Simple Piezo Vibration Sensor

A simple vibration sensor can be made from some PVC pipe components and a piezo – ceramic disc. This sensor is designed to be used with an oscilloscope. An oscilloscope is also necessary to test the operation of the completed sensor.

PARTS LIST:

1.) 0.75 inch PVC pipe plug. (Actual O.D. 1.050 inch)
2.) 0.5 inch length of 0.75 inch PVC pipe. (Actual O.D. 1.050 inch)
3.) 1.5 inch length of 0.156 inch O.D. plastic tubing. Evergreen Scale Models #225.
4.) 2.75 inch length of 0.093 O.D. plastic rod. Plastruct #90272 or equv.
5.) 0.5 oz sliding lead fishing weight.
6.) 1.062 inch (27mm) diameter piezo ceramic bender disc.
7.) 2 x 6 inch length of 30 or 32 awg insulated stranded wire. (see note below).

Note: The piezo bender disc can be purchased with or without attached wires.

CONSTRUCTION:

1.) Drill a 0.156 (5/32) inch hole in the center of the top of the pipe plug. Insert the 1.5 inch length of 0.156 inch plastic tubing into the plug until the end of the tube is about 0.5 inches above the top of the plug. Make sure the opposite end of the tube is centered in the open end of the pipe plug. Verify that the inside end of the tube does not extend past the end of the plug. Apply a small amount of cyanoacrylate glue at the joint to help hold it in place.

2.) Lightly sand the open end of the plug until it is completely flat. Remove any sanding dust. Clean the piezo bender with alcohol. Using a small amount of either cyanoacrylate or epoxie, glue the piezo bender to the bottom of the plug. Make sure that the side of the piezo with the silver-ceramic disk is on the outside.

3.) If the piezo bender does not have any wires attached, solder them on now. Use a minimum amount of heat as possible.

4.) Take the 0.5 inch length of 0.75 inch PVC pipe and file a shallow notch on one end. This is to provide clearance for the wires. Attach this piece using cyanoacrylate or epoxie to the exposed end of the piezo bender, locating the notch end over the wires.

5.) Verify that the 0.093 O.D. plastic rod slides freely inside the plastic tubing located on the top of the PVC plug. Using cyanoacrylate or epoxie, attach the lead fishing weight to one end of the 0.093 O.D. plastic rod. Once the glue has set, install the weight assembly into the plastic tubing on the top of the plug.

Construction is now complete.

VIBRATION SENSOR MAJOR COMPONENTS

 

COMPLETED VIBRATION SENSOR

 

TESTING:

The sensor can be tested by connecting it to a oscilloscope. Set the vertical volts/division to 200 mv/div or 500 mv/div.

Lightly move the lead weight up and down, allowing it to tap against the piezo bender. You should notice an output voltage being generated on the oscilloscope display.

In testing the sensor, I have found it to be very immune to electrical noise. To establish a base line output simply remove the lead weight from the sensor.

VIBRATION SENSOR AMPLIFER

Here is an adjustable gain AC coupled op amp based amplifier that can be used to amplify the output from the vibration sensor, up to about 10X. A small value capacitor, generally 1000pf or less, can be connected across Pin 1 and Pin 2 of the op amp to filter the high frequency component of the output.

Be sure to decouple the power supply input to the op amp by connecting a 0.1uF ceramic capacitor between Pin 4 and Pin 8 as close to the op amp as possible.

 

AMPLIFIER FOR USE WITH THE VIBRATION SENSOR

 

VIBRATION SENSOR EXAMPLES

The first two examples are of two cordless drills, a Makita Model 6041 and a much larger Black and Decker Model 2665.

The sensor was set on the handle of each drill and both drills were run at 450 RPM. The sensor amplifier was used and the gain setting was set identical for both.

VIBRATION SENSOR OUTPUT OF A MAKITA 6041 CORDLESS DRILL

 

VIBRATION SENSOR OUTPUT OF A BLACK & DECKER 2665 CORDLESS DRILL

 

The next two examples are with the sensor located on a hardwood surface. I lightly tapped the wood surface with my knuckle. In the first example, the sensor was located one inch away. In the second example, the sensor was located forty eight inches away. Note that in the second example where the sensor is located forty eight inches away, there is an apparent delay in the first waveform peak.

VIBRATION SOURCE ONE INCH FROM SENSOR

 

VIBRATION SOURCE FORTY EIGHT INCHES FROM SENSOR

 

Ya Verks Good!

 

 

 

 

 

 

 

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Bread Board Encoders

Using a normal size panel mount encoder when breadboarding a new circuit can be somewhat inconvenient at best since the solder lugs are mostly too large and usually in the wrong location.

Bourns makes a series of encoders that are very useful for prototyping circuits on the plastic breadboard strips that are in common use. The 16mm rotary encoders that Bourns manufacturers are low in cost and available from many different distributors in 12 or 24 pulses per revolution, with or without a momentary switch.

These encoders have just the right height and solder lug spacing to allow a simple straight inline 0.1 inch pin header to be soldered to the front of the solder lugs. Since the lugs are spaced on 5mm (0.2 inch) centers, I used a header with five pins, removing two of the unneeded pins.

On the encoder with the momentary switch, a 0.1 in pin header can be soldered to the opposite side of the input pins where the switch connections are located.

On the encoder without the switch, a piece of bare 22 awg wire was soldered to the mounting lugs on each side and the wire was then formed to provide support on the opposite side of the input pins.

Finally, a simple and inexpensive knob can be created for these encoders from a 0.5 inch piece of 3/16 inch silicone tubing.

 

 

ENCODER CONNECTIONS TO A MSP430 LAUNCHPAD

 

 

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Simple Square Wave Generator

This astable timer circuit is a simple square wave generator based on a CMOS version of the 555 timer that can maintain a nearly constant 50% duty cycle (+/- 1.0%) over a wide frequency range. This requires a transistor and a diode in addition to the other timing resistors and capacitor normally used.

HOW IT WORKS:

When the timer’s output is high, transistor (Q1) is forced into saturation (transistor on) by resistor (R2, 5.1k). This results in current passing through (Q1) and also (R1 + 3.3k resistor) to charge timing capacitor (C1).

When the output goes low, the discharge transistor, (open collector, internal to the 555 at pin 7) cuts off the base of Q1 (transistor off) and allows the timing capacitor to discharge through (R1 + 3.3k resistor) and diode (D1).

Since the resistance path is equal (or nearly so) in both the charging and discharging paths, the timing periods of both the high and low outputs are also equal.

COMPONENTS USED:

Although a regular bi-polar 555 timer can be used with good results at lower frequencies, I have found that using a CMOS 555 gives much better results over a wider and higher frequency range.

Transistor (Q1) can be any general purpose NPN transistor such as a 2N3904. Diode (D1) can be a 1N4148 or 1N914.

Resistor (R2) should be a value between 1.5k and 10k. The exact value of (R2) can be selected to give the best duty cycle symmetry with the timer running at maximum frequency. Maximum frequency is about 650 KHz (dependent on value of timing capacitor) .

The timing capacitor should be a quality Mica, Mylar or Tantalum type. Minimum timing capacitor value is about 100 pF.

 

SQUARE WAVE GENERATOR SCHEMATIC

 

OUTPUT AT 25 KHz

 

OUTPUT AT 250 KHz

 

 

 

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Bread Board Potentiometers

Using a potentiometer (other than a trim pot) with a 0.1 inch grid bread board can be difficult or inconvenient since in many cases the connecting lugs on the potentiometer usually do not match the 0.1 inch spacing on the bread board.

I have found one solution. The CTS 296 series single turn rotary potentiometers are reasonably priced, small in size and can be easily adapted to use on a bread board. These carbon composition potentiometers are 12mm in size and have a power rating of 0.15 watts.

They are available in 11 different resistance values from 500 ohms to 1meg ohm. The most commonly available have a linear output and a tolerance rating of +/- 20% . The vertical mount type are the ones I used. Matching knobs are also available for use with the knurled plastic shaft.

In order to adapt them to bread board use, I used four pins obtained from a 0.1 inch breakaway header. The pins were then soldered to the pins on the potentiometer. The potentiometer can now be easily plugged into the breadboard.

They seem to work quite well without further modification.

However, for additional support, a loop of 22 awg uninsulated wire can be soldered to the metal tab that is opposite the solder lugs. This loop of wire can then be cut to the correct length and inserted into the bread board along with the header pins.

 

 

 

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The Art of Electronics

The study of electronics is a very interesting and rewarding occupation for either the hobbyist or aspiring engineer.

Even the most casual hobbyist has easy access to thousands of low cost components, allowing anyone to take up the pursuit of electronics and advance it to any level of sophistication that he or she might desire – including as a rewarding career.

Back in the 70’s and 80’s, it would typically cost thousands of dollars to get started in the development of products that used a microprocessor – meaning that only large businesses could afford to do it. The use of a microprocessor also usually required the use of a number of support IC’s such as timers, port expanders, memory, and communication IC’s. The end result tended to be complicated and difficult to breadboard for testing purposes.

Today, just the opposite is true. Hundreds of low cost microcontrollers are available from a number of different manufacturers. For about ten dollars or so, one can purchase a complete development board that has an on board programmer and debugger and along with a free complete development environment (IDE) that can be downloaded to any laptop. (Some are code limited, but usually a generous limit.)

Sure, you would need to learn to program in assembly or C and also need a basic understanding of digital logic. However, the easy availability of the internet, for most people, allows the access to all kinds of electronics information, including electronic forums where you can ask others for help and even find complete programming examples to help you get started. Also, complete datasheets on practically any component you can imagine is usually just a few clicks away.

That said, it is always a good idea to have on hand a few reference books that pertain to your area of study.

In my opinion, one of the best must have books available for general electronics is:

The Art of Electronics (Third Edition) by Paul Horowitz and Winfield Hill.

This book, of about 1200 pages, contains an extensive amount of information on the basics of voltage, current, and resistance. Also, the theory behind and the use of components such as resistors, capacitors, inductors, diodes, bipolar and mosfet transistors, op-amps, voltage regulators, logic devices and much, much more.

The book also has numerous pictures and circuit examples that can be considered building blocks for your own projects. Most examples are simple and use components that are inexpensive and easily obtained. This allows one to breadboard and test the examples, providing an excellent way to learn and experiment with circuit theory.

All in all this is an excellent book for both the beginner and expert alike.

One Final Thought:

There seems to be a number of counterfeit and poorly produced copies of this book being sold, mostly online and at suspiciously low prices.

Please respect the enormous amount of effort over many years that the authors have put into creating this series of books starting with the first edition in the early 1980’s by purchasing only authorized and official versions.

 

 

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