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 121 Using Arduino / General Electronics / Re: measuring battery voltage on: December 14, 2012, 08:31:20 am Quote from: Chagrin on December 14, 2012, 12:16:53 amAs lefty just said, the impedance must be 10K or less. That means the first resistor must be 10K or less.Are you sure about that? Perhaps it's because I come from a communications background, but I was taught to treat a voltage divider's impedance as if it was an L-pad. On the source side, the impedance is the series combination of the resistors: 20K+10K=30K, because both resistors are in series with the source.On the load side, treat them as a parallel combination: (20K*10K)/(20K+10K) = 6.66...K, because one resistor is in parallel with the load, as is the other resistor and the source.
 122 Using Arduino / General Electronics / Re: measuring battery voltage on: December 13, 2012, 11:01:45 pm Quote from: retrolefty on December 13, 2012, 08:35:17 pmBut the Arduino analog input pins really wants to see a source impedance of 10k ohms or less for best results. I was unaware of that. If so, then using 20K and 10K resistors (or even 10K and 4K7) would be a better choice.
 123 Using Arduino / General Electronics / Re: Where can I find an insertion tool? on: December 13, 2012, 04:18:49 pm If straightening pins by hand isn't your thing, there are pin straightening tools available. Google "IC Pin Straightener". They're fairly cheap.Usually I just place the chip on its side against a table and bend the pins square, then repeat for the other side.
 124 Using Arduino / General Electronics / Re: connection problem between the wire and the circuit on: December 13, 2012, 04:07:33 pm The sensor circuit is wired to generate a current that varies with temperature. That current passes through R3 and causes a voltage to be developed at Vout.The ground connection is attached to the shield of the cable to eliminate induced noise along the cable path.
 125 Using Arduino / General Electronics / Re: measuring battery voltage on: December 13, 2012, 04:00:56 pm What he said.You can select other divide ratios by taking the smaller resistor and dividing it by the sum of both resistors. For the above example, 100K / 300K = 0.333... or 1/3.  Another example: Using a 56K and a 39K, you get 39/(39+56) = 39/95 = 0.41.     So 12V * 0.41 = 4.92VSubstitute your desired maximum voltages and select resistors accordingly.
 126 Community / Bar Sport / Re: Nutter or Genius? on: December 11, 2012, 10:11:20 pm Actually, when you look at it objectively, the currently accepted value of Pi is the wrong value to use anyway. It's value should be doubled, which makes many equations simpler. Just look at how often you have formulas that contain the constant value "2pi". Pi seldom stands alone.Suggested reading:http://www.math.utah.edu/%7Epalais/pi.pdf
 127 Using Arduino / Microcontrollers / Re: Please educate me on Attiny programmming on: December 09, 2012, 10:43:54 am Why not look here and see:http://www.atmel.com/tools/avrispmkii.aspx?tab=devices
 128 Using Arduino / General Electronics / Re: GE Vacuum Tubes 1950's Era on: December 07, 2012, 05:01:52 pm High voltage is NOT a requirement of tubes.  Pencil tubes, for example, were often designed to operate at maximum plate voltages as low as 12 volts.
 129 Using Arduino / General Electronics / Re: GE Vacuum Tubes 1950's Era on: December 07, 2012, 01:43:01 pm The tubes are possibly ballast tubes, sort of a resistive element that regulates current. They were commonly used to stabilize tuned circuits so that varying voltages would not affect the tuning. Although I have no reference listing the MX-155-5, I base this on the "MX" prefix, which was used for some ballast tubes (MX-408 comes to mind).50's? Ha! I doubt that anything on that board is older than 1970. I know Sperry was still making products under the Univac name as late as 1978, possibly later.
 130 Community / Bar Sport / Re: I hate RF ! on: December 04, 2012, 09:34:13 am You could just let the center stick out (I'm assuming 1/4 wave) or you could fold the braid back over the outer insulation, forming a dipole, then use heat-shrink to cover the exposed braid.Just a suggestion.
 131 Using Arduino / Programming Questions / Re: TelnetClient example on: December 03, 2012, 10:30:29 am Quote from: PaulS on December 03, 2012, 08:45:11 amNo one runs a public telnet server that you can connect to.Not true. They're still around if you know where to lookTelnet.org lists a few.
 132 Using Arduino / General Electronics / Re: Help Finding LED Diffusion Cap on: November 30, 2012, 01:12:43 pm It's probably a custom part, made specifically for that device.Or it's old enough that no one makes the diffusors anymore.Did the original use LEDs or lamps? From the apparent age of the original, I'm guessing lamps.
 133 Using Arduino / General Electronics / Re: DIP Solder header still in use? on: November 21, 2012, 04:31:57 pm That's the trouble with online stuff; you never know if it's been posted for a week, a month, a year...Hope you find what you're looking for.
 134 Using Arduino / General Electronics / Re: troubles with slide pots on: November 20, 2012, 02:20:45 pm Slide pots are notorious for being noisy and intermittent. Dirt and dust fall into them and get ground into the resistive element by the wiper.Also, I believe the 10KDX2 series is a logarithmic pot, which is typically used to set audio levels. It may not be what you want for input to a computer A/D converter. (I'm assuming that's what you're doing.)
 135 Using Arduino / General Electronics / Re: DIP Solder header still in use? on: November 17, 2012, 10:09:55 pm They were actually very useful in their time, which was when wire-wrap was in common use, for both prototypes and production equipment. I've also worked with equipment that used them as programming jumpers, phase-locked loop filters and timing components. (In sizes from 8 pin to 40 pin DIPs)The ones with covers were often used in production equipment. Where I worked, after we got the correct values soldered in and tested, we'd fill the cover with potting compound to seal them and attach them to the header. That kept the customer from tampering with them and altering calibration. But I know that some companies just glued the covers on.The best headers were made of fiberglass or phenolic, they handled the heat of soldering better and were much more durable. The plastic ones were a bit of a pain, easily overheated and damaged. The trick was to keep the pins cool and held rigidly in place while soldering. A socket was the easiest way; I used to have an un-etched square of double-sided circuit board with several sockets soldered to it for heat dissipation. Another method was to find a thick strip of metal 0.3 inches wide, place it between the pins and clamp the whole thing in a small vise to dissipate the heat. I haven't used any of them in probably 10 years, haven't even seen any for sale anywhere.I once had a job to maintain about a hundred devices which each contained  between one and four 4x4" wirewrap boards just crammed full of 7400 logic and headers. The people who built them weren't very conscientious about assembling them and bad wraps, cold solder joints  and occasional wiring errors made them a challenge to troubleshoot and repair.I don't miss that part of my career.Edit: These seem pretty cheap and they look like the good ones I bought years ago.http://eolsurplus.com/Components.htmlsearch for component carrier.
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