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You are here: Home / Sensors and Detectors / Car Turn Signal Flasher Circuit with Lamp Malfunction Indicator

Car Turn Signal Flasher Circuit with Lamp Malfunction Indicator

Last Updated on June 29, 2020 by Swagatam 22 Comments

caution electricity can be dangerous

The post discusses an automotive/car turn signal indicator circuit idea with a built-in load malfunction indicator, meaning an additional LED lamp fitted on the dashboard which would warn if any of the side indicators went bad or fused. The idea was researched and requested by Mr. Abu-Hafss.

The Circuit Concept

I have found a transistor-based flasher including a relay, online

Physically, the circuit oscillates when a Load is connected across the pin "C" of the relay and earth. If the load is less than 100 Ohms the oscillation is significantly fast. And if the load is say about 1K the frequency is normal.

However, I could not understand the circuit nor it is simulating in LT Spice. Could you please explain me how the circuit is sensing the change in resistance of the load. And could you please make the simulation work.

OBJECTIVE:

To make a 555 based automotive turn signal flasher circuit which can detect lamp outage. If not possible with 555 then transistors may be considered.

CIRCUIT – A:

Above are the photos and schematic of the circuit. I have physically tested it. It also works on BC558/BC546.

With bench power supply of 12V-2A and load connected at pin (L) and (-), following is the behavior:

· No load, no oscillation

· Pin (L) and (-) shorted, very fast oscillation (relay sounds)

· Load 1 – 1.5K, normal oscillation (about 1.4Hz)

· Load increases, oscillation slows

· Load decreases, oscillation decreases

When using a car battery and 3 x 27W bulbs in parallel the circuit oscillates normally. Even, if a bulb is removed the frequency is unchanged. This means, this circuit does not detect lamp outage. However, the behavior of the circuit with a bench setup may give you some clue to my objective.

CIRCUIT - B

Yesterday, I came across this circuit which has a relay to detect load. I have not yet tested it. I hope this circuit might also help us. Maybe we can replace the relay with a transistor.

Thanks for your help.

Abu-Hafss

IC 555 based car turn signal indicator with pilot warning lamp:

The required circuit design which is shown below may be understood with the following points:

The IC 555 section is wired in the normal astable multivibrator whose  pulse rate at pin## can be adjusted with the help of the given 100K pot.

The two NPN transistors function as current sensor, and IC 555 reset controller.

When power is switched ON, the N/C contacts of the relay connect the turn signal lamps with the 12V supply.

The lamps light up and in the process draw the required amount of current via the Rx resistor.

The above current develops some voltage across Rx which triggers the left BC547 transistor and switches OFF the right BC547 transistor.

The above action resets the IC 555 so that it starts pulsing the relay and the connected lamps.

The LED at its N/O contacts also starts blinking in accordance indicating the correct presence of the lamps at the front and the rear side of the car.

Rx value must be selected such that it develops just sufficient voltage across it to trigger the transistor in response to current consumed by two lamps at the specified rates.

In case even one of the lamps malfunction, the voltage across Rx then wouldn't be high enough to trigger the transistor.

This situation would keep the entire circuit frozen, also keeping the warning LED shut off, providing the necessary malfunction indications to the driver.

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About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

Reader Interactions

Comments

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  1. Charles Biba says

    May 25, 2021

    Volvo in the 240 and 740 series cars used a much simpler system. Although they have been out of the production since 1993, I believe the cars were wired symmetrically (left/right) and critical external lighting was thus paired. Volvo had a sensor that measured power consumption left/right and front/back to make sure that if braking, the right-side amps = left side amps. Conversely, in the case of a signal light, that front turn signal amps = rear turn signal amps. They had a device under the font dash, driver side, that looked like a cylinder and had all the illumination circuits running through it. If power consumption didn’t match, it illuminated a “burned out bulb” indicator on the dashboard. Google “Volvo light bulb fail sensor”.

    Reply
  2. Patrick Puxley says

    February 10, 2020

    Thanks for the car flasher circuit. If the lamps are connected directly to earth as is normal in car indicator circuits, can the current sensing transistor (left hand) be connected at a location physically closer to the module, say, on the positive side of the lights before the indicator switch
    Would the circuit have to amended elsewhere
    Thanks
    Patrick

    Reply
    • Swagatam says

      February 10, 2020

      Hi, which circuit are you referring to? Is it the IC 555 one? Anyway yes you can do that without any amendments.

      Reply
      • Patrick Puxley says

        February 10, 2020

        Yes, the 555 circuit.
        Sorry, I saw your note about replying to the correct thread, but it isnt obviuos where the correct place is.
        Although I see the circuit has now been ammended somewhat from the one I was initially referring to, with a diode on the base of the LH BC547 (from a 22uF cap).
        Thanks for your reply

        Reply
        • Swagatam says

          February 10, 2020

          Yes you can place the current sensing stage near the lamps. I have improved the design slightly to ensure that the leftmost transistor remains switched ON even during the OFF periods and allows the 555 flasher to work normally.

          The note is to remind the users not to be off-topic while commenting. Your comment is perfectly related to the article topic so it’s more than fine.

          Reply
          • Patrick Puxley says

            February 11, 2020

            Hi
            I have the circuit working now as drawn, but I cant make it work with connection point for the sensing circuit (LH transistor) on the positive side of the switch (obviously!). The problem is that in a realworld motorcycle solution the lights go directly to earth on the negative side and the indicator toggle switch is physically remote from the flasher unit.
            Need to sense current flow in the positive side of the switch when the indicator switch is closed.
            This is what the physical layout is
            https://flic.kr/p/2irVTbc
            What am I missing?
            Thanks for your help, Im enjoying the learning. This is purely for interest ,because its possible to buy electronic flasher units quite reasonably……..its become a challenge!
            Patrick

            Reply
            • Swagatam says

              February 11, 2020

              Hi, thanks for the feedback,
              you can probably try modifying the design in the following manner:

              555 car flasher with lamp detector indicator

              Reply
              • Tom says

                June 16, 2022

                Hi
                Thanks for the flasher circuit. The 2 version looks like it would fit our classic car (lights are directly connected to ground). Unfortunately the values for the Cs above and below the BC557 are missing. What should they be?

                We are trying to retro firt that car wird led flashers. The only consume .4A. Is it correct that RX should be 3 Ohms in that case?

                Reply
                • Swagatam says

                  June 17, 2022

                  Hi, thanks, and glad you liked it. You can use 10uF/25V for both the capacitors. Yes the RX value should be 3 ohms for a 400mA load

                  Reply
            • Patrik Puxley says

              February 11, 2020

              Thanks. I sort of thought of that but was worried about how large the resistor would be, in series in the lamp circuit. Lamp circuit will be running at 4A (2x21W+5W =47W/12V= about 4A.) Is that right?

              Reply
              • Swagatam says

                February 11, 2020

                If the lamp current is 4 amps then the resistor can be approximately calculated using the following formula:

                Rx = 1.2 / 4 amps

                Reply
      • vincent says

        November 4, 2021

        instead of using 2 bc547 can you use 2 n channel motets

        Reply
        • Swagatam says

          November 5, 2021

          mosfets cannot be used here…

          Reply
  3. Swagatam says

    December 23, 2013

    It's my pleasure Abu-Hafss,

    In your circuit it could be because of the large value capacitor, not sure though? Otherwise your simulator could be giving wrongs results because any astable circuit may it be using an opamp or any other similar device will never produce an initial delay when switched ON.

    Reply
    • vincent says

      November 4, 2021

      if a lower value capacitor was used would that be ok

      Reply
      • Swagatam says

        November 5, 2021

        it will increase the flashing rate…

        Reply
  4. Abu-Hafss says

    December 22, 2013

    Hi Swagatam

    Thanks, your appreciation is really like an award for me 😉
    You may post it in your blog.

    The configuration of my op-amp oscillator is almost same as the one shown in figure 29. The only difference is that my design has extra resistor R4, which if removed does not result any change in the output.

    Reply
  5. Swagatam says

    December 20, 2013

    Hi Abu-Hafss,

    please try simulating the Fig29 "square wave oscilltor" shown the following datasheet of LM324, I am interested to see the simulation results:
    http://www.ti.com/lit/ds/symlink/lm124-n.pdf

    Reply
  6. Swagatam says

    December 20, 2013

    I'll check the opamp design and try to solve it, if possible…

    Reply
  7. Swagatam says

    December 20, 2013

    Hi Abu-Hafss,

    Great idea! This will surely work. I'll post it in my blog if you don't mind Mastermindji.

    Thanks for this idea!

    Reply
  8. Abu-Hafss says

    December 18, 2013

    Actually, I wanted to use a single IC for the circuit preferably LM324. Two op-amps for the lamp outage detection and one for astable oscillator. However, I faced a drawback.

    https://dl.dropboxusercontent.com/u/20969135/Op%20Amp%20Astable.gif

    Here is the sq. wave oscillator circuit with an op-amp, frequency 1.4Hz. But as you can see in the simulation, the oscillation starts after about 6.5s. Is there any way to avoid that?

    Reply
  9. Abu-Hafss says

    December 18, 2013

    Hi Swagatam

    First of all, please spare time to increase the headings of your so that it is easy to find some particular old posts. I understand it is time consuming but, it will quite helpful. It took me quite some time to locate this post. You can also increase one heading "Automotive projects".

    Ok, now here is the circuit which I designed for the car signal flasher with bulb outage detection function.

    https://dl.dropboxusercontent.com/u/20969135/Flasher.gif

    https://dl.dropboxusercontent.com/u/20969135/Flasher%20Circuit%20description.pdf

    I had completed this design long time ago but, forgot to report you Ustaad jee.

    Reply

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