"zero power" g sensing trigger?? - Page 1
Forum section: electronics / projects

author: max_torque
author_rank: Super Contributor
timestamp: May 03, 2023, 02:47:50 pm
content: I have a large (500kg) sensitive product that when it is running has an internal 3 axis accelerometer that measures the acceleration that the device is subjected too. Should excessive accel be determined then the device puts itself into a "safe" mode.However, during shipping and storage the device is not powered but i'd like to know if during that time someone has been, er, a bit careless with itSo, what i would like is a simple, ideally pcb based, G sensing "switch" that requires no power to run (or such a tiny amount of power it can run from say either a supercap or lithium primary cell etc0 and that switch should be fairly easy to set so as to vary it's sensitivity to tripping, and once it has tripped, it does something that can be sensed the next time the device is powered up, and the device can refuse to work..Ideas so far are a piezo sounder, used as a basic acceleration sensor, that at a certain level of g fires the gate of a mosfet, which discharges a cap or lithium cell across something that can be "one time" blown, ie a resistor, or perhaps zener, or even the base of a small transitor, and then when the device is powered, it can apply some sort of signal to that sensing element to determine if it has been blown during the power off time.Hopefully i've explained the problem well enough for people to have some ideas? I want to try to avoid anything too mechanical (ie balls on springs, magnets, trembler arms etc etc) It also should be capable of being "disabled" when the power is on to the unit, so it cannot be accidentally tripped during actual use of the device.a single axis of g sensing is acceptable as long as the device is small / cheap enough for us to fit one per axis (ie 3) if required, which also allows us to have different tripping sensitivites in each axis.Other ideas are using some form of break glass dye device (already available for shipping / package monitoring) that some sort of LED/LDD could somehow "read" when it is powered up etc??Any other great ideas anyone??

author: langwadt
author_rank: Super Contributor
timestamp: May 03, 2023, 03:43:38 pm
content: http://stop-drop.com/store.html#!/Stop-Drop-Impact-Sensor/p/32798560/category=7134026 ?

author: jwet
author_rank: Frequent Contributor
timestamp: May 03, 2023, 03:59:31 pm
content: There are also mechanical only caged ball sensors that keep a steel ball suspended between two springs. 1 or 2 axis and a bunch of G ratings-cheap. Google "shock fuse" or "protect a pak" or "impact o graph". The have a wide range of this stuff and have been around for a long time. A fancy shipper will provide them as an option.

author: max_torque
author_rank: Super Contributor
timestamp: May 03, 2023, 05:32:11 pm
content: Quote from: langwadt on May 03, 2023, 03:43:38 pmThe problem with this sort of (easy to make) device is that once triggered the battery in it goes flat! Ok for shipping stuff when delivery time could be a few weeks at most, but i have a shelf life of up to a year to try to hold the "ive been dropped" state for.There are plenty of ball on spring type trembler switches that could be used with a small micro. I guess one could use an interupt on the "too much g signal" to wake the micro, write "oh crap i've been dropped" to eeprom or flash memory, then go back to sleep. That would be fairly easy to do and with a small coil cell battery could have a very long shelf life?

author: langwadt
author_rank: Super Contributor
timestamp: May 03, 2023, 06:29:09 pm
content: Quote from: max_torque on May 03, 2023, 05:32:11 pmmany an mcu with an RTC can maintain time and a few bytes of ram for a few uA, it could probably last years on a coincell

author: m98
author_rank: Frequent Contributor
timestamp: May 03, 2023, 10:18:52 pm
content: Modern accelerometers have really advanced event detection, use something like the LIS2DUXS12TR to wake up your micro.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 06, 2023, 07:43:29 pm
content: There are also g-sensors for shipping without any electronics. I think they work of something like a small weight suspended by a few strings, and one of the strings break if the sensor is subjected to too high G-forces. With such a sensor, you have no idea of when the excessive G-force occurred of course.