Thoughts on interfacing piezo vibration sensor

piezo vibration sensor test with oscilloscope

Some time ago I purchased a MiniSense 100 Vibration sensor. Probably had some project in mind, but it happened that it dived into drawer among other “to do” things.  I thought it’s time to try a few things with it. Piezo sensor MiniSense 100 is very sensitive with pretty good frequency response and is linear (±1%). As you can see high sensitivity is achieved with a 0.3-gram inertial mass at the end of the film. As there is a hole in the mass you probably can screw in an additional mass and thus increase sensitivity even further. Probably there is no need to explain where such a sensor would be useful. These could be vibration/ motion sensors, impact sensors and other areas where motion and acceleration are involved. Usually, sensitivity is 1V/g. Where g, is standard gravity or also known as standard acceleration and due to free fall and is equal to 9.80665m/s2. As a mechanical device, it also has a resonant frequency at 75Hz. At this point, sensitivity reaches 5V/g.

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Building simple power supply from theory to working example

A power supply is an essential part of every electronic device. The whole system relies on it. If a power supply fails – device dies too, and there is a chance that sensitive parts may be damaged. Power supply solutions vary from device to device. They may work using different techniques depending on needs. Tim have described probably the simplest power supply solution which converts Alternating Current (AC) to Direct Current (DC). Supply circuit consists of well-known parts that are – transformer, which transforms voltage from 230V AC to 12VAC, them follows diode bridge rectifier, smoothing using large caps and regulation with standard 7805 voltage regulator. Such a solution proved itself in many designs. It is simple, cheap and builds fast. Tim put everything in short and informative post without overhead information. Following it, you will be able to construct a 5V DC power supply in an hour.  

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12V solar charger using LM317

[Alex] decided to build a solar charger for his car battery. He had an 18V solar panel able to provide up to 83mA. You cannot connect panel directly to the battery because charging voltage cannot exceed allowed safe limit and also solar panel may become a load for battery in dark time, and this way discharge it. So he ended up with simple circuit utilizing LM317 and couple resistors setting voltage so that battery would be charged at recommended 13.2V. To prevent back supply, a Schottky was used. Of course, it adds some voltage drop (0.7V worst case). This was taken into account while calculating voltage adjusts resistor divider. As a test [Alex] left solar charger for three days connected to his battery, and it charged up to 12.35V which is about 75% of capacity. Not bad at all.

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Adding self power down functionality to your devices

Power down feature is convenient on battery operated devices. For instance, most of the multimeters already have this feature allowing them to self turn off when there is no activity for some time. Check out this simple solution which uses a pair of FETs and resistor. It was initially made for the Atmega328 project because the author didn’t want to bother with AVR power down modes. Instead, he used this simple circuit. It can be used to turn the device on with the switch. This is where the P-FET part plays a role and turn off with N-FET. Turn Off signal wire comes from AVR pin market as 5. While the device is powered N-FET has to be on with high gate signal. When N-FET gate signal goes low device turns itself off. This can be used on any device where possible to get such signal conditions. Or use in microcontroller circuit by adding some delay count after inactivity.

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Avoid smoke with power protection circuit

When designing an electronic device you want to make sure that it won’t go in smoke under unexpected circumstances. You never know what may go wrong during the lifetime of the device especially if it is powered from mains. Jon Chandler made an excellent overview of standard and pretty simple power protection circuits that may help to avoid lots of trouble. The small circuit between your battery and device may protect it from mistakes like reverse power polarity. His lists start with a simple series diode which is cheap but may help protect from reverse polarity. Like any other, it has a downside – voltage drop (0.7V) that may be a pain for low voltage devices. The list continues with more smart solutions like Crowbar diode and fuse which avoids voltage drop but ends up with fuse blow on reverse voltage. Using MOSFET is a smarter way of protecting circuits. It gives a  smaller voltage drop – mV range with right MOSFET selected. This one is a common way used in many circuits. And of course, There are always specialized IC’s that provide way better protection. Like LTC4365 protects the circuit from reverse polarity but also from under and overvoltage.…

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Modeling of analog part for DDS3 signal generator

When building an AVR DDS2 signal generator, there were lots of discussions about signal conditioning in the analog part of the device. The first argument was that LM358 wasn’t the best choice for this purpose. Another one pointed to the sine wave that wasn’t smooth enough. As you can see, there are some dents on it. Other waveforms also are distorted especially when higher voltages are selected. This asks for a better analog part. Some people suggested to replace LM358 with OPA2134, but it seems to be quite an expensive choice. In my opinion low noise, a general-purpose op-amp can be great too. I’m going to give a try to Texas Instruments TL074 low noise op-amp. It is low power, high slew rate (13V/us) IC – almost five times faster than LM358 and for the same reasonable price.

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Multivibrator – back to basics

Multivibrator circuit is one of the first projects you start learning electronics. It is a beautiful circuit widely used for educational purposes and even in end projects as waveform generators. Lots of hobbyists grab a microcontroller/Arduino to blink LEDs. But using basic circuits like multivibrator may be cheaper, faster and even fun. [Ray] decided to go through multivibrator theory and explain its working in detail step by step. The circuit itself consists of two transistors, two capacitors, and four resistors. When powered, the circuit generates a square wave signal that can be used to flash LEDs or clock other circuits. You will get an intuition on what causes multivibrator continuously generate. Formulas allow calculating resistor and capacitor values for a particular frequency. Especially if you are a starter in electronics build one on a breadboard and do some experiments, why not to start with Christmas lights.

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