Brake Failure Indicator Using 555 Timer | DIY | Step by Step | How to




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Hi Today Instructable is very simple and easy to build Brake Failure Indicator Circuit
A Complete Step By Step Video Tutorial is also given in the video below.

Automobiles have been the primary mode of transportation for most of us and we depend on them for our day to day commute. Unfortunately there are lots of mishaps that could occur while driving an automobile and Brake Failures are one such case. Of course accidents cannot be avoided sometimes but they can sure be prevented by taking some preventive measures. In this project we will build a Circuit that can be attached to our Vehicles which will monitor the brake of our vehicle and provide us an audio-visual feedback if the brake fails.

Most economical vehicles depend on wire braking mechanism to apply brakes on the vehicle. This mechanism involves a Brake wire which runs from the brake lever to the braking mechanism set-up of the vehicle. It is this wire that gets pulled when we apply brakes to stop our vehicle. After a long use and tear these wires might get worn out and get cut at one point of time which eventually will cause a brake failure. So we will build a circuit that will monitor the continuity of this wire, the circuit will glow a green colour LED if everything is fine, but is the wire fails the circuit will blink a red colour LED also will beep a buzzer to alert the rider. Let us see how we can build this project...

Step 1: Harddware Required

  • Breadboard
  • 555 Timer IC
  • BC557 PNP Transistor
  • Red and Green Colour LED
  • 1uf and 0.1uf Capacitor
  • 1K and 440K resistors
  • Connecting wires
  • Buzzer
  • 9v Battery and Clip

Step 2: Circuit Diagram

As you can see this brake failure indicator circuit is very simple and can be easily built on a breadboard. The main components in this project are the 555 Timer and the BC557 PNP transistor. The 555 Timer operates in Astable mode to produce clock pulse and the BC557 PNP Transistor monitors the Brake wire and decides which led should glow.

555 Timers in Astable Mode:

The Astable mode in a 555 timer is mainly used for Blinking LEDs or to do some periodic Turn On and Turn off actions. In this project we have configures the Timer to work with 0.3Sec on time and 0.3sec Off time. The value of the resistors R1, R2 and capacitor C1 decides the on and off time of the Pulse produced. The formulas for calculating the same is given below.

T1 = 0.693(R1+R2).C1

T2 = 0.693*R2*C1

T = T1+T2

F = 1/T

Duty Cycle = T1/(T1+T2)

In our case the value for R1 = 1000ohm and R2=440000ohm and C1=0.000001F. So using these formulae we can calculate our values to be

So the output of the pulse should remain turned on for 0.305Sec and turned off for 0.304 seconds which is almost the same when analyzed on the graph below which was obtained with help of a Digital Storage oscilloscope.

The BS557 PNP transistor controls the LEDs and buzzer. When the Brake wire is in proper condition the base of this transistor is provided with 5V through a current limiting (R4) Resistor. This also drives the Green LED light and disconnects the Buzzer and Red LED from ground thus keeping it turned off.

When the break wire is cut the base of the BC557 is also cut and thus the Green LED is turned off and the Buzzer and Red LED are connected to ground. Since the positive end of Buzzer and LED is connected to the 3rd pin of 555 timers which is wired in Astable mode operation, they blink/beep based on the duration set by the above calculation.

Step 3: Working

Once the connection is made power the circuit, make sure the Brake cable (here I have used a normal green wire to represent the brake cable) is connected across the +5V and base of BC557 through a resistor as shown in the circuit.

If everything works as expected you should see the Green LED turned on and the Buzzer and Red Light Turned Off. Now, cut/remove the brake cable the Red LED and the Buzzer should start flashing as shown in the video below.

Hope you understood the project and got it working

Step 4: Datasheet



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4 Discussions

Kamali S

Question 15 days ago

Sir I'm doing this concept as mini project in my college ,I couldn't get that where to place resistor and where led positive and negative terminal is connected to buffer I'm literally confused so please give us the complete connection details sir please


Question 16 days ago on Step 3

In video you haven't mention which resistor is being places where.I cannot get it whether they are 1K or 440K resistor. I tried hard but couldn't make it even through circuit diagram. would be very grateful of you if you anyhow please mention. I have taken this project for my semester project. Please help ASAP

Rajdeep Barman

1 year ago

Good idea at all.
But, how much load current it can hold?


1 year ago


What netzener said, plus you need to swap Q1 emitter and collector for the circuit to be able to give any warning at all. As is, it can only extinguish the green LED.

While of absolutely no use in a car, it might have other applications to detect breaks in conducting stuff - _if_ you correct the schematic as devised.

As an aside note, never feed current through important parts of a car, whether wire or chassis. if at all avoidable, as it will increase rust and material migration!