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1831  Using Arduino / Programming Questions / Re: Using arduino to read oilpressure and watertemp sensor, need help. on: August 26, 2012, 04:57:20 pm
Well then a look-up table and extrapolation from point to point... or an equation that describes the non-linearity...

Doc
1832  Using Arduino / General Electronics / Re: LM2917 Frequency to Voltage Converter on: August 26, 2012, 01:31:34 pm
I think (Know) you will find a negative voltage present on pin 1 when the chip gets hot... and there is no path to "bleed" off the positive voltage, Under "No Signal" conditions?.
If you look at the series diode capacitor connection and think about it carefully you will see that at some input condition (pulses in) the cathode of the diode must go positive as the diode prevents the capacitor from discharging and at some point the diode is biased off... it's Basic electronics theory... Electronics 101... try something, measure the current without any input whatsoever (disconnect everything from pin 1) if it is still @ the 60? - 70? mA... If so the device is defective. I've read the attached LM2917 data sheet 3 times and I can't find a schematic even close to your drawing... and pin 1 is the + input to an Op-Amp... The non inverting input to any op-amp is a very high impedance point... There is no discharge path for that 2R2uF cap... which may have damaged the op-amp input...

Doc
1833  Using Arduino / General Electronics / Re: Resistors, many and cheap on: August 26, 2012, 12:08:22 am
I collect books... I have about 30K books... Probably 1/3 duplicates... Am I going to read them all... Yeah, If I live long enough... I'm the same age as you...

Doc
1834  Using Arduino / General Electronics / Re: Splice-free ribbon cable? on: August 25, 2012, 07:24:06 pm
Spliced cable is short pieces that are "spliced" and then put in a special machine to coat or insulate the splice, the difference is that the "spliced" cables are an issue at high bus speeds as the splice is an impedance bump (and physical bump) that can cause trouble. usually much less expensive they are fine for most of our (Arduino users) uses as we don't use long high speed multi-conductor cables.. I used to buy that stuff for low current control cables... it was lots cheaper... By the 1K length... and cut the splices out and put them in the wire scrap barrel... there are likely other reasons as well but that was my concern and remedy...

Doc
1835  Using Arduino / General Electronics / Re: Voltage *and* current regulation for a solar panel ? on: August 25, 2012, 07:14:13 pm
On my first solar powered (SLA charger in order to measure the battery ... I took a measurement of the battery voltage and then I shut down the charger for 5 seconds and made a second measurement... This was done every time I used the device which drew about 100 mA for 100 mS. Doing this provided a charge method that got 3 years use from a Yuasa NP1.2-12 battery as I could tailor the charge to the battery. While I understand the MMPT method... it was done for another reason. The design used (Not my choice) amorphous silicon solar panels. The sputtered silicon type. They as a class have a different life cycle than the preferred crystalline type... they loose efficiency as they are exposed to the sun and can loose as much (the ones I was forced to use) as 30% of their capacity. Today there are solar panels in production that do "wear" out over time. It's easy to tell them apart... they are an amorphous brown color not the pretty blue/purple color of crystalline type... Nor do they look like crystals. This was done before there were efficient one package, inexpensive buck/boost mode switchers that could be processor controlled...

Doc
1836  Using Arduino / General Electronics / Re: Need some help with the concepts of pull-ups/downs. on: August 25, 2012, 06:46:26 pm
Mike it also serves to lower the impedance of the "Termination" so that the "influences" of "Strays" is minimized. If the output is supplying 1 mA (4K7/5V)it takes 1mA + the "stray" to influence or change the voltage at that point... If the current is .5 mA (10K/5V) it takes 1/2mA + the "Stray" to "influence" the measured point... Thus the reason to use as low a value of resistor as is possible... this is commonly done in "Hostile" or EMI rich environments to lower or prevent induced noise from other sources as well as to terminate a line in its correct load impedance. an example is the resistors used to "terminate" an RS485 link, any two resistors that will "Split" the reference (Vcc) voltage can be used... the Bus operates @ Vcc/2... So with ideal components 2 1M resistors could be used... But the bus wouldn't work real well in a noisy or long wire run environment.

Doc
1837  Using Arduino / General Electronics / Re: Wheatstone bridge? on: August 25, 2012, 06:31:17 pm
The Jfet... device is available as a calibrated (measured) diode package from several sources the use of a stable voltage to drive it makes for a VERY stable reference that can supply current to your thermistor voltage divider. You then measure the voltage and apply the correction factor to it and then use it. For an Arduino there is little use for the accuracy attainable with an Wheatstone Bridge as the bridge configuration can easily measure milliohms in 10's of hundreds of ohms... .01 (10 mOhm) ohms/100 ohms = .0001%.. From a an accuracy standpoint you will get more information than you can use. The Principal reason I suggested an accurate reference/divider was to simplify your task. If it is necessary that you learn about Wheatstone, Hay or other forms of the same type of network for your education (Instructors recommended project) there are better ways of dealing with it. However if you must deal with a bridge instead of a simpler divider network then use the lowest temperature and add 10 deg to it and use that Resistance as the beginning point (Make the other resistor in the thermistor side equal to that value and the bridge can never swing negative. It will be a rising potential equal to the difference in value of the two resistors in the "variable" half of the bridge. It in effect becomes a voltage divider again... with two un needed parts whose temperature stability can be a major factor in the total accuracy of the measurement method. I have included a data sheet from one manufacturer of CC diodes. The Jfet idea I mentioned is the beginning of that technology. Basically it is a low pinchoff Jfet and a resistor in series with the source (as I remember...) and the gate is tied to the other end of the resistor when the voltage across the resistor (dropped by the diode load connected to the source, drain to V+) the Jfet cuts off limiting the current to that level.When a precise current is placed across a known value of resistance a precise voltage is developed. I discussed this on line in this thread with another person and there I explained my thoughts... Did you read my response? and my thinking?. A Wheatstone Bridge is a great tool for certain things and a VERY interesting thing to investigate, I've used them for many different things in many different ways... Used one to make an AM modulator for a transmitter I built 30 years ago. I used one to make an FM modulator several years later... these are a few uses I have Bent from the original work I did with bridges when I was in school. In short unless there is some outstanding reason why you NEED to use a bridge remember the total stability/accuracy is dependent on a good reference bias source and 3 other parts besides the measurement variable, a lot of bother for questionable returns. IMO

Doc
1838  Using Arduino / General Electronics / Re: Free (almost) Solder Suckers on: August 25, 2012, 12:46:51 am
Son, I have been using lead based solders for 50 years with no ill effects, I've had my blood checked several times for poisoning for Lead, Mercury and Cadmium among others and has slight levels of lead and mercury... Never toxic and never enough to do more than show up in a mass spectrometer measurement of my blood. Lead isn't nearly as toxic as you might think... for young children it's a REAL Problem a VERY Serious Neurological Issue but for a mature human it isn't much more dangerous than eating fish... (Just don't eat a lot of fish frequently_). I just don't put it or my fingers in my mouth and I wash my hands well after using it. The Dangers are really from landfills more than unit toxicity. The stuff will very slowly become chemically involved usually with a mild acid or a mild base and slowly becomes water soluble where it enters the food-chain and it will cause serious neurological damage to unformed nervous systems... Children both pre and post natal. It isn't as dangerous as it is claimed however it does require respect and some reasonable care in it's handling.. Especially from things like solder suckers as they contain oxides of lead and those are readily soluble, That's why I made the joke about discarding them when full... the dust from that type of device is somewhat more reactive then plain solder. I would be more concerned with the effects of the new family of "Organic" Fluxes... some contain phosphorus and it doesn't take much beyond the right combination of metals and contaminants to make some fairly toxic chemicals... (there are a lot of poisons made from phosphorus) a Fan is a good remedy for that though... or better a soldering hood. BE careful but not fearful of solder... and I HATE that lead free crap, every joint looks to me like a 'cold' solder joint...
IMO...
Edit: 8/26/12 Doc
Doc
1839  Using Arduino / General Electronics / Re: Resistors, many and cheap on: August 25, 2012, 12:21:40 am
Isn't that a pile of resistors... I have 7 bundles of resistors, 13 values in each bundle and 50 resistors per value... 4550 resistors... All 1% Metal Film. I don't even have room to put them anywhere... At All.
On another note... Entirely...
I bought 1734 ic's today... a LOT of EL2157CN's, a 125 Mhz 12V 100 Ma Op-Amp... Anyone remember that power amp Elektor built a while ago... the one that used 64 NE5532's per channel, Very Clean Very Low Noise power Amp... But 100's of chips... Bet I could build a better one with these... I'm going to make an "Op-Amp" board for this forum... Programmable gain, ability to amplify down to DC and do 1/2 Vcc inputs with ground referenced outputs... I included a data sheet for them. I also bought 50 or so 24V to 5V 3W isolated switchers that have a spec'd 18V min voltage and guaranteed to "Start" @ 12V... great for things like meters for power supplies... Most of the older A/D converter/driver ic's ICL7105 or 6??? and all the knockoff's need an isolated supply because the input ground is at 1/2 Vcc... Fries the chip every time you try to "Ground" the input ground.
There are a lot of digital meters sold on Ebay that have that issue... Also very cool for isolated reference sources for A/D stuff, isolated from ground good for 600 mA and really clean and @ 300KHz easy to filter for the most sensitive of applications although ripple @ 300KHz isn't much to worry about... It's too high in frequency to really matter unless it's like a volt or more (100 MV worst case) and a .1uF will fix that nicely.
I also got 15 LAS300 LEM current transformers... 300A but good from dc to 50 Khz @ 1% or better... So 30 to 60 turns of some 16 or 18 Ga solid wire would fill the hole nicely and with a +/- 15V supply would make a highly accurate 10 - 15 A full scale ammeter... lower values are possible if some loss in the coil is acceptable. I bought them because of their accuracy, I've used them before and they were great, accurate stable and easy to use... no temp comp necessary like the transformer types and no minimum load for accurate calibration, these devices also have cal and zero pots open to the world for easy "Adjustment"...

Doc
1840  Using Arduino / General Electronics / Re: Audio AC Coupling Help ! on: August 24, 2012, 11:06:28 pm
If you get the national data sheet for the LM386... there might be several choices as many people second source that ic. The National Semi one has all the reference designs you will ever need... 3 of them as I... included the correct data sheet I looked at it first and it is the one you want. BTW a 22uF coupling cap should work just fine... Always has for me.

Doc
1841  Using Arduino / General Electronics / Re: digital oscope suggestions? <500$? on: August 24, 2012, 10:57:41 pm
Interesting the specs make it a basic audio - low RF scope... @ 12 Mhz vert 3 DB BW and 10 Mhz sweep... The Spectrum analysis would be ok to a MHz The Generator and Bode plotter are interesting too, make a GREAT setup for developing audio filters possibly to a MHz or so. The Sig gen is likely one of those new DDS chips, I own one that is good to 5 MHz and it is nice to be able to rapidly sweep a network and look at it's response. Perhaps a little pricey for a beginner but a great beginning, well equipped and really nice equipment. Great tool for an Amateur Radio enthusiast (WA7EMS) . If I worked lowband radio I would love to have it... Vellman generally makes fairly solid devices, the few I've bought worked exactly as advertised.

Doc
1842  Using Arduino / General Electronics / Re: Need some help with the concepts of pull-ups/downs. on: August 24, 2012, 08:13:39 pm
No on both points it would take 1/2 the "induced" voltage to cause equal interference with a 10 K resistor as it would with a 4IK7 resistor it will source or sink .5mA, a 4K7 will S/S 1 mA and a 470R will S/S 10 mA. The more current (to a point) pulled up or down the better conditioned the port is to outside interference, especially if you connect long (more than 6 - 8 in) wires to the ports in question. A "terminator is any connection to a port pin to determine it's function and If there are either unused pins or long wires connected (Short ones too) to pins used for indication from or to external devices they should be "Terminated" properly connected and pulled up or down depending on pin function. in short pull-ups or downs are terminators...

Doc
1843  Using Arduino / General Electronics / Re: digital oscope suggestions? <500$? on: August 24, 2012, 08:02:05 pm
The whole point of this thread so far has been the monitoring of a pin or two... not the contents of multiple outputs... perhaps shift registers... and the best tool for the job. My point is that both scopes serve different purposed and are in many ways better suited to  a specific task, digital works better for digital and analog works better on analog signals. Looking as t Pure Sine Wave that I am Listening to and seeing "Stuff" that I can't hear but is clearly displayed on a cheap digital scope is somehow wrong... a Digital scope is more valuable for absolute level and time measurements both immediate and through storage.
Neither task is well performed by a Logic Analyser... and you couldn't fix your stereo easily with a logic analyzer But you could use either a digital or an analog scope for that purpose.. IMO

Doc
1844  Using Arduino / General Electronics / Re: Time for a new iron on: August 24, 2012, 07:41:32 pm
It Is... I just use Ebay cause they are more or less in the same place, lazy I guess...

Doc
1845  Using Arduino / General Electronics / Re: Low pass filter -- how hard can it be? on: August 24, 2012, 07:37:34 pm
There is also 'common mode' noise which is just the ground differential voltage.... ground is Not necessarily Ground when it comes to pulses with that rise time... Especially if you have a computer connected to the USB port. Real noise will be diminished by the filter common mode noise will not, It's not flowing through the filter...

Doc
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