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SuicidalSmurf posted:Also, the way I am reading the pinout (#27), will I need to do this resistor tomfoolery to charge the ipod (this is the newest ipod classic 80gig), or is there a better way. After having read USB spec for the last three days, I suspect yes. You're putting voltage on the USB bus lines to make it look like there's a USB bus actually connected. Without those resistors, the ipod won't believe the rest of your "tomfoolery", no matter how correct your voltages are.
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Feb 6, 2008 11:00
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SuicidalSmurf posted:Another electronics 101 question. I need to pick up a theory book. I remember what it is that I want, but how to get it done is a mystery to me. I'm not even sure which type of transistors I want to use, I just want to throw a circuit together and have a work. Understanding how it works would be an added bonus. This is a flip-flop, specifically a "T" flip-flop. You can get them on chips individually or wire them with a small number of gates. A TFF is just a kind of JK flip flop with the inputs connected together. http://www.play-hookey.com/digital/jk_nand_flip-flop.html
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Feb 7, 2008 03:23
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I asked this somewhere else, but I'll ask again here: If you connect an LED whose voltage drop is 1.2V at max current to a 1.2V source, why do you still need a resistor in the circuit?
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Feb 7, 2008 03:26
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mtwieg posted:Ideally it will be fine, but in practice it's a bad idea because the Vf will vary, even between similarly specified leds. If its Vf is 0.1V lower than expected, you may very well be looking at a double in current. And of course the voltage source will likely have its own issues with line and load regulation. I'm asking because it doesn't make sense (to me) to have a resistor when using a single AA battery to light an LED with a max drop of 1.4V. If the battery starts at 1.4V max and only gets lower as it discharges, why put more components in the circuit?
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Feb 7, 2008 11:08
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I got a resistor, trimpot, capacitor, NPN, PNP, and LED assortment. I also got a 555, 556, and dual opamp. I figured I could use the 555 to make lights blink using information found in the datasheet. I'm switching on an NPN to avoid burning out the 555. I model this thing in LTSpice, and the waveform looks good. When I wire it on the breadboard, the LED is always on. What did I do wrong? If I don't hook the 555 to voltage, the LED is NOT on, so I know that's doing something. Oh yeah, I'm using a slightly dead 9v battery to power the thing, that's why V1 is 8.4V. The voltage hasn't drooped at all in the last couple of days, so I guess I'm not drawing that much current. R1 and R2 are 50k pots, everything else is fixed resistance.
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Feb 9, 2008 19:08
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Ok, if I remove the LED/transistor entirely and just read voltage at pin 3, still nothing. I've triple-checked everything. I've even duplicated this circuit on BOTH sides of my 556 to no avail. What gives?
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Feb 10, 2008 03:34
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Ok, I'm back. I'm still dicking with that 555/556 blinky light maker. I've put this circuit on a 555 and both sides of a 556. Identical behaviour in all of them. When I touch the "output" pin to Vcc, the LED latches on. When I touch Vcc to "THRS" it turns off. This doesn't make any sense. It won't turn on when I hit "TRIG" or "CV" just "THRS". Did I burn out a 555 and both timers in the 556? What other faults could exist? How can I check to see if my 555/556 is burned out/dead/whatnot?
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Feb 14, 2008 01:08
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mtwieg posted:Umm you should never touch an output directly to a low impedance (either supply rail). That'll kill the IC quick. Touching thresh to Vcc should make the light should go off, so that's okay. quote:Make sure everything is right. Then probe the capacitor voltage. It should be changing between 1/3Vcc and 2/3Vcc. If it's above 2/3, make sure your discharge pin is attached. If it's below 1/3, make sure the trigger pin is attached. If it falls and rises between 1/3 and 2/3, then it's working. When the light is on, the cap is at rail voltage. When the light is off, it's at 0v. I think these chips are burned out.
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Feb 15, 2008 11:12
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Jabab posted:I would've thought it would be I=0.03A*3 so 1.5/0.09 because there's 3 LEDs. Also there's different types of resistor like 5% 0.25W resistors for example. How do you know what to pick? Nope, connected in series, the same current flows through all components. If 30mA is going through one, it goes through them all. Once you find your resistor's value, you can calculate the power with P=I^2*R. From the above, that's 50ohms, so .03^2*50=.045W, or 45mW; a 1/4W resistor is plenty. Even if they are 30mW LEDs, you can still get a current from them directly I=P/V. .03/1.5=20mA. Using 20mA, that's a 75ohm resistor, coincidentally at 30mW. 1/4W is still fine. babyeatingpsychopath fucked around with this message at 20:59 on Mar 2, 2008 |
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Mar 2, 2008 16:49
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clone posted:A quick question that I thought might be appropriate for this thread. It's probably because the normal charger doesn't suffer from current droop when the LCD changes. Car chargers have notoriously small wire and high-resistance connections which definitely limit current delivered. I bet a medium-sized filter cap in line with the positive supply wire would help a lot. Cleaning out your cigarette lighter and the terminals of the car charger will probably also help.
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Mar 16, 2008 17:51
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jovial_cynic posted:Regarding the v6 source, you guys are speaking a little over my head. All I know is that by looking at this page, it says "Supply Min = 6 Volt; Supply Max = 36 Volt". And when I look at the LM386 cover sheet, it says that the chip has a "Wide Supply voltage range: 4V-12V" And knowing that the LM386 can be powered by a 9v, I assume that the meaning is similar -- any DC power supply between 6v and 36v (like a 9v battery) will work for the KA4558. The thing about opamps is they need dual voltages, because they amplify signals that have both positive and negative voltage. Without positive and negative voltage (or differential voltage, such as from a voltage divider) the opamp just won't work at all. It will "do stuff" but not what you think it should be doing. With DC filter caps on the input and output, it won't do anything at all. I played around in spice with this for a bit and am convinced that opamps are magic.
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Mar 21, 2008 00:11
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I got an LM317 voltage regulator, and it's totally tits. The datasheet for the thing is 26 pages long, six of which are schematics showing you how to do stuff. One of the "stuff" things you can do is have digitally selected output voltages using transistor-controlled resistors. This, I understand. What I don't understand very well is how this device works. Does it need a resistive load on the adjustment output, or will a differential voltage load work? I'd love to be able to infinitely vary my output voltage using a DAC. I'm not sure if a variable resistor that can be controlled electronically even exists. Does a transistor work this way?
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Mar 29, 2008 02:19
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SnoPuppy posted:And you can! The easiest way to think about it is that the regulator wants to keep its Vref at some constant voltage (probably 1.25, if I am remembering correctly). It will adjust the output until this is stable, hence why you need the feedback resistor and then the resistor to ground. If you didn't have the feedback, it would just hit one of the rails. This is so awesome; thank you so much.
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Mar 30, 2008 16:16
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My electronics prototyping area was getting quite cluttered so I went down to Radio Shack and bought their Electronics Learning Lab thingy. It's a solderless breadboard surrounded by LEDs, pots, speakers, that kind of thing. Keeps the LED Driver circuit off the end of my breadboard, the speaker doesn't fall off the back of the desk, and the power supply is hidden. Well, the thing was designed to run on six AA batteries and take a tap of each to get multiple voltage sources. There are headers for 1.5, 3, 4.5, 6, 7.5, and 9 volts. I wired up a linear regulator to an old wall-wart to get a nice, clean 9V out, then used a bunch of 10k resistors as a voltage divider. I matched my resistors pretty well, so I managed to get 1.49, 3.00, 4.48, 5.98, 7.3, 9.0V on the headers. Close enough. I don't really like the voltage divider idea, though. I'd like to build some kind of power supply that gives +1.5, +3, +5, +9, +15, and -15V, all reasonably well-regulated and independent, and fit in a space meant for 6 AA batteries. What kind of supplies am I looking at?
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Apr 14, 2008 14:04
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Jonny 290 posted:Instead of using the resistor network to cut down the regulated DC, learn how to use resistors to make a regulator work at any voltage. Presto, variable DC supply. Now, the regulator will give off X watts of heat, where X = (voltage difference between in and out pin) * (current passing through), so you don't want to regulate 15 volts down to 3 and then draw 2 amps of current..... I already have a trimpot in to adjust the regulator to 9.00V. I know how to get any SINGLE voltage; I want to have many voltages at the same time. I can't see pulling more than 400mA at any time on this, with 30-90mA draws being common, so I don't need a huge power supply. I think I can make an opamp circuit that gives +/- 15V. Would it be any kind of good idea just to get some zener diodes for my ranges and throw those in? If so, would I need any other components?
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Apr 14, 2008 20:28
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The PWM circuit is completely awesome. Would it be suitable to make an LED flash based on battery level? Say you have a battery-powered device with a power LED. Once the battery starts dying, the LED starts flashing, flashing more quickly/slowly as the battery gets closer to not being useful? Could you think of another circuit that would be better suited?
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Apr 16, 2008 17:24
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TwystNeko posted:So I just saw this really cool Instructable about Charlieplexing LEDs. I like it. It's elegant, reasonably simple, and trades hardware simplicity for software complexity. Basically, you set up a big bidirectional array and set only the pair you want to "output" mode, then one pin high and one low so your controller is both sourcing and sinking the LED current with all other current paths seeing two or more LEDs and/or hi-Z pins.
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Apr 22, 2008 20:03
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Zuph posted:I have a question regarding servo motors. Think of a servomotor as a device where position is encoded by a PWM signal. If you output a signal with pulse width X, the motor will attempt to drive itself to X. Common servos have 90 degrees of output with 0deg having a 1ms pulse width and 90deg having a 2ms pulse width, linearly interpolated, with one pulse every 20.0ms. If you output 1ms pulses every 20ms, the servo stays at 0. If you start outputting 2ms pulses, it moves until its arm is at 90. 1.5ms pulses have the arm at 45. As I understand it, the 20.0ms should be pretty precise, and the more precise your widths are, the more precisely you can control your arm, to a point. You should be able to get it from there.
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Apr 25, 2008 02:36
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Zuph posted:I can drive the segments fine from the Micro (or, in this case, a shift register to minimize port lines), but each segment is common cathode, so I could (theoretically) need to sink up to 300mA of current. I did a search on digikey for LED Driver, 16-channel, 100mA per channel, and found a couple of decent candidates looking like "IC LED SINK DRVR 16BIT". The data sheet shows a serial data in/out, output enable, failure sensing, thermal shutdown, and 16 outputs in a 24-pin package. $2.94 each. Is this the kind of thing you're looking for?
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Apr 28, 2008 21:59
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zeverken posted:I wonder if any of you electronics wizards can help me with something... I need to tape some telephone conversations on tape for my masters thesis. Is there any way to build a RJ11 (telephone plug) to audio jack converter? So i can talk on the phone as usual, but having everything also recorded on an audio tape? Believe it or not, I just built a box that does this (in addition to some other things). An RJ11 jack has 4 pins. Connect a 500ohm resistor to pin 3, then to the tip on a 1/4" audio jack/plug. Connect the ring of the jack/plug to pin 2. Make sure you don't have the thing plugged in when the phone rings, because there's 100-300VAC on the line when that happens, and it may burn out your recording device. I have some mono plugs from radio shack whose shell is big enough you could probably mount the resistor inside there. I think they're $2 for 2.
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Apr 29, 2008 10:21
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mtwieg posted:Standard component values are based on a logarithmic scale. This is brilliant. Thank you so much. I'm building a circuit to inject tones into audio. Right now, I'm using a 3-bit resistor-based DAC using 3 pins of a microcontroller to make stepped sine waves then filtering with a cheapo RC filter. I can get up to about 10kHz tones, and that's fine for what I'm doing, but is there a better way to do this type of thing? Should I be trying to use a 555 or op-amp oscillator?
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May 2, 2008 21:08
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Three-Phase posted:Now this is what I want to do - program PIC chips on my computer. I have a 232 port and a USB port. I liked Microchip's IDE, and the PicKit 2 prototype board. I need something like this, without needing that shitpuck programmer. I have a PICkit2 programmer and "PICkit 2 Low Pin Count Demo" demo board that work flawlessly. I even downgraded to version 1 firmware and ran it on linux flawlessly for a bit, just to make sure I could. I then upgraded the firmware back to v2 and have been running with no problems ever since. I only have a 16F690, but I've got a tube of 12F675s and 16F688s coming. I'll have my first ICSP-based project up and running in a couple of days, hopefully, and can report on how well that works, too.
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May 12, 2008 21:29
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Zaxxon posted:Can someone help me find some components to order. I need to get some connecters of a specific type. I think your "connector you press onto the end of a piece of ribbon cable" is a standard .1" header block, and you can get them in sizes from 1x1 to 60x2. My local electronics store has a whole rack of them. As for a connector you could plug into a DIP socket, you could take another DIP socket and solder a ribbon cable (or whatever) to the socket ends, or just stick them in there, and then plug your socket into another socket.
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May 14, 2008 10:06
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Zaxxon posted:That will work but it's not what I'm thinking of. Ahh. Look for IDC Female connectors in .10" pitch. It looks like you can find "the other kind" [url= here. That site also has the IDC female connectors, so you're in luck. Edit: didn't hit reply soon enough after finding the link, apparently. Good luck.
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May 15, 2008 02:41
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Battle Bott posted:Is this even vaguely a good idea? Can I do the electronics for it for under $100? I think trimpots at the axes of the joints will work for your first draft, but for a full hand you'd probably want some linear potentiometers above the joint so you can get your fingers closer together. A handful of trimpots/linear potentiometers and a multichannel ADC that speaks USB should run you way less than $100.
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May 27, 2008 20:15
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Cuw posted:http://www.sparkfun.com/commerce/product_info.php?products_id=681 found some LED matrixs for anyone that cares. They are 8x8 and the company that sells these even makes a serial backpack so you can just send it a big array and it will decode it and stuff, although they are $50 a pop. Hopefully, your clock speed is sufficient to keep the duty cycle up high enough that your LEDs are bright.
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Jun 25, 2008 18:41
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dyne posted:I'm looking for a little bit of guidance Nothing that complicated. A comparator and appropriate biasing resistors can do it fine. I immediately thought of a balanced bridge, but I'm not sure why.
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Jul 8, 2008 02:54
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Hillridge posted:I code in straight up binary. I have a motorola 68k dev board that i was using until my PIC showed up. i didn't know you could type in assembler and have it run so i was writing in bytecode. Got a cylon face display and a KITT-style fading thingy going before I found out about typing in assembly. So, something besides MCUs is cool with me. I really dig transistors. I think MOSFETs are cool.
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Sep 12, 2008 04:18
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I did some stuff with PICs and electret mics. I sensed when the mic was transmitting by setting the comparator reference to the voltage supply pin and just sampling the output before the cap. The A/D has some pretty big (for a microcontroller) caps so if the voltage was above a certain level, I just assumed the mic was on. Fiddling with the A/D level to trigger at adjusted sensitivity well enough to turn an LED on.
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Oct 31, 2008 04:01
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RivensBitch posted:Which PIC were you using in this scenario? I have a 16F628A which has a comparator but no ADC. I've never used the comparator so I'm going to have to read up on it in the manual. Are you saying I'd just connect +5V to one pin, and then connect the mic to another? Then in software read the pin? I'd probably need a variable resistor between the mic and the pic to set the sensitivity, no? I was using a 12F675. I suspect you could connect a diode to the output of the mic before the output cap and use that to halfwave rectify the output, using that to charge the output cap, then sample your comparator from the output cap.
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Nov 1, 2008 21:19
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I have a sensor that outputs high in idle and a low pulse train when detecting a signal. I want to turn a motor on with this pulse train. Can I do this with a single N-channel FET, or do I need some more signal conditioning? I've got resistors, capacitors, and some NPN and PNP transistors readily available. Ideally, I'd have the sensor's output connected directly to the gate of the FET and the motor would run, but I'm not sure it's going to work that way.
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Nov 16, 2008 00:14
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mtwieg posted:"pulse train" can mean a lot of thing. Is it variable frequency? Duty cycle? Pulse width? I'm not really sure of the duty cycle or frequency; I think it's about 30kHz or so with >50% duty cycle (more activated [off] than not when sensing) which should work fine for running a DC motor. I can filter it with a capacitor to smooth that out if need be, etc. I'd just like to use a (very) small number of components to trigger the FET to "mostly providing current to the motor" when this thing is pumping out. Congruently, I'd like the motor NOT to run when it's NOT outputting low signal.
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Nov 16, 2008 05:30
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mtwieg posted:What is the logic level of the output, and what voltage is the motor driven at? Would driving it with with a P-channel fet be okay? How much current? And again, do you want the motor to turn on fully when any signal is present, or do you want its strength to have a more linear relationship to the signal? Logic level low for output. Current is pretty low; probably 500mA max at 3V (1.5V motor overdriven). P-channel is fine. Fully on with any signal is fine; I'm regulating the speed with another circuit downstream of this one. A datasheet for the sensor WOULD be great, but such is not available. I'm really trying to avoid buying more components, so if I have to build a latch with PNP transistors, I'll do it.
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Nov 18, 2008 13:24
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Another way to do a VU thingy is to use a clock source, counter, an R/2R A/D tree, one comparator, and a latch. You have your clock feeding the counter, which outputs to your D/A converter (usually an R/2R tree) which feeds your comparator. The other input of your comparator is your input signal. When the comparator turns on, you latch your counter value into your LEDs. It's not really cost-effective for a small number of LEDs, but for 15 or 20, you're looking at a good cost savings. The R/2R A/D chain also means you only have to buy two values of precision resistor. Say you want 16 values. That's 8 dual opamps and 16 different precision resistors. Or 4 ICs (latch, counter, opamp, clock [555]), and 16 resistors of one value and 19 of twice that value.
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Dec 6, 2008 05:31
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I found this tiny buzzer. It's piezo, which needs a driver, but I think a single-transistor oscillator should work fine. Now there just needs a voltage source. It's rated "10Vp-p" with an operating range "1~30Vp-p" @ 5mA max. Is it feasable to drive the oscillator that drives the piezo element with a voltage multiplier? Using tiny SMD caps and diodes on a chip of PCB, I bet you could make one pretty small. In fact, SMD on all of this stuff with a double-layer PCB could be made very small.
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Dec 12, 2008 19:49
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Solaron posted:I believe it's too large around, am I reading that correct? 10mm? Length is no issue, but diameter is, sadly. Ok, I found this one 6.5mm x 3.5mm. I can't find any suppliers, though. Then there's this from digikey. 6.6mm dia. x 3.5mm. These are magnetic; 80mA @ 1.5VDC, and I think you still need some kind of oscillator to drive them.
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Dec 13, 2008 06:18
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The electrical supply house has those buttons, too. I know because we had to get 8-10 of them for the current job. Red 2.5" Round Mushroom-head Momentary Contact switches labelled "emergency stop." They're stocked parts. Same way with Red Guard SPDT Toggle. You can also get wierd toggles there, with or without guards. Single and double-pole, double- or triple-throw (up momentary, on, of; think ignition switch, but a toggle). They even have a really cool section for "stackable" switches, where you have one "operator" rod, and stack contacts behind it. So you have a keyed (or flange, or mushroom or whatever) switch on top, then NO/NC, NO, NC, etc modules that all click together behind it for multiple throws and poles. I think the ones I saw were made by Cooper Wiring Devices and were only a couple of bucks per module.
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Dec 30, 2008 13:29
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Cyril Sneer posted:It's technically possible, but not likely to be practical - moreover, designing a solution would require more information on how the detector works (frequency and power, roughly, would be nice). I think a bulk tape eraser (reasonably large AC electromagnet) sitting on the coil would work fine. Probably a 5lb lump of soft iron with a few hundred turns of wire on it and a few amps DC at 12V would induce more of a field than a bicycle would. Try a few different orientations. Really depends on how far away the thing is. I see that it's 4' from the edge of the road, plus width of sidewalk, so like 8' away, probably. I think this is a great project to just start making stuff and seeing if anything works, and from how far.
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Jan 5, 2009 06:05
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Vinlaen posted:Can somebody please help me understand voltage? I understand the idea of amperage (eg. amount of electrons passing a specific point over a given amount of time) and I understand resistance but I just can't understand voltage. The water analogy is very useful. Think of electricity as water. Current is flow rate. Resistance is resistance. Voltage is pressure. Pressure can only be measured in relation to something else, just like voltage. A battery is like a pump. When it's not connected to anything, the "pressure" between its terminals is some value. When it's pumping water through a closed loop, the pressure measured between the input and output is the same value, ideally. Same way with voltage. A battery has some voltage between its terminals. When it's providing current in a circuit, the voltage between its terminals is roughly the same value. If no current is flowing, the electrons at the battery's - terminal still want to get to the + terminal. Therefore, electrical pressure exists to any points connected to those terminals, thus, there's voltage between them. I feel it important to point out that voltage is a measure of electrical potential at one point relative to another point. The flu is addling my brain, so I can't think of any good examples, but someone else can.
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Jan 9, 2009 21:22
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amotea posted:I'm looking for some sort of robot that can walk/drive around the house, has some type of sensors connected to it, is programmable in C/C++ (or even runs Linux) and is extensible e.g. by adding new types of sensors/actuators. For a 2nd year computer science project we actually had to program such a robot and write device drivers for it (it ran Linux), so I should know what I'm doing software wise, but I have no clue about putting one together myself. iRobot Create. Roomba without the vacuum.
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Jan 16, 2009 04:10
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