Vibration Transducer (DIY needed) - Page 1
Forum section: electronics / projects

author: metrologist
author_rank: Super Contributor
timestamp: January 20, 2017, 05:15:56 pm
content: I would like to detect a vibration, like one from the ticking of a clock or watch. Am I likely to have anything laying around that will work well for this?I was considering a PC microphone and using my DSO to trigger, but I think the mics I have require power, and a small speaker is not producing enough energy.

author: lilshawn
author_rank: Regular Contributor
timestamp: January 20, 2017, 06:30:48 pm
content: piezo maybe? not sure. a watch would have an incredibly small vibration that would almost be undetectable.what about disassembling a clockworks like so:http://www.ebay.co.uk/itm/HIGH-TORQUE-CLOCK-MECHANISM-SHORT-SPINDLE-8-INCH-FRENCH-SPADE-BLACK-HANDS-/281059839854then wiring directly to the pulse coil that triggers the clock "tick" motor?you can then have a nice pulse to count or what have you.does it specifically have to be a watch or clock? you can get RTC modules for arduinos.EDIT:haha! i just seen someone else doing something similar:https://www.eevblog.com/forum/projects/t81709/

author: metrologist
author_rank: Super Contributor
timestamp: January 20, 2017, 08:49:34 pm
content: I'm not building a clock, but I want to detect the vibration of a machine that is basically identical to a mechanical clock movement. There is a spring tooth on a gear, and I want to detect when the tooth strikes the gear. It's predictably cyclical. A bonus would be to also capture relative impact intensity.I can barely hear the sound if I am close, but I cannot quite feel it - that's just like a watch or small clock (actually my typical quartz clock ticks much louder as I can hear it 20 feet away.)I recall seeing what I think is a piezo buzzer - round flat copper disc with a whitish center. I thought it was a part or backing of something, so I do not know how to use it. There are two solder marks I think going to outer/inner regions.OK, I recall now I have a very small mic from a tablet. Maybe I could hot glue that to the case and connect the leads to my scope, or maybe I need an amplifier? Are those kid of mics typically passive?(BTW, I will build a GPSDO/clock, perhaps with a bit of a twist - but I did see that very small atomic clock chip known as the SA.45s Chip Size Atomic Clock (CSAC), it could be yours for just $1500).

author: lilshawn
author_rank: Regular Contributor
timestamp: January 20, 2017, 09:12:11 pm
content: yes a piezo speaker might do.piezo is a crystal at moves when electricity is applied, but also produces electricity when moved.

author: mmagin
author_rank: Frequent Contributor
timestamp: January 20, 2017, 09:44:32 pm
content: The commercial components for this are a 'arm' made of piezo material with a weight on the end. I imagine you could do somewhat similarly by taking a cheap piezo disc and gluing a tiny weight in the center, though the resonant frequency would still be a lot higher.

author: Gyro
author_rank: Super Contributor
timestamp: January 20, 2017, 09:47:41 pm
content: I recall seeing an electronic stetherscope type project of this type. It had the 'probe' (long thin flat head bolt) entering the end of the enclosure via a rubber gromet, head inside. A piezo element (of the type you described) was glued to the head of the bolt, copper disc 'ground' side, to avoid interference pickup. On top (bare side) of the element was glued a steel nut to provide some mass for the vibration to act against.With a high impedance cmos opamp type audio amplifier and headphones, the probe was apparently sensitive enough to hear a quartz watch stepper ticking.I suspect that epoxy would be the best adhesive to use as you would want rigid mechanical coupling.

author: metrologist
author_rank: Super Contributor
timestamp: January 20, 2017, 10:24:10 pm
content: My discs are about 30 mm diameter and I just saw an article where a guy soldered an LED to this kind of piezo and water drops would light the LED. I will try a simple test of just setting the piezo on the case and then set some weight on top of that and tap to see the response.I also just remembered I must have some strain gauges from a digital scale I took apart - they are glued to steel bars that would bend under the weight.I just found this - cool for a future project. Piezo-based surface scanning:https://dberard.com/home-built-stm/scan-head/

author: lilshawn
author_rank: Regular Contributor
timestamp: January 23, 2017, 07:28:56 pm
content: also realize...you are going to be down in the milivolts or possibly microvolts range of trying to see your "tick" air currents...construction crews working down the street...footsteps...temperature changes...earthquakes on the other side of the world...... are all going to come into play.

author: metrologist
author_rank: Super Contributor
timestamp: January 23, 2017, 08:36:13 pm
content: That's true. I used an amplified hearing aid - the kind one would clip to their shirt pocket and use a separate earpiece. It just amplifies sound and worked OK.