Car Shock Sensor Module Review

Across the web, there are countless designs for shock/vibration sensors for automobile antitheft alarms, door/window break detector alarms, and almost any other security alarm you can think of. Many are very crude, using nothing more elaborate than a cheap vibration sensor and a circuit for notification, while others are very expensive.

A while ago, I was contacted by a reader about getting involved again with automobile security systems. I had thought about this in the past and built a few simple shock/vibration detector alarms with discrete electronics parts. Looking at those 90’s projects I found that there’s enough room to embed some new age electronics to make the idea more useful. Therefore, I thought I would give it a go.

The Device

To start off I needed to gear up an adaptive shock/vibration sensor switch to test out some ideas. I don’t like to use discrete components, so I got a little lazy started a lengthy Google search for prewired shock/vibration sensor kits. I came across another pretty cheap and elegant device described by its seller as “Car /Motorbike Vibration Sensor Module”!

These are the key technical parameters of the device, I copied from the seller’s page:

  • Name: Car vibration sensor module/Motorcycle shock sensor module
  • Rated Voltage: 12VDC
  • Working Voltage: 5-15VDC
  • Quiescent Current: ≤6mA
  • Output Current: ≤100mA (maximum load current)
  • Wire Color Code: White or Blue or Green: Signal output (one second pull-down signal in active state), Black: Ground, Red: Positive power supply

Sadly, my packet got lost in transit (or so it looks), and I ended up getting a refund for it. Because I wanted to try it and see what’s inside, I decided to order it again from another seller, and this time it managed to arrive. However, the device looked like a bit different from the image in the original listing, perhaps a clone of a model which was quite popular. Who knows?

Teardown

Now you can see the outside and inside of the device I got from the second seller.

As you might see, the major components in the circuit board are a piezoelectric element (piezoelectric disc), and an 8-pin chip. Piezoelectric discs are readily available, so serve as cheap noise makers in many projects. Many people, however, don’t realize they work in reverse, which is the basis of this design. Here, the piezoelectric disc is used as a tricky shock/vibration sensor, and the additional spring with a little mass at its hanging end makes it sensitive and more viable. The 8-pin chip is an op amp (LM358) that handles the output signals coming from the piezoelectric sensor to yield a sensible control signal output. The onboard potentiometer is included to set the detection sensitivity of the sensor electronics. Following is a closeup of the significant side of the printed circuit board.

Initially I tested the module with both 5V and 12VDC power supply inputs and it worked as promised by the seller. And it seems that in case of shock or vibration, its output signal changes from high – low for around one second, and that’s also indicated by the red LED. Rather annoyingly the output voltage is not at a ‘fixed’ level – it’s just a few volts below the actual Vcc level – that’s quite natural because there’s hardly any onboard voltage regulator or the like to give a stable voltage to the op amp chip. This will lead to some serious troubles while used to interface with a microcontroller – Beware!

Further, the sensitivity control potentiometer does not make sense as the device can catch a shock/vibration only when the potentiometer is knob is at its maximum travel, not a big issue though. I finally decided to capture its schematic. Here’s the reverse-engineered circuit diagram of the device devised by me but provided without any warranty. Likewise, values ​​of most components are not labeled here – that’s intentional because of certain restrictions, and sorry for that.

Reverse Engineering

Here, judging from the way the PCB legend looked, I presumed that orientation of the 1N4148(?) diode in the output section is wrong.

I soldered it again but now in the other way ie in the defined orientation so that I can add an external pull-up resistor to get a high output in idle state and a low output in active state – possibly better for low-voltage (3.3 V/5V) microcontroller interfacing even if the sensor device is powered by 12VDC power supply.

Set up for microcontroller designs

This is the proposed wiring diagram for the ‘hacked’ sensor box. Now the shock/vibration sensor is ready to work with any microcontroller – no matter how it’s powered in truth.

Now what? Simply connect to your favorite microcontroller, or to a ‘555’ timer circuit!

Just a side note: The BC847B (SMD code 1FW) is a general transistor for switching and amplifier applications. This NPN transistor has a maximum collector-emitter voltage (Vceo) of 45V, and collector current (Ic) of 100mA (www.taitroncomponents.com).

A simple build trick

Okay, so maybe you don’t want to use a microcontroller? Here’s another simple idea. I added a common active piezo-buzzer between the vcc and out pins of the 3-pin connector, so in active state I’ve got a ‘one second long’ visual and audio ‘shock/vibration’ alert – decent for a small tingle !

Perhaps you’d like to put an electromagnetic relay there to operate a beefy load, a motor horn for example, but see, you’ll then need a low-current type relay to play along with the idea. You can however tweak the internal output circuitry through bypassing the 100Ω resistor and the 1N4148 diode (see below) as those funny parts are not essential here in this non-uC application. Once you know what you are doing, you know when it’s all right to deviate from the rules!

Quick Revision

Car shock sensors, designed to detect vibrations caused by motion of the vehicle, protects the windows and wheels of your car. Breaking any glass plane cause shock waves to pass through the metal structure of the vehicle. Jacking up a car and loosening wheel nuts will also cause movement. The car shock sensor sends a signal to the attached security alarm when either event occurs.

As presented here, output stage of the car shock/vibration sensor device can be used to interface with a variety of electronic circuits. Once again notice that its internal transistor is off in idle state. But when the piezoelectric disc detects a shock/vibration, the small voltage is processed by the op amp, and the transistor is switched on zeroing the final output at the 3-wire connector. However, the final output you get from these unbranded devices can vary significantly. So first off get into the enclosure, watch over the electronics – the output circuitry in particular, and do the simple hack(s) if necessary.

Time for play

These little car shock sensors are very cheap and can be found on many places. On the Internet you can buy them on eBay, Aliexpress, Banggood, and many other sites. They could be hacked simply to work as a compact shock/vibration sensor in your next security alarm project (with or without a microcontroller), right?

Nowadays, more sensitive and efficient pendulum and cantilever shock/vibration sensors can be made from hardware found in almost any storefront. You can also build improved devices based on angular transducers, where the system is managed by a built-in microprocessor which automatically adapts to the position of the vehicle. In such a commercial device, angular variations are analyzed, and any minor disturbances are simply ignored. When a genuine third-party intervention is detected the device wakes up to raise an alert.

Remember there are many things that can cause the car shock sensor to vibrate in real world. The mounting location of the shock sensor in a car is also a major factor. In theory, the best location for one is the center of the vehicle so it is not biased to one side.

Going Further…

Next thing on my to-do-list is the design and development of a simple impact sensor based on a special magnetic vibration/shock sensor. The proposed magnetic sensor (see below) is simply a magnet held by an elastic band which is suspended close to a coil. When the magnet vibrates it induces electricity in the coil. This, in turn triggers the alarm electronics to go off. These sensors need a bit more complex electronics so are not going to make sense unless you are into it. You can do your own homework if you really are interested. Intelligent hey!

Ha Ha, I’m not the first one working on this idea. See the forerunner – another “Magnetic Vibration Sensor Module” found in the market!

Credits & References

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