Hello. I'm new to the forum. I'm trying to understand this circuit from a disc locker for scooters. It is powered by a pack of 6 LR44 batteries, it has a speaker, and I guess the black ic is an accelerometer. But, maybe you help me to understand it better?. Thanks in advance.

 

What is a disc locker for scooters?

 

Hello. This is it. It locks the wheel and makes a loud sound if moved.

 

Disc brake lock and alarm
It uses an accelerometer to detect motion and then activates a loud audible alarm by sending an AC signal to a piezoelectric transducer.

 

OK, I see the photo of the PCB, which has an unmarked 8-pin IC and three transistors with the numbers removed. The other side has an inductance and a polarized capacitor. And a piezo disk sounder.
So my guess is that it is a frequency swept oscillator.

 

OK, I see the photo of the PCB, which has an unmarked 8-pin IC and three transistors with the numbers removed. The other side has an inductance and a polarized capacitor. And a piezo disk sounder.
So my guess is that it is a frequency swept oscillator.

Hi. Thanks for your comments. How does the circuit detects the motion?. Is the black ic an accelerometer?.

 

I doubt that the IC is an accellerometer, although it might be. My guess is that the larger black item on the back side of the PCB is actually a mercury switch type of device. BUT, that is only a guess. There is a whole lot about the "Locker" that is not clear nor obvious.

 

I doubt that the IC is an accellerometer, although it might be. My guess is that the larger black item on the back side of the PCB is actually a mercury switch type of device. BUT, that is only a guess. There is a whole lot about the "Locker" that is not clear nor obvious.

Hello MisterBill2. Attached there is a pic of the black item in the back. I peel off the cover to check what is it. It looks like an inductor, not a mercury switch.

I check that the blue and yellow cables to the piezo speaker, while the red and black cables come from the batery. The switch that is activated with the lock is located on the black cable.

The locker part is just to active the switch. I removed the switch from the lock and active it manually, and it still is able to detect movement.

Any new idea how it can detect movement?

Thanks.

 

OK, that black module with the wire coil has another connection, so it might have a reed switch inside. And, if that piezo disc is not the noise maker, then it might be serving as a vibration sensor. Piezo devices do work both ways.

 

Is there a magnet near that inductor? Does the disc have slots or holes?

 

Is there a magnet near that inductor? Does the disc have slots or holes?

Hello Alex. No there is not magnet near the inductor. I tried using the screwdriver to look for any magnetic piece but no luck. There is a piezo speaker below the inductor (see attached pic), but is not magnetic, and its less loud than the main piezo speaker. The small one just makes some noise when you activate the circuit.

The disc is somewhat waterproof, so no slots or holes. Only the ones to remove the screwdriver.

 

That piezo disc inside is probably the vibration/motion sensor. I have seen that in some automotive alarm systems. They make a rugged and cheap sensor.

 

That piezo disc inside is probably the vibration/motion sensor. I have seen that in some automotive alarm systems. They make a rugged and cheap sensor.

Hello. MisterBill. I tried activating the circuit and just barely touching both piezo discs each time, and it activated the alarm without too much movement at all.

Do you have any schematics or link with info about these kind of alarms?

Thanks, Edwin.

 

I have no experience at all with alarms on 2-wheelers of any kind. I knew about the piezo device working as a sensor because I was given the alarm system that was removed when a friend upgraded (replaced)the alarm system of a VERY FAST used car they bought.
It had piezo vibration sensors. If the Disc-lock alarm works, why tear it apart???. Or do you want to make it much louder??

 

I have no experience at all with alarms on 2-wheelers of any kind. I knew about the piezo device working as a sensor because I was given the alarm system that was removed when a friend upgraded (replaced)the alarm system of a VERY FAST used car they bought.
It had piezo vibration sensors. If the Disc-lock alarm works, why tear it apart???. Or do you want to make it much louder??

Hello. I want to understand how it works as part of a project. How could it make it louder?

Thx.

 

How to make a piezoelectric transducer produce louder sound:

1. Increase the applied voltage.
2. Use a bridged driver to reverse the voltage.
3. Drive it at its natural resonance frequency.
4. Put a cylindrical tube made of cardboard or plastic over the transducer and tuned to the natural frequency.

 

There are definite limitations to the amount of energy that can be applied to transducers, especially to piezo-electric transducers. What happens is that the stress produced by the electric field is limited by the strength of the piezo portion, When it breaks, "the show is over." This means that there IS A POWER LIMIT!! Improving the acoustical coupling effectiveness can help, but the size increases and that may be a problem.
Adding an additional electronic sounder could be quite effective, but space on an electric bike is quite limited.

The alternative approaches that could work are specificly prohibited by this site and so I do not mention them.

 

There are definite limitations to the amount of energy that can be applied to transducers, especially to piezo-electric transducers. What happens is that the stress produced by the electric field is limited by the strength of the piezo portion, When it breaks, "the show is over." This means that there IS A POWER LIMIT!! Improving the acoustical coupling effectiveness can help, but the size increases and that may be a problem.
Adding an additional electronic sounder could be quite effective, but space on an electric bike is quite limited.

The alternative approaches that could work are specificly prohibited by this site and so I do not mention them.

Hello. Thanks guys for your help in understanding the circuit.

Best, Edwin.

 

IMO:

The inductor is just an inductor; no other function. With three leads, it could be part of a flyback autotransformer voltage-boosted driver for the piezo element.

The piezo is just a beeper element, nothing else. As a motion detector, it is not a good one; it produces zero output in two of the three motion axes.

There are too many parts on the bottom of the board for just a piezo driver. If you are sure there is no other motion sensor or electronic assembly elsewhere in the device, then the IC probably is the sensor. I'd look around for a mercury switch tilt detector.

ak

 

IMO:

The inductor is just an inductor; no other function. With three leads, it could be part of a flyback autotransformer voltage-boosted driver for the piezo element.

The piezo is just a beeper element, nothing else. As a motion detector, it is not a good one; it produces zero output in two of the three motion axes.

There are too many parts on the bottom of the board for just a piezo driver. If you are sure there is no other motion sensor or electronic assembly elsewhere in the device, then the IC probably is the sensor. I'd look around for a mercury switch tilt detector.

ak

Hello. Thanks for your message. Yes, it could be. The problem is that the IC has no name, then it is possible to find it easily if it has a motion detector or not. But, I just tapped the piezo speaker and it triggered the alarm right away. Maybe they used a cheap implementation for the motion detection instead of using a more expensive IC with a sensor inside.