Post by thread:[PIC]: Electrolytic tilt sensor: build ?

Hi, I am interested in integrating a $SUBJ very tightly with a very small board. That means build it, as all parts are too big for this. I am thinking of the halfcircle-shaped cavity differential type, built between a sandwich of 3 FR4 boards, top and bottom 0.5mm and middle (spacer with halfmoon/halfcircle channel machined into it) 1.5mm with no traces. The electrodes will be etched directly into the top and bottom thin boards. This and running the hot electrode off the PIC's clock through a buffer and using two rectifying detectors to feed two AD channels is the easy part. Now what juice do I use ? Mercury is very tempting but I'd rather not. Some sort of electrolyte is needed that will not foam and not stick to the walls too much. High specific gravity is nice. Stopping short of 'milking' a large electrolytic capacitor for the prototypes, what could I use ? Salt water should work, some sort of light oil seeded with something conductive ? Come to think of it, some blood plasma will do fine according to specs <g>. Peter -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

At 10:41 PM 10/24/00 +0200, you wrote: >to the walls too much. High specific gravity is nice. Stopping short of >'milking' a large electrolytic capacitor for the prototypes, what could I >use ? Salt water should work, some sort of light oil seeded with something >conductive ? Come to think of it, some blood plasma will do fine >according to specs <g>. Suggest something along the lines of kerosene (the North American kerosene). I think you should avoid ionic liquids like the plague. Best regards, =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" .....speffKILLspam@spam@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestKILLspammitvma.mit.edu

Hi Peter, Normaly you would use oil as the dialectric, chose a thicknes of oil that suits the responce speed you require. The closer the plates the higher the capacitance, too close and you may have problems with capillary action. You Can't use Mercury as a dialectric in a capacitor, the plates would be shorted all the time (good tilt switch). Regards Peter W. >>> "Peter L. Peres" <.....plpKILLspam.....ACTCOM.CO.IL> 10/25 6:11 AM >>> Hi, I am interested in integrating a $SUBJ very tightly with a very small board. That means build it, as all parts are too big for this. I am thinking of the halfcircle-shaped cavity differential type, built between a sandwich of 3 FR4 boards, top and bottom 0.5mm and middle (spacer with halfmoon/halfcircle channel machined into it) 1.5mm with no traces. The electrodes will be etched directly into the top and bottom thin boards. This and running the hot electrode off the PIC's clock through a buffer and using two rectifying detectors to feed two AD channels is the easy part. Now what juice do I use ? Mercury is very tempting but I'd rather not. Some sort of electrolyte is needed that will not foam and not stick to the walls too much. High specific gravity is nice. Stopping short of 'milking' a large electrolytic capacitor for the prototypes, what could I use ? Salt water should work, some sort of light oil seeded with something conductive ? Come to think of it, some blood plasma will do fine according to specs <g>. Peter -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

Hi Well I've tried to build one of these things and... a) What you fill it with depends on how you expect it to work. From what I've seen you basically have two choices. One is to use some kind of substance that does allow a current to flow through it and then make sure you use an equal AC current to ensure that you don't get all sorts of odd things happen to the stuff! Second is to use some sort of liquid that does not conduct and use a purely capacitive effect. My understanding is that most of the commercial sensors use the first of these options (this is the way I've tried doing things). b) I've seen articles that use water (possibly de-ionised not really sure), with a small amount of alcohol added to help prevent the surface tension problems. c) The big problems I had was getting the damn thing sealed up (you have to have a really, really good seal otherwise they eventually dry out. Most of the things you would like to use as the liquid have a nasty habit of screwing up most of the things you would like to use to seal them! e) Sounds like you are going to have a very small space. I would take great care with checking that the surface tension/capillary action problems do not screw you up. f) Check the resolution you need most of the commercial units I've seen get better resolution by going from a wider gap between the electrodes. Sounds like you won't have that option! Good Luck I spent ages trying to do this and then gave up and got a commercial part (but then the facilities (and skill) I had available may not be anything like yours!). Let us know how you get on. Andy {Original Message removed}

Andy Shaw wrote: {Quote hidden}> > Hi Well I've tried to build one of these things and... > a) What you fill it with depends on how you expect it to work. From what > I've seen you basically have two choices. One is to use some kind of > substance that does allow a current to flow through it and then make sure > you use an equal AC current to ensure that you don't get all sorts of odd > things happen to the stuff! Second is to use some sort of liquid that does > not conduct and use a purely capacitive effect. My understanding is that > most of the commercial sensors use the first of these options (this is the > way I've tried doing things). > b) I've seen articles that use water (possibly de-ionised not really sure), > with a small amount of alcohol added to help prevent the surface tension > problems. > c) The big problems I had was getting the damn thing sealed up (you have to > have a really, really good seal otherwise they eventually dry out. Most of > the things you would like to use as the liquid have a nasty habit of > screwing up most of the things you would like to use to seal them! > e) Sounds like you are going to have a very small space. I would take great > care with checking that the surface tension/capillary action problems do not > screw you up. > f) Check the resolution you need most of the commercial units I've seen get > better resolution by going from a wider gap between the electrodes. Sounds > like you won't have that option! > > Good Luck I spent ages trying to do this and then gave up and got a > commercial part (but then the facilities (and skill) I had available may not > be anything like yours!). Let us know how you get on. > > Andy Hi guys, I am having difficulty understanding why this is the best way to meaure tilt, etc? Using ac, variable capacitance, etc etc? Why not get a little container with a translucent liquid, and two simple cheap opto trans/rec pairs. As the tilt changes the liquid thickness between each pair would change, changing the light amount getting through. The transmitter is just the leds and a power source. The receiver can tie the optodiodes straight into the analogue pins on a PIC with a pull up resistor and for almost zero parts count you have a good reliable analogue tilt sensor. But if you start using ac and liquids you get problems like corrosion, dissimilar metals reacting, salts from electrolysis, etc etc. What is the benefit of the ac driven system? -Roman -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:","[SX]:","[AVR]:" =uP ONLY! "[EE]:","[OT]:" =Other "[BUY]:","[AD]:" =Ads

On Tue, 24 Oct 2000 09:53:08 +0100, you wrote: >Hi Well I've tried to build one of these things and... >a) What you fill it with depends on how you expect it to work. From what >I've seen you basically have two choices. One is to use some kind of >substance that does allow a current to flow through it and then make sure >you use an equal AC current to ensure that you don't get all sorts of odd >things happen to the stuff! Second is to use some sort of liquid that does >not conduct and use a purely capacitive effect. ..or presumably use a conductive liquid and put the electrodes outside the enclosure - on the other side of the PCB in this case. This may also simplify sealing as the inside PCB surfaces will be level. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:","[SX]:","[AVR]:"

Roman said; >Why not get a little container with a translucent liquid, and >two simple cheap opto trans/rec pairs. As the tilt changes the interestingly enough there is a playstation controller called the airpad that uses a similar technique. it was designed in the uk too, which makes it even cooler. oh and judging from this link: http://www.psxnation.com/news/120799b.shtml it uses a scenix too... wonder if the designers are on this list ? hellllloooooo! Regards, Simon -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:","[SX]:","[AVR]:" =uP ONLY! "[EE]:","[OT]:" =Other "[BUY]:","[AD]:" =Ads

> Roman said; > > >Why not get a little container with a translucent liquid, and > >two simple cheap opto trans/rec pairs. As the tilt changes the > > interestingly enough there is a playstation controller called the airpad that uses a similar > technique. it was designed in the uk too, which makes it even cooler. oh and judging from this link: > http://www.psxnation.com/news/120799b.shtml > it uses a scenix too... wonder if the designers are on this list ? hellllloooooo! > > Regards, > Simon > Sounds like these will be wonderfully hackable. Hopefully these won't sell well and we can purchase them at or below the manufacturing cost a la the US $9.95 gameboy camera. Roger Kadau netServ -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:","[SX]:","[AVR]:" =uP ONLY! "[EE]:","[OT]:" =Other "[BUY]:","[AD]:" =Ads

Thank you for the many ideas. Maybe I did not make myself very clear, the sensor is to be capacitive. No metal will touch the fluid, which will be conductive. The reason for using a conductive fluid in a capacitive sensor is the 5:1 or better output signal capability vs. moving dielectric types. With the materials stated in the previous posting the ratio will be about 2.5:1. The ratio measures capacitance ratio in a unit area of the sensor with vs. without moving armature (conductive liquid). The optical sensor is interesting but it is too bulky and has the same sloshing problems that a liquid type capacitive sensor has (plus everything must be transparent). It is also affected by foaming and film formation more than the capacitive type. Plus the LEDs and diodes cost money. A nice optical sensor is based on an optical fiber that is bent or deformed (across its section) by a weight. All this is capsulated in rubber. The system measures fiber attenuation vs. bending. It doubles as an accelerometer. Peter -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 10:40 PM 10/26/00 +0200, you wrote: >Thank you for the many ideas. Maybe I did not make myself very clear, the >sensor is to be capacitive. No metal will touch the fluid, which will be >conductive. The reason for using a conductive fluid in a capacitive sensor >is the 5:1 or better output signal capability vs. moving dielectric types. >With the materials stated in the previous posting the ratio will be about >2.5:1. The ratio measures capacitance ratio in a unit area of the sensor >with vs. without moving armature (conductive liquid). Ok, take a test tube (Or U shaped tube, depending on what response you want). Apply copper foil along 1/2 of the tube. Slit the foil lengthways, and slit one section of that in the middle. ----------------------- "Common" ----------- ----------- "A" and "B" Add mercury or other conductive liquid to the tube. Inject a signal to "common" and measure the relative amplitudes of that signal at "A" and "B". You could add a second liquid to control splash, and speed of response (remember the "prell" commercials?) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Hi, Sounds like you have done a fair amount of work with tilt sensing. Have you come accross anything in particular for measureing YAW? Gravitiy only goes so far :) I'm interested in tracking a rotation around the Z axis along with pitch, and roll... In particular i'm interested in small portable type of sensors. Things a person could carry. THANX _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. Share information about yourself, create your own public profile at http://profiles.msn.com. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>I'm interested in tracking a rotation around the Z axis along with pitch, >and roll... >In particular i'm interested in small portable type of sensors. Things a >person could carry. I would have thought this was an ideal application for an ADXL202 series accelerometer. It would require a bit of computing effort to sort out the rotation angle from the acceleration, bit otherwise you would have a hard job to find anything smaller and lighter than an ADXL202E. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

You might also have a job finding ADXL202's, if anybody knows of a good source for a few hundred, preferably of the new package type, please let me know. We are having supply problems Martin {Quote hidden}> >I'm interested in tracking a rotation around the Z axis along with pitch, > >and roll... > >In particular i'm interested in small portable type of sensors. Things a > >person could carry. > > I would have thought this was an ideal application for an ADXL202 series accelerometer. It would require a bit of computing effort to sort out the rotation angle from the acceleration, bit otherwise you would have a hard job to find anything smaller and lighter than an ADXL202E. > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

>pitch yaw and Z axis (i.e. bearing) You mean like a gyro platform and a compass ? If you like to carry heavy things wire a surplus aircraft gyro and a compass into a box with a battery and you have what you want. Both have electrical outputs which can be logged by most better data loggers (with analog inputs). Oh and you need a clock too, because the gyros walk around in 24 hrs. If you don't like to carry heavy things then start on the long path of integrated navigation computers. These have interesting applications, such as making cruise missiles, and they are neither cheap to buy not easy to make. Not that I've made any. Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.