A flashing LED stop light

I wanted to improve active safety when braking & increase the visibility of an additional LED stop-light : making the stop-light blinking at about 10 times per second makes it more eye-catching than a fixed light. This is not the usual slow-blinking light, the effect is more stroboscopic-like.
The LED stop-light is controlled by a simple electronic oscillator whose frequency may be choosen between 5Hz and 12Hz.

LED Pros :
• Monochromatic light, no need to use a color filter.
• Instant light-on / light-off : great for a stop light.
• No light-on intensity peak, like with a regular bulb.
• Very long lifetime : more than 100 000h (about 10 years !).
• Vibration-proof.
• High light efficiency, power consumption reduced by 10.
• Few heat is produced.
• May be directly controlled by an electronic circuit.

LEDs Cons :
• Lower light flux but improving fast.
• More expensive than bulbs.
• Require electronic control.
• Sensitive to over-voltage.

Schematic & board

This a very classic astable multi-vibrator based on the well-known NE555 (click image to enlarge).


Connectors on right side on the main schematic are connection to :
• Signal from stop light at rear connector (Stop)
• LEDs +
• LEDs -
• Neutral switch (under tank)
• Ground

On the optional part : a three position switch SW1 (ON/OFF/ON) to choose between :
• disconnected (middle position).
• strobe stoplight.
• standard stoplight.

Components :

IC1 : NE555 integrated circuit or CMOS equivalent 7555.
T1 : 2N1711 NPN transistor or equivalent (min 500mA/50v).
D1 : 1N4001 silicium rectifier 1A/50V or more.
C1 : 1µF polarized capacitor.
C2 : 10nF polyester capacitor.
VR1 : 47K variable resistor. Allow variable blinking frequency from 5 to 12Hz (ap).
R1 : 47K resistors (5%, 1/4w or more).
R2 : 1K resistors (5%, 1/4w or more).
R4 : 10K resistors (5%, 1/4w or more).

All components are standard and may be purchased at any component shop.
Active components have many equivalents.

Notes :
• Optional diode D1 allows disabling of the flashing mode when in neutral gear (generaly at a stoplight) to prevent the cager behind you getting nervous/blind/epileptic.
• No heat sink is required for the transistor as it works only in blocked/saturated mode.
• Frequency may be calculated like this : F(Hz) = 1.44 / ( C1 * ( R1 + 2 * ( R2 + VR1 ))
• With values given above the output signal cyclic ratio is 50%.
• All components are soldered on a 35x20mm PCB.
• Use a small plastic casing to preserve from moisture/vibrations.
• The harness connector for the rear light is located under the seat, on the left side.
• The harness connector for the neutral-gear is located under the tank (sky-blue wire connector).
• Overall cost : less than 3€ for the components, variable for the LED stoplight.

LEDs Stop Light

I bought a LED stoplight from a shop for about 6€. It's made with six clusters of four high-intensity red LEDs.
The supply voltage is 12v, peak current is about 200mA (a regular stop light bulb draws 2.0A). Actually average current will be only 100mA (it blinks !).
I've placed the light under the luggage carrier : there are two screw prints under it.
Two inox hex-screws will do the job.

Use only a true LED stoplight, not a scrapped car third stoplight, they are often made with small standard bulbs.
Such stoplights will burn the output transistor because of the high intensity they require (ten times more).


(image) (image)
(image) (image)


This device will likely NOT pass MOT, use it under your own responsibility. You may get trouble with the police using it - I didn't so far - that's why I recommend using it as an additional light.

Anyway, I've seen some high-end german cars using the same device - it also exists for some BMW bikes as optional part (very expensive).


Please enter your account details

Lost account details×

Enter your e-mail to receive your account details



Why sign-up ?

  • It's free but you can make a donation.
  • You gain access to fonctionalities otherwise not available.
  • It will boost your sex-appeal and allow you to time-travel.

How to sign-up ?

Username Required - 3 to 20 letters or digits
Password Required - 6 to 20 letters or digits
E-mail Required - enter a valid E-mail address

My account×

Modify my password

Current password

New password
Confirm new password

Modify my E-mail

Current E-mail

New E-mail
Confirm new E-mail

Delete my account

Current password

Add messageEdit message×
  • Your comments, feedback and suggestions are welcome !
  • Please use forums for any questions requiring a quick answer.
  • Your questions should relate to the TDM / XTZ / TRX only.
  • No links, ads, sales, doc requests. Thanx.
  • Edit your message then click the 'Ok' button.
  • An empty message will be deleted.
Name Required - 3 to 20 letters or digits
E-mail Optional - will be encrypted
Country Optional


Terms of Service and Privacy Policy×

Collection & use of your personal information

When registering to the site, you will be asked personnal informations such as your e-mail address, your country of origin, etc. This site will not provide or sell your personal information to a third party without your consent.

The site may collect information about your visit in order to operate and improve the site and the service it delivers. This includes the pages you view, the links you click and other actions taken in connection with the site. It also collect certain standard information that your browser sends to every website you visit, such as your IP address, browser type and language, access times and referring Web site addresses. Theses data is collected only for statistical usage and will not be used for any other purpose. This data is periodicaly erased (max 3 months).

Use of cookies

This site uses cookies to memorize your display language option and your session data. No personnal information is stored into the cookies. If your browser does not accept cookies, you will not be able to change language or open session.

Use of e-mail address

This site will not sell, lease or rent the e-mail you provide while registering or posting messages. E-mail addresses will not be used for any purpose other than sending you service e-mails : registering confirmation, updating your data or requiring a new password.


This site does not allow any messages containing :

  • Spam : repeated (commercial) messages.
  • Referral Programmes or Pyramid Schemes (links to websites through which you have a personal gain).
  • Rude and disrespectful behaviour, whether it is to members of this site or the staff of this site.
  • Language that is obscene, vulgar, sexually orientated, hateful, threatening or violate any laws.
  • Offerings of products (tangible or intangible) and services that you do not have legal disposition over.

This site reserves the right to edit or delete reactions and to ban any user violating the rules without notice. Freedom of speech is a right, however this does not mean we are obliged to publish your opinion.

This policy is subject to change without prior notice.




Send SMS×
Name Required - 3 to 20 letters or digits