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| | <!-- ____________________ --> | | <!-- ____________________ --> |
| − | ==Question 8 ==
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| − | ==USB Modem run on Arduino ==
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| − | 29th August 2012<br />
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| − | I have a Huewai E160E USB Modem which I want to use to send sms messages from an Arduino board all operating as a stand alone system.
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| − | When these devices are used in computers a program called "modeswitch" is used to switch the modem between its three states .<br />
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| − | Those states are :-<br />
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| − | 1/ The SD Storage memory card facility<br />
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| − | 2/ The CD area that hold installation programs and<br />
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| − | 3/ The modem proper.<br />
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| − | The arduino chip does not have the memory resources to hold the "modeswitch" program and hold my program. I am able to switch off the CD area by sending the right command to it and it stays off permanently but I don't seem to be able to disable the SD card memory area permanently so that only the modem is available on power up.<br />
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| − | Does anybody know if this can be done and if so how?<br />
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| − | Additionally does anyone know how I could address the SD card memory from the Arduino and perhaps hold the "modeswitch" program there and run it from there when needed by the Arduino . What would the C++ code be or look like to address this area?<br />
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| | == Question 7 == | | == Question 7 == |
| − | == accelerometers on a wheel ==
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| | Hello, | | Hello, |
| | I'm building a small machine that includes a wheel mounted on an axle. Four accelerometers will be attached to the wheel; equally spaced around the perimeter and diametrically opposite. The object is to sum the analog output signals to cancel out gravity but to measure simply the acceleration/decelaration of the speed of rotation. My main concern is how do I wire up the accelerometers? I would like to avoid slip rings if possible (the axle is 6mm diameter). Is there a simple RF emmitter/receiver available in an IC package capable of tramitting the analog output (+/-3v) from the accelerometer? | | I'm building a small machine that includes a wheel mounted on an axle. Four accelerometers will be attached to the wheel; equally spaced around the perimeter and diametrically opposite. The object is to sum the analog output signals to cancel out gravity but to measure simply the acceleration/decelaration of the speed of rotation. My main concern is how do I wire up the accelerometers? I would like to avoid slip rings if possible (the axle is 6mm diameter). Is there a simple RF emmitter/receiver available in an IC package capable of tramitting the analog output (+/-3v) from the accelerometer? |
| | Thanks for any suggestions offered. | | Thanks for any suggestions offered. |
| | Vielle568 | | Vielle568 |
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| − | EDIT:
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| − | Thanks for all the feedback; very useful.
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| − | In reference to answer 2 and concerning my project:
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| − | What am I trying to do exactly? Well I am an instrument maker and I've been experimenting with electric hurdy-gurdies. The instrument functions by turning a crank and a wooden wheel rubs against the stings like a circular bow. One sting creates a rythmn when the crank is accelerated and I want to replace this string with electronics. In other words I want some kind of sensor that'll capture the acceleration pulses of the wheel that correspond to the rythmn. I want to use this signal to activate either an analog swith or an envelope follower to control an effect for the rythmn.
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| − | The wheel is about 7" diameter and mounted on a steel axle in the heart of the instrument; it is not too easy to access but it is removable and sensors can be attached to the side faces without any problem. Use of slip rings makes installation difficult and transmission by radio would be a better solution. The receiver can be housed in the instrument's body beside the wheel with the other electronics.
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| − | Maybe a gyro would be a better idea than two or more accelerometers but I remember reading on the spec sheet that gyros had a limited range of degrees. Maybe this isn't always the case? Could a gyro continuously monitor rotational speed on a rotating wheel or would this be impossible?
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| − | [[File:VIELLE9.JPG]]
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| − | The current system uses a series of small holes around the wheel rim and a small laser; a frequency to voltage converter sets a voltage level for the wheel speed and a comparator trips when the voltage passes a reference level; the output then triggers the analog switch. It works OK but the circuit response is too slow for fast passages of music.
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| − | Vielle568
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| − | === Answer 1 ===
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| − | Literal answer:
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| − | There are several ways to power electronic devices while they are spinning.
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| − | The most popular are "slip rings" and "mount a battery so it spins with the rest of the electronics".
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| − | See "[[POV display]]" and [http://electronics.stackexchange.com/questions/12704/electrified-vertical-mounted-rotary-joint-questions "Electrified Vertical mounted rotary joint questions"]
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| − | for some examples.
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| − | Perhaps someone will write a "[[spinning electronics]]" page someday to list other ways to transfer power.
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| − | Once you have power to your rotating platform,
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| − | I'm pretty sure you can power the accelerometers using the standard circuit in the data sheet for that particular accelerometer.
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| − | Once your accelerometers have power and are driving their output pin,
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| − | there's a simple, low-cost circuit called a "op-amp summer" to sum the signals from two opposing accelerometers, to get the radial acceleration with gravity canceled out.
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| − | There's a [http://en.wikibooks.org/wiki/Electronics/Op-Amps#Quick_Design_Process op-amp quick design process].
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| − | I suppose if you were curious you could plow through the "summer" section of the "[[OpAmp Links]]" page, although they generally make it sound far more complicated than it really is.
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| − | You're going to have various mis-matches from: accelerometers positioned not quite opposite the center of rotation; positioned not quite the same distances from the center of rotation; the accelerometers may have slightly different offset/scale errors; the resistors used to build the summer have small resistance errors; all of the above may vary with temperature, so even if you calibrate and cancel them all out at one temperature, they may no longer cancel out at a different temperature, etc.
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| − | So gravity won't be completely cancelled out, but I think you'll be able to get close enough -- perhaps after a bit of tweaking and tuning.
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| − | Since I don't know much about transmitting analog values directly,
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| − | I might consider feeding the analog sum signal into a microcontroller (either directly, with a microcontroller with a built-in ADC, or indirectly through a peripheral ADC chip), then somehow transmit that digital data through visible light, infrared light, or radio.
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| − | There are many small, low-power microcontrollers that can easily be mounted on a rotating platform and powered by a small coin cell.
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| − | Perhaps a [http://jeelabs.com/products/jeenode JeeNode] mounted on the rotating platform, to digitize the signal and transmit it wirelessly, then use a [http://jeelabs.com/products/jeelink JeeLink] to receive that wireless signal and pipe it into the USB port of a PC.
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| − | Or perhaps a couple of [[Arduino Links | Arduino]] boards, each one with an XBee wireless board plugged into a [http://www.arduino.cc/playground/Shields/Xbee01 XBee Shield].
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| − | Or perhaps another [http://www.glacialwanderer.com/hobbyrobotics/?p=291 "Cheap Arduino Wireless Communications"] approach.
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| − | [http://www.seeedstudio.com/wiki/index.php?title=RFbee_V1.1_-_Wireless_Arduino_compatible_node RFbee] apparently has a (Arduino-compatible) microcontroller and all the wireless communication stuff on a single board.
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| − | Various other wireless and infrared communication techniques [http://www.arduino.cc/playground/Main/InterfacingWithHardware#wireless have Arduino libraries available].
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| − | === Answer 2 ===
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| − | Less literal answer:
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| − | What exactly is it you are trying to do?
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| − | If you want to measure the acceleration due to the spinning at some point a distance R away from the center of rotation,
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| − | perhaps a simpler and cheaper approach would be:
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| − | * install a single gyro. (There's some low-cost gyros mentioned on the [[Multi-rotor]] page. You can mount it anywhere on the spinning platform; it doesn't have to be exactly R from the center of rotation.
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| − | * Use the gyro to measure the rotation rate "w" in radians/second. (You might have to convert from revolutions/minute, revolutions/second, or whatever weird units that particular gyro uses).
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| − | * Assume that a few "laws of physics" supported by centuries of experiments will continue to hold, and calculate the acceleration due to spinning as R*w^2. That acceleration is sometimes called a "[http://en.wikipedia.org/wiki/Centrifugal_force_%28rotating_reference_frame%29 centrifugal force]".
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| − | == Question 6 ==
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| − | Hello I have a problem with a temperature sensor it has 1 Mohm of resistance at ambient temperature and according with the specification the value has to be 2 Kohm, I think that the circuit is open but I do not why, do you Know any reason for open circuits, or for the sensors failure.
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| − | Measuring 1 Mohm or more on a 2 pin temperature sensor such as a [http://en.wikipedia.org/wiki/Thermistor thermistor] or a [http://en.wikipedia.org/wiki/Resistance_thermometer resistance temperature detector]?
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| − | Then it's probably permanently destroyed.
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| − | Sorry.
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| − | I usually destroy things by putting too high voltage -- now I know 120 V is too high :-).
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| − | I suppose it's also possible it failed from over-temperature or other stress.
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| − | --[[User:DavidCary|DavidCary]] 17:05, 30 August 2008 (PDT)
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| | == Question 5 == | | == Question 5 == |
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| | [[russ_hensel]], --[[User:DavidCary|DavidCary]] 12:51, 20 March 2009 (UTC) | | [[russ_hensel]], --[[User:DavidCary|DavidCary]] 12:51, 20 March 2009 (UTC) |
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| − | [[Category:Community]]
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