Box
  • Quantity: 4
  • Part Number: 1551SNAP3BK
  • Link: digikey.ca
  • Purpose: Toolless ABS enclosures protecting each independent corner circuit module from road debris.
• Adafruit 1608 Perma-Proto Breadboard PCB
  • Quantity: 4
  • Part Number: 1608
  • Link: digikey.ca
  • Purpose: Gold-plated, through-hole proto-boards that fit inside the enclosure and won't drop components under vibration.
• Texas Instruments CD4011BE Quad NAND IC
  • Quantity: 4
  • Part Number: CD4011BE
  • Link: digikey.ca
  • Purpose: CMOS core logic chip operating natively at 12V to handle vehicle battery charging voltage profiles.
• Assmann WSW 14-Pin IC Protective DIP Socket
  • Quantity: 4
  • Part Number: A 14-LC-TR
  • Link: digikey.ca
  • Purpose: Isolates the CD4011BE silicon pins from high thermal stresses during hand soldering.
• TE Connectivity CFR25J1K0 1 kΩ Carbon-Film Resistors
  • Quantity: 12 (3 per corner board)
  • Part Number: CFR25J1K0
  • Link: digikey.ca
  • Purpose: Premium TE inline current-limiting buffer resistors filtering raw line transients on inputs P, T, and S.
• TE Connectivity ROX1SJ10K 10 kΩ Flameproof Resistors
  • Quantity: 12 (3 per corner board)
  • Part Number: ROX1SJ10K
  • Link: digikey.ca
  • Purpose: Heavy-duty 1-Watt pull-down resistors to enforce clean low states when inputs drop out.
• onsemi 1N4742A 12V 1W Zener Clamping Diodes
  • Quantity: 12 (3 per corner board)
  • Part Number: 1N4742A
  • Link: digikey.ca
  • Purpose: Clips high-voltage surges over 12V safely down to ground right at the input boundary.
• Infineon IRFZ44NPBF Power MOSFET
  • Quantity: 4 (1 per corner board)
  • Part Number: IRFZ44NPBF
  • Link: digikey.ca
  • Purpose: Solid-state N-Channel switch to drive the heavy lamp load quietly without mechanical relays.
• Vishay 1N4007 High-Voltage Flyback Diodes
  • Quantity: 4 (1 per corner board)
  • Part Number: 1N4007-E3/54
  • Link: digikey.ca
  • Purpose: Suppresses inductive kickbacks from long vehicle wire bundles when switching off the lamps.

To lean into the Austin Powers theme for your EEVblog post, you can pitch the project with a heavy dose of dramatic flair. Presenting a relatively straightforward 12V lighting controller as a "highly classified, over-engineered vehicular command module" is exactly the kind of humor that resonates well with engineering forums.
Here is the exact pin-to-pin track layout for the CD4011BE, written out as a blueprint ready to show your peers.
------------------------------
THE DR. EVIL "MASTER PLAN" PINOUT MAP (CD4011BE)A standard CD4011BE contains four independent 2-input NAND gates inside a single 14-pin package. To execute the logic seamlessly, wire the pins on your Adafruit Perma-Proto board using this blueprint:

• Power & Ground Rails
  • Pin 14 (VDD): Connect directly to your clean, conditioned +12V Power Bus.
  • Pin 7 (VSS/GND): Connect directly to your Chassis Ground Bus.
• Gate 1: The "S Inverter" (~S)
  • Pin 1 (Input 1A): Connect to conditioned Input S.
  • Pin 2 (Input 1B): Connect directly to Pin 1 (tying inputs together creates a NOT gate).
  • Pin 3 (Output 1): Outputs NOT S. Run a jumper wire from here to Pin 5.
• Gate 2: The "Primary Override Selector" [P AND ~S]
  • Pin 5 (Input 2A): Connect to Pin 3 (receiving the NOT S signal).
  • Pin 6 (Input 2B): Connect to conditioned Input P.
  • Pin 4 (Output 2): Outputs NAND(P, NOT S). Run a jumper wire from here to Pin 12.
• Gate 3: The "Transmission Pass-Through" [T AND S]
  • Pin 8 (Output 3): Outputs NAND(T, S). Run a jumper wire from here to Pin 13.
  • Pin 9 (Input 3A): Connect to conditioned Input T.
  • Pin 10 (Input 3B): Connect to conditioned Input S.
• Gate 4: The "Final Mixer" (The Output Stage)
  • Pin 12 (Input 4A): Connect to Pin 4 (Output 2).
  • Pin 13 (Input 4B): Connect to Pin 8 (Output 3).
  • Pin 11 (Output 4): This is your FINAL LOGIC OUTPUT. Connect this directly to the Gate of your IRFZ44N MOSFET through a 1kΩ resistor.

If you want to take the forum review further, I can help you draft the troubleshooting guide for your friends to check, or look up AEC-Q101 automotive enclosure alternatives if you want to ensure the boxes are fully dustproof. Which would you prefer?


---- i have to check all of this, but i wanted to share what i got

[Zero999]

I don't have time to completely read the entire thread, so apologies in advance if I've missed anything. I have looked at your schematic though.

It appears as though you've misunderstood how the circuits in the other thread work. They use a technique known as bootstrapping, which enables an N-channel MOSFET to switch the positive side of a load.

Look at the CMOS oscillator circuit. Three gates are used for the oscillator rather than two, because it's more likely to oscillate and there are four in the package, so it makes sense to use them. The final gate before the MOSFET is just a buffer.
Refer to the Fairchild application note for more information.
https://opencourses.uoc.gr/pluginfile.php/11496/mod_resource/content/1/extra03_osc.pdf

Now for the important part, regarding bootstrapping. When Q1 is off, C1 charges through D1 and the load, which is an LED lamp in this case, hence the parallel resistor suggestion made in the thread. C1 slowly charges up to the supply voltage, minus a diode drop. When Q1 turns on, D1 prevents C1 from discharging through the MOSFET, so the source voltage rises up towards the supply, with the gate voltage sitting at near the supply voltage. I provided a SPICE simulation of this but for a different circuit in the original thread.



The circuit you posted lacks the bootstrap capacitor and diode, so cannot work. The MOSFET will simply act as a source follower, dropping a few volts.

[Someone]

I don't have time to completely read the entire thread, so apologies in advance if I've missed anything. I have looked at your schematic though.

The bits you didn't read are an extended output of AI working from misguided prompts. So all the content is only diverging further away from any real solution.

Car lamps, logic equation, no access to a/the ECU code.... that'd be a relay

Logic gates are entirely the wrong tool for what the OP is (probably) asking. Inconsistent (and edited later) truth tables and explanations not helping.

[broly]

I don't have time to completely read the entire thread, so apologies in advance if I've missed anything. I have looked at your schematic though.

The bits you didn't read are an extended output of AI working from misguided prompts. So all the content is only diverging further away from any real solution.

Car lamps, logic equation, no access to a/the ECU code.... that'd be a relay

Logic gates are entirely the wrong tool for what the OP is (probably) asking. Inconsistent (and edited later) truth tables and explanations not helping.

a relay won't work. it's been tried before. the problem with a relay is that it will not sync the turn signal with the parking light.

what exactly is wrong with the AI circuit? i should note that i updated the diagrams because it needed to be told T is not an input. it understands that T (whether the light is ON or OFF) is gated by S (the turn signal switch stalk).

it is a low-side ground from what i can see. the chip is used to replicate the truth table, and the inputs are the turn stalk and turn signal switch (which itself gates the turn signal value).

it seems the circuit acts as a low-side switch? and since the output of the gate is very weak, you use the mosfet to pull the signal down.

i am still checking the diagrams because both 'S' and 'T" are on the same wire, which makes it tricky. but the idea of an inverter seems necessary and this is why a relay can't work?

i don't know how you'd get a relay solution to work.

i am far from one to use these chatbots for something like this, but having laboriously explored the relay approach (that does NOT have the ability to give you a SYNCED turn signal), i am eager to hear your wisdom on how i'm wrong

chances are i won't hear it.

[PCB.Wiz]

It appears as though you've misunderstood how the circuits in the other thread work. They use a technique known as bootstrapping, which enables an N-channel MOSFET to switch the positive side of a load.
Look at the CMOS oscillator circuit. Three gates are used for the oscillator rather than two, because it's more likely to oscillate and there are four in the package, so it makes sense to use them.

A better choice for low speed oscillator would be 4093 or 40106, those have hysteresis and lower peak currents.

[PCB.Wiz]

what i want is:
- LIGHT ON when turn signal wire sends ON, and parking light is ON
- LIGHT OFF when turn signal wire sends OFF, and parking light is ON
- LIGHT ON when the turn signal wire sends ON, and parking light is OFF
- LIGHT OFF when the turn signal wire sends OFF, and parking light is OFF.
...
using relays won't work as it would give an "out of sync" blinker if the turn signal circuit was used to energise a 5 pin relay

Parking lights are red at the rear, right ?
I'm not sure flashing a red light with turn is actually legal. (or safe)

If you want in phase action, that needs more than simple gates.

The easiest is a simple retriggerable monostable timer of slightly over the turn period.
When the turn flashes, the retrigger keeps the output connected to turn, and when it ceases, the timeout reconnects back to the park, which is either ON or OFF.

You can make a crude monostable with a relay and cap/diode/resistor, using the large skew in CLOSE and RELEASE voltages.

[Someone]

I don't have time to completely read the entire thread, so apologies in advance if I've missed anything. I have looked at your schematic though.

The bits you didn't read are an extended output of AI working from misguided prompts. So all the content is only diverging further away from any real solution.

Car lamps, logic equation, no access to a/the ECU code.... that'd be a relay

Logic gates are entirely the wrong tool for what the OP is (probably) asking. Inconsistent (and edited later) truth tables and explanations not helping.

a relay won't work. it's been tried before. the problem with a relay is that it will not sync the turn signal with the parking light.

Tried by people who are incompetent? Sitting right on my screen is a solution using only relays, that can be wired into the existing loom at either end without adding any additional wires to/from.

The electrical protection of automotive signals in/out of logic might be cheaper in volume production where you're trying to shave cents, but for low volume and one-off where power and cost of goods aren't the dominant drivers then relays are the accepted solution.

i am eager to hear your wisdom on how i'm wrong

chances are i won't hear it.

Have fun with your AI fantasitc Rube Goldberg creations because you reject help.

[Someone]

Parking lights are red at the rear, right ?
I'm not sure flashing a red light with turn is actually legal. (or safe)

Note the OP is flying the null flag. Less than half of the world is under harmonised vehicle standards.

[broly]

what i want is:
- LIGHT ON when turn signal wire sends ON, and parking light is ON
- LIGHT OFF when turn signal wire sends OFF, and parking light is ON
- LIGHT ON when the turn signal wire sends ON, and parking light is OFF
- LIGHT OFF when the turn signal wire sends OFF, and parking light is OFF.
...
using relays won't work as it would give an "out of sync" blinker if the turn signal circuit was used to energise a 5 pin relay

Parking lights are red at the rear, right ?
I'm not sure flashing a red light with turn is actually legal. (or safe)

If you want in phase action, that needs more than simple gates.

The easiest is a simple retriggerable monostable timer of slightly over the turn period.
When the turn flashes, the retrigger keeps the output connected to turn, and when it ceases, the timeout reconnects back to the park, which is either ON or OFF.

You can make a crude monostable with a relay and cap/diode/resistor, using the large skew in CLOSE and RELEASE voltages.

it would be illegal if it was the only turn signal on the rear of the car. in this case the light is an auxiliary one from a "wing spoiler" that has parking lights on the "ears"
https://auctions.yahoo.co.jp/jp/auction/c1130924902

i am still checking the AI's output, but i think what it's saying is the same as what you're suggesting. it's now relying on the output from the turn signal wire itself to determine whether the turning stalk has been activated.

and then it uses 1N4148 check valve to 'block the bleed' based on assumed frequency of a turn signal switch, which sort of makes sense? in its words

Code: [Select]

Here is the text formatted in clean, plain Markdown, ready to copy and paste directly into your EEVblog forum thread.
------------------------------
## Solving the Asynchronous Automotive State Paradox: Breaking the Turn Signal Dark-Phase Loop
When trying to implement the asynchronous logic formula (P && !S) || (T && S) natively in hardware using a standard CMOS CD4011BE Quad NAND chip, a critical physical pitfall occurs during real-world turn signal stalk operations.
Because a turn signal combination stalk (S) acts as an upstream physical router that directs voltage down the line to create the pulsing transmission payload (T), there is no separate "S" wire entering the module box. The module must deduce whether the stalk is clicked on based entirely on the behavior of the T wire.
## The Pitfall
When the stalk is engaged, the turn signal wire alternates. During the hot phase of the flash cycle, T = 1, allowing the circuit to easily deduce S = 1. But when the flasher unit swings into its dark window, the voltage on the wire drops to zero. At that exact split second, T = 0, yet the physical stalk is still clicked down (S = 1).
If the logic chip evaluates the equation instantly during that dark gap, it sees T = 0 and assumes S = 0. This forces the module to slip backwards into the Override Switch Active state loop, which would accidentally fire the output MOSFET and force the auxiliary lights to turn permanently ON during what is supposed to be the flasher’s resting dark phase.
## The Hardware Fix: The RC Integrator Smoothing Flywheel
To bypass this logical loop without introducing software or an aggressive microcontroller, a physical "memory" subsystem is built directly onto the input conditioning stage of the prototyping grid using an RC Integrator network (an on-board diode-capacitor smoothing tank filter):

   1. The 1N4148 Check Valve: The moment the turn signal stalk hits its first hot pulse (T = 1), voltage rushes through an 1N4148 signal diode and charges a 10µF Panasonic electrolytic capacitor instantly. This drives the internal S logic line to a clean, hard 1. When the flasher unit drops into its dark window (T = 0), the vehicle's turn signal wire becomes a cold ground path. The 1N4148 diode acts as a one-way check valve, physically blocking the current from escaping backwards down the harness and forcing the storage capacitor to hold its charge inside the box.
   2. Time-Constant Tuning (τ Math): Because the charge cannot escape backwards through the diode, its only exit path is leaking slowly to ground through a TE Connectivity 10 kΩ pull-down resistor. This creates an electronic RC decay delay curve:
   $$\tau = R \times C$$
   $$10,000\,\Omega \times 0.00001\,\text{F} = 0.1\,\text{seconds}$$
   An electrolytic capacitor takes roughly 5 time constants (5 × τ) to fully drain its voltage beneath the CMOS digital low threshold, giving the internal S line a physical hold-over memory of exactly 0.5 seconds (500 milliseconds).
   3. Bridging the Dark Window: A standard automotive turn signal blinks at a frequency of roughly 1.5 Hz to 2.0 Hz. This means the complete "Dark Phase" where the wire drops to 0V only lasts between 250 to 330 milliseconds. Because the on-board capacitor tank takes 500 milliseconds to drain below the logic threshold, the next hot pulse from the blinker arrives and recharges the tank long before the internal S line ever decays to 0.

## State Execution Matrix

| Flasher Wire State | Real-World Vehicle State | Internal T State | Internal Capacitor Charge Status | Internal Deduced S State | Output Result |
|---|---|---|---|---|---|
| Blinker Hot Flash | Stalk On, Light Striking | 1 | Fully Charged (12V) | 1 | ON (NAND 3 Fires) |
| Blinker Dark Gap | Stalk On, Light Resting | 0 | Slow Decay (Stays above 8.5V) | 1 | OFF (NAND 3 Sleeps) |
| Stalk Clicked Off | Stalk Returned to Neutral | 0 | Complete Drain (Drops to 0V after 500ms) | 0 | OFF (System Reset) |

## Conclusion
By isolating the transient pulsing variable through an analog time-delay filter, Internal S stays locked high at 1 during the flasher's dark gap. Because S remains stable, the primary override branch (P && !S) stays completely locked down and inactive, preventing any phantom light flickering or high-frequency oscillations on the output IRFZ44N MOSFET gate channel.
------------------------------
Now that your forum-ready explanation is prepped, let me know if you are ready to generate the multimeter point-by-point bench validation checklist so you can safely trace these voltage parameters on your physical board!



[broly]

I don't have time to completely read the entire thread, so apologies in advance if I've missed anything. I have looked at your schematic though.

The bits you didn't read are an extended output of AI working from misguided prompts. So all the content is only diverging further away from any real solution.

Car lamps, logic equation, no access to a/the ECU code.... that'd be a relay

Logic gates are entirely the wrong tool for what the OP is (probably) asking. Inconsistent (and edited later) truth tables and explanations not helping.

a relay won't work. it's been tried before. the problem with a relay is that it will not sync the turn signal with the parking light.

Tried by people who are incompetent? Sitting right on my screen is a solution using only relays, that can be wired into the existing loom at either end without adding any additional wires to/from.

The electrical protection of automotive signals in/out of logic might be cheaper in volume production where you're trying to shave cents, but for low volume and one-off where power and cost of goods aren't the dominant drivers then relays are the accepted solution.

i am eager to hear your wisdom on how i'm wrong

chances are i won't hear it.

Have fun with your AI fantasitc Rube Goldberg creations because you reject help.

"i know the answer but i won't share it and i'll assume you're trying to save money with your solution"

did you see my cart? it costs multiples more than any relay solution.

put up or shut up. i admit when i'm wrong and i would happy to see your relay solution that is IN SYNC, but it doesn't exist. you can't use a DPDT or two SPDTs to do this.

[broly]

6000 posts, picked a fight, about to lose. wow. just say "i'm not sharing it" and try to save face here.

thankfully, unlike you, i have no such fear because i am wired to think i'm wrong. it has served me well.

edit: i should call in dave so he can do the forum-equivalent of grabbing this fight-picker's hands to then slap themselves in the face a few times.

reckless disregard with your assumptions. didn't look at the cart to see it costs hundreds of dollars (FOUR of these circuits). as if i wanted to spend MORE when you think i'm trying to spend LESS.

outrageous

[PCB.Wiz]

The easiest is a simple retriggerable monostable timer of slightly over the turn period.

i am still checking the AI's output, but i think what it's saying is the same as what you're suggesting. it's now relying on the output from the turn signal wire itself to determine whether the turning stalk has been activated.

Yes, rather mangled and verbose, but they do mention Tau and timing, so they are creating a R/C/D monostable.
A 50mA relay coil might need somewhere in the ballpark of 2200uF, 
or a MOSFET gate can work with ballpark values of 820k and 470nF to give 638ms with ~2V Vth test MOSFET.

[amyk]

Everyone calm down...

what i want is:
- LIGHT ON when turn signal wire sends ON, and parking light is ON
- LIGHT OFF when turn signal wire sends OFF, and parking light is ON
- LIGHT ON when the turn signal wire sends ON, and parking light is OFF
- LIGHT OFF when the turn signal wire sends OFF, and parking light is OFF.

Just connect the light to the turn signal?

Parking lights are red at the rear, right ?
I'm not sure flashing a red light with turn is actually legal. (or safe)

Red rear turn signals are standard in all of North America.

[PCB.Wiz]

Parking lights are red at the rear, right ?
I'm not sure flashing a red light with turn is actually legal. (or safe)

Red rear turn signals are standard in all of North America.

Interesting.  This is what a quick google search finds :

EU Mandatory Color: Under United Nations Economic Commission for Europe (UNECE) regulations—which are adopted across the EU—rear direction indicators must be amber.

Australia, car turn signals (indicators) must emit an amber, orange, or yellow light and cannot be other colors on modern vehicles.

In Japan, car turn signals must be orange or amber and cannot be red or any other color

In China, car turn signals must be amber, yellow, or orange, and cannot be other colors like red or blue

India: Central Motor Vehicles Rules (CMVR): According to Rule 104 (and related vehicle lighting standards under CMVR, 1989), all motor vehicles in India must be equipped with direction indicators (turn signals) that emit an amber/orange

[Analog Kid]

Everyone calm down...

what i want is:
- LIGHT ON when turn signal wire sends ON, and parking light is ON
- LIGHT OFF when turn signal wire sends OFF, and parking light is ON
- LIGHT ON when the turn signal wire sends ON, and parking light is OFF
- LIGHT OFF when the turn signal wire sends OFF, and parking light is OFF.

Just connect the light to the turn signal?

You can get rid of that question mark; this was exactly my take on this

Why can't you (O.P.) see that you don't need anything except a direct connection between the "LIGHT" and the turn signal? Your description above shows this very clearly.

Everything starting with "and" above is irrelevant and has no effect on the outcome.

[PCB.Wiz]

Why can't you (O.P.) see that you don't need anything except a direct connection between the "LIGHT" and the turn signal? Your description above shows this very clearly.

I think the description is a little incomplete - what I think they want is a dual function light.
ie One that works as a parking light, until the turn is active, in which case it follows the turn signal, until the turn signal ceases.

That's why a monostable is needed, because the dual-function feature is not possible with just gate logic.

[Obsidianxenon]

Everyone calm down...

what i want is:
- LIGHT ON when turn signal wire sends ON, and parking light is ON
- LIGHT OFF when turn signal wire sends OFF, and parking light is ON
- LIGHT ON when the turn signal wire sends ON, and parking light is OFF
- LIGHT OFF when the turn signal wire sends OFF, and parking light is OFF.

Just connect the light to the turn signal?

I am racking my brain trying to figure out how this is the eighteenth reply. A once-over of the truth table provided formed this conclusion in about 5 seconds?

[Someone]

Everyone calm down...

what i want is:
- LIGHT ON when turn signal wire sends ON, and parking light is ON
- LIGHT OFF when turn signal wire sends OFF, and parking light is ON
- LIGHT ON when the turn signal wire sends ON, and parking light is OFF
- LIGHT OFF when the turn signal wire sends OFF, and parking light is OFF.

Just connect the light to the turn signal?

I am racking my brain trying to figure out how this is the eighteenth reply. A once-over of the truth table provided formed this conclusion in about 5 seconds?

That truth table was changed since the original posting, and is still inconsistent with the descriptions and other truth tables.

[SparkyFX]

that you don't need anything except a direct connection between the "LIGHT" and the turn signal?

That would not switch the light off when the turn indicator goes off. Instead it would short "parking light on" and "turn signal off", probably blowing the fuse for the parking light.
You need logic in between.