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1846  Using Arduino / General Electronics / Re: Choosing capacitor for crystal on: August 24, 2012, 07:21:11 pm
As far as the crystal is concerned, it doesn't make any difference... It is happy either way, the oscillator pins are marked because it is possible to 'clock' the chip from another oscillator... or another processor 'clocked' from this one. Since you aren't doing that the actual pins used for the crystal are unmarked on the crystal and unimportant as to ...

Doc
1847  Using Arduino / General Electronics / Re: Need some help with the concepts of pull-ups/downs. on: August 24, 2012, 07:14:45 pm
If you use those pins it is a good idea to use a lower value of pull up or down resistor 4K7 is a good value it will source or sink 1 mA of current so an accidental pin change isn't going to draw much current.
Nor will the pin be as sensitive to noise and stray electrical fields. That kind of 'accidental' pickup has bitten me several times... thus the low value of resistor. I want to know... that a pin is high or low.
I use 470 ohm resistors for my terminator resistors. If I make an error in a sketch it's only 10 mA 1/4 of the pin 's current source/sink capability and I see it on the amp-meter I use to monitor my projects current drain with.

Doc
1848  Using Arduino / General Electronics / Re: Wheatstone bridge? on: August 24, 2012, 06:23:45 pm
My Comment was based on the fact that a Wheatstone Bridge can swing negative and is equally likely to do so as to swing positive and on top of that... If you are after ~1% accuracy it still requires a Very Clean, Stable and known Reference Bias for the sensor... Then there is the issue of the accuracy of the Vref, nominally 5V or the chip Vcc. This forces a ratiometric measurement because the Vcc line might not be very stable or accurate. There are similar issues with the internal 1.1?V reference... it seems that it can vary somewhat. So I made these assumptions about the use of the thermistor because there are many ways to achieve that level of accuracy but the temperatures are lower, the thermistor can be limited only (reasonably) by the melting point of the solder... Not all or many but possible. So those thoughts first I thought to recommend a voltage source stable enough that it could through the proper voltage divider be the Vref for the measurements as well as the Thermistor Reference bias... that was to come after he gave me some indication that he understood my thoughts and was interested.

Doc
1849  Using Arduino / General Electronics / Re: Free (almost) Solder Suckers on: August 24, 2012, 04:06:58 pm
Buying Three of them... @ $0.51??? Why not? and Free ()for me) shipping too. I covered that reason rather well too I thought...  in a previous post.
When one gets full rather than having to deal with the toxic waste...
Just toss the whole thing and get a clean one...
3 are likely going to be all I will ever need as I am retired and no longer doing production electronics... So I bought 3...{Edit, Was 33} kinda like Christmas... real early.

Doc
1850  Using Arduino / General Electronics / Re: digital oscope suggestions? <500$? on: August 24, 2012, 03:49:35 pm
I SEE and I apologize... My comments were slightly left of center...

Doc
1851  Using Arduino / General Electronics / Re: How much WATTS do I need? on: August 24, 2012, 03:48:01 pm
Use an LM386N, the reference designs work well just find one here and apply it...

Doc
1852  Using Arduino / General Electronics / Re: Wheatstone bridge? on: August 24, 2012, 03:46:42 pm
Well get out your books and reference the devices... a constant current diode is a jfet operated at it's "pinchoff voltage"... they are available in 2 lead diode like packages... a constant voltage power supply feeding the diode will produce a constant set of conditions that the thermistor can react to.
The Wheatstone Bridge is a fine tool but because of it's bi-polar nature is much more difficult to directly interface to the A/D inputs on the Arduino.
Reference the "Star" method of power supply distribution in your texts and see what I was talking about as far as noise both distributed from the power supply and created by individual elements...
Getting back to the thermistor issue, a constant current through the thermistor will produce a variable voltage, temperature dependent and that will give you the information you need from a stable source.
I hope this helps a little. Unfortunately I need to go and do some "Honey Doo's" now and I will be busy for the next 3 or 4 hours... I think.

Doc
1853  Using Arduino / General Electronics / Resistors, many and cheap on: August 24, 2012, 03:25:06 pm
Amazon, Amazing. I bought that 3400 1% Metal Film resistor assortment. I am looking at 7 bundles of 13 values each X 50 resistors all for $29.00 (7bundles X 13values  X 50 pieces = 4550 total resistors from 0 ohms to 10 Mohms... it came in a 10 X 4 X 3" box and weighs almost a pound... It's from Veroboard Too... quite a buy, I think... (free 2nd day shipping too with Prime)...

Doc
1854  Using Arduino / General Electronics / Re: digital oscope suggestions? <500$? on: August 24, 2012, 03:15:58 pm
Most "better analog scopes have both delayed and "other channel" trigger functions that could well have captured your event.
If you set channel B to trigger on the beginning of a sequence then channel A could be triggered from any event from the channel B source.
I do understand your choice and it was a good one based on your equipment available and the required task.
I frequently use delayed triggering from channel B to either enhance (brighten) a trace on channel A or to simply display the event triggered from the derived channel B event... like the system clock for example.
The point I guess is that because I never had the opportunity to use a GOOD Digital scope, I had to learn to use my "poor" analog scope...
The real issue is that "Digital"  is "sexy", most people see digital and a lot of numbers that are SLANTED to make the instrument look good while not displaying the shortcomings of the digital "guts".
The issue really comes back to "What" are you really looking for... faulty code, misused code, faulty design... (typically power supplies and by-passing) or a real issue with a part that isn't performing according to your understanding of the data sheet...
That was my MAJOR area of failure in design... NOT Very Carefully... READING the data sheet... or trying to "Bend" a part to do something not well covered or recommended by the part designer... Mostly I figured out a method to make them work... Because that is "Where the Rubber Meets the Road".
And No one really remembers your successes But NO ONE ever forgets your failures...

Doc
1855  Using Arduino / General Electronics / Re: 2 linear regulators on: August 24, 2012, 02:48:56 pm
Use the switchers if you possible can at all. use two and separate the loads according to function. A linear regulator can be thought of as a "Voltage Variable Resistor"... Heat in a regulator is wasted power... Much better to deliver that Power to the load than to warm the environment... The Environment won't turn your wheels... If you are really paranoid about regulator failure... something that never happened to me in production and use of Both buck and boost mode devices, a simple "crowbar" (SCR and a Zener diode)  device can be used to "Blow" a fuse and I recommend "Polyfuses" in the 12V supply to the switchers...
I used Tranzorbs... 1.5KE18's for the 12V stuff and 1.5KE 6.8's for the 5V stuff as they also provide spike clipping, should it happen... it never did for me But any protection at all is good.
Easy to find power issues... the higher current's drawn by "defects" cause the fuses to get hot...
Use Your 10 "digital wattmeters" or fingers.... to find a "hot" polyfuse
Linear regulators are easy to use but mostly really inappropriate for power control as they convert unwanted voltage... to heat, Wasted heat unless your "robot" is also your "coffee warmer"...

Doc
1856  Using Arduino / General Electronics / Re: digital oscope suggestions? <500$? on: August 24, 2012, 02:21:12 pm
Most of my work was mixed signal from DC to daylight... really low frequency analog FSK type encoding and decoding... Sensors of all types from hand carried soil measurement devices to large Center Pivot control systems single and multiple radio controlled remote valve control from 1" to 36" valves from 27 to 800 MHz RF control...
An analog scope is great for analog signals and a digital scope is BEST for digital stuff. trying to extrapolate an analog signal from the digital "Artifacting" that occurs when a signal is rapidly chopped can be a real issue... is that "noise" an artifact or a harmonic from a frequency multiplier (RF Transmitter Vcc).
I use and used an analog scope for many years for RF development, Audio or low frequency data voice and basic control stuff.
When looking at a square wave signal on a digital scope is that spike on the leading edge of the waveform an artifact or a Power Supply issue???
The chioce is really simple, good digital scopes (Rigol) can be had for less than $500.00 fully loaded. A Good Used analog Tek scope (2235) can be had "Certified, Calibrated and guaranteed for about $150-$200 MAX used and the 2235 is a 100 MHz dual channel scope... I saw 4 or 5 on a quick Ebay scan @ approx $125.00 (AVG) price. The 100 Mhz bandwidth is the 3DB point...
They're as a class good to 150 MHz or more... easily meeting the Rigol analog measurement spec's. Both types of scopes are valuable for the things they do best...
However there is no scope (affordable by most of us) that will do both well... I see Digital "USB" "Scopes"??? with 10 - 20KHz effective vertical bandwidth's for $150 + dollars... Junk for anything but an Arduino and not very good even for that purpose.
A scope is a serious investment. If all you want to do is digital work then BUY Digital... But buy the very BEST you can afford. If your scope and your EXPERIENCE in properly using it is good you have a fine instrument...
But IF you have little experience in digital scopes you can spend a lot of time fixing both Digital AND Analog things that ain't broke....
Perhaps the easiest comparison would be a fine target competition Rifle... is NO BETTER than the man pointing it...
... IMNSHO

Doc
1857  Using Arduino / General Electronics / Re: simple OpAmp question on: August 24, 2012, 03:03:02 am
An LMC622 is a dual pin plugin rail to rail part that will include both the supply and ground rails in it's input circuit, that is you can operate the inputs right to ground or to within millivolts of the positive rail, it can even be used to the positive supply rail without drawing unusual input currents or latchup... I used them for years... Great old part.

Doc
1858  Using Arduino / General Electronics / Re: Time for a new iron on: August 24, 2012, 02:55:36 am
The Tips are GREAT. indistinguishable from the "Hakko" brand new in their little bags. Well worth a 2 week wait for 10 good tip sizes and to save nearly $50.00 (figuring fry's last price @$5.95 Ea)
I have several tips I bought new several years back from Fry's Electronics and these look great, Identical too in every respect. IF you have 220 Vac Mains service I know where You can buy a Hakko 936 for $50.00 New in the Box...
It might be a discontinued item but it is a valuable workhorse... I bought one from Electrodragon http://www.electrodragon.com/?f=2
and here is the Url for the ironhttp://www.electrodragon.com/?product=hakko-936907-soldering-station-esd-safe. I bought one and a $15.00 110 to 220 V transformer... Not Nearly as Ugly as the 888 iron is and still $20.00 cheaper...
My 926 has lasted for nearly 20 years... A GREAT soldering iron, a real good tool investment.
I cried when I paid $279.95+ tax for my Fluke 179 and besides horrendously expensive fuses (22 24 $ per set of 2, 440 mA and 11A fuses) in the long run though it was one of my best tool investments... buy them Right and Buy them once...

Doc
1859  Using Arduino / General Electronics / Re: digital oscope suggestions? <500$? on: August 24, 2012, 02:35:02 am
In all the years I worked for a living I never saw a digital scope that I liked... the digitizing artifacts annoy me somehow. I own a Tektronics 2213 dual trace 60 Mhz BW scope that I used (not the same one) for 10 years at work and except for the sample storage of a good digital scope I don't miss or want one. It was my experience that failures i that required Digital O'scopes could have been better engineered from the start. On the 3 or 4 times I thought I needed and in fact rented and used... A more carful read of the data sheets and some common sense was the fix and the scope was of little use except to verify what I already knew... I'd made a design error or worse forgot a bypass capacitor or placed it too far from the noise source.

Doc
1860  Using Arduino / General Electronics / Re: Tips on double sided PCBs... on: August 24, 2012, 02:17:47 am
Take your time and practice, You Will get better... It's all a process and each step is different requiring a different technology and skill set. I made my first boards by cleaning my own material and literally coating and curing the photo resist in the same environmental chamber the production girls used to heat their lunches. I did my artwork with pen and ink and those Bishop Graphics pads and tape... at 4X scale I had the 'Artwork lithographed at 1 - 1 scale (reduction hides many small sins). I used a photo contact exposure frame to hold the negative to the PCB and the sun to expose the sensitized copper PCB's. I made a bubble etcher from an old Aquarium filter aerator tank and some PVC tubing and silastic silicon caulk to "Glue" gown the bubble tubing and the air pump supplied the air for the bubbles...
I drilled holes in the corners to attach nylon strings to pull the etched boards from the etch tank... total cost in 1967 was about 15 dollars for a bubble etcher that could handle two 8 X 10 boards every 20 minutes. For plate through's I used 30 Ga Kynar wire wrapping wire stripped and placed through the holes prior to insertion of the socket. I would insert and flatten the wires to the board and place a piece of masking tape on the solder side of the board to hold the wires long enough to insert the socket... I had no real issues with my setup and it was the first time I ever had made a PCB in my life...
Days long gone... for the better I think... Very hard to do a DRC on a tape layout or a BOM for that matter...

Doc
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