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571  Using Arduino / General Electronics / Re: technique for neat smd components? on: February 24, 2012, 09:29:35 am
Correct, hot air systems are great for replacing components or working small sections at a time. But if you have any interest in getting things done quickly, the stencil approach is hard to beat. Plus, there is usually little to no rework after the fact because the solder paste amount is always right (ie no bridges to be removed). I guess it comes down to how much you value your time.
572  Using Arduino / General Electronics / Re: ADC aquisition hipotesis? on: February 24, 2012, 09:03:02 am
Check out the the section at openenergymonitor.org that describes their hardware setup. Their approach uses a Biasing circuit that results in a positive-only signal for the unipolar ADC in the atmega chip.

There is a similar circuit that I explored in this forum that used a coupling capacitor to remove any dc signal components from the AC signal and then biased it sufficiently to remain positive.
573  Using Arduino / General Electronics / Re: technique for neat smd components? on: February 22, 2012, 07:43:21 pm
I order stencils from pololu. I find the prices quite attractive. A $40 toaster oven from amazon does the rest. Techni-tool and other places offer solder-paste with and without lead. My understanding is that leaded paste is more forgiving but the fumes may or may not be bad for you.

I simply pre-heat the oven, then put the board in on high heat (toaster setting) with the board suspended in the middle of the oven cavity. When the solder paste turns shiny and liquifies, I turn off the heat, wait a bit, then pull the oven door open and allow the board to cool down. Has worked great and the stencils are a lot faster than tack-soldering.

Another issue with tack soldering small SMD components is the conductivity of the part - you may need to be really quick to prevent the heat transfer through the part from softening the solder connection on the other end of the component. I tried, and I gave up - 0805 - sized components were simply too much of a challenge for me. I suppose if I had a narrower tip and thinner solder, it might have worked better but with some of the solder landings underneath the components, solder paste is the way to go IMO.

Last but not least, another way to use solder paste minus a toaster oven or skillet on a  hot plate is to use the paste (you can even apply it without a stencil by using a fine tip and a plunger) and then a hot air gun to melt and solidify the solder paste.
574  Topics / Product Design / Re: PCB make+assemble service on: February 18, 2012, 08:55:11 am
I agree. The selection and organization at the typical radio schack has decreased to the point where they might as well not carry anything at all. You can look through the various drawers and find components sorted willy-nilly all over the place.

You are typically better off going to local mom-and-pop stores that cater to the electronic hobbyists. Stores like you-do-it electronics in Boston. I blame several factors: Most kids these days are getting bigger gratification out of blowing their friends up on a video game, lack of electronics education in school, and margin pressures in stores. No matter how overpriced electronics are at Radio Schack, they likely are not covering their carrying costs.
575  Using Arduino / Project Guidance / Re: Non contact flow sensor for heavy oil ideas please!! on: February 15, 2012, 09:03:24 am
There are some heat-based flow detectors on Omega.com. Might be worth investigating. That said, with a 3" pipe, you may have some serious flow variation based on the viscosity of the fluid and the speed at which it is traveling. Friction at the pipe inner surface will slow the flow down significantly from that at the center of the pipe. You will have fun calibrating all that.

If it was me, I'd check and see if there wasn't another way to do it, i.e. put a speed sensor on the pump motor, etc.
576  Using Arduino / Sensors / Re: Diesel Engine Activity Sensor on: February 14, 2012, 02:29:31 pm
Just to re-iterate: The Hall effect sensor would not be used for current sensing inside the alternator. I apologize for any misunderstanding.

To use the electrical circuits inside the alternator as a frequency source, you'd have to measure the rise and fall of voltages post alternator but pre-diode. Most likely with a voltage divider network. But given the voltages and currents involved, I would use this as a last resort. Even then, I'd go with an opto-isolator and similar equipment to keep the stuff in contact with the on-board power supply well-isolated from the arduino. As I recall, there can be some really nasty transients on the alternator as the regulator switches it on and off and/or the engine stops/starts. Never mind the ampacity issues. Like I said, this approach is a last resort, IMO. Stay away from inside the alternator, if you can.

Your hall-effect approach on a moving/rotating part of the engine sounds much more robust and isolates the Arduino from undue voltage potentials. Find a suitable spot with easy access to a mounting bracket, and you're done. I like this approach much better, just as the optical one I mentioned earlier, which may even work in outdoor conditions.
577  Topics / Science and Measurement / Re: Current monitor on: February 14, 2012, 11:57:21 am
It would help to have a diagram of what you are measuring and where in the circuit. The picture is certainly nice to have, but the circuit is more important. Please include voltages being applied, resistances, etc.
578  Using Arduino / Sensors / Re: Diesel Engine Activity Sensor on: February 14, 2012, 09:45:29 am
Hi there,

The hall effect sensor may not require a magnet as long as it's placed near a rotating metal piece that is notched in some way (gear teeth, holes in plates, etc.) If it's sensitive enough and mounted close by, it'll note those changes. Another approach with holes is using an LED and LED receiver.

As for the alternator, I'd consider using a simple voltage detector network with an input into the ADC. Another approach could be the use of a Schmitt trigger / comparator approach where a pulse is sent to the Arduino every time the raw (i.e. pre-rectifier) output of the alternator exceeds a certain threshold. Since you're interfacing with potentially huge potentials and currents, going the alternator approach is less desirable in my view. I'd really look into anything that rotates on the engine that is accessible.

Speaking of which, if a belt is accessible, consider an IR/light approach using the belt. Belts are usually black and engines typically don't enjoy sunlight under operation. Paint a small section of the flat (outside) part with a white stripe and then use an IR sensor to capture the changing color as it whizzes by. Should work. Just be sure to use a color/paint that will not damage the belt. Belts are usually accessible and you may even have a convenient mounting point nearby. I have used a Fairchild QRB1134 IR photoreflector for a similar project, capturing the fastest wheel/indicator on a gas meter in my basement. The application is similar, i.e. a white background with a black dial interrupting the 'view' from time to time.
579  Topics / Science and Measurement / Re: Current monitor on: February 14, 2012, 07:16:47 am
Try using a current sensor instead. Very nice solutions include the S22P series from Tamura. They do most of the heavy lifting for you, i.e. the output signal is always positive, centered around 2.5V so the Arduino can read it no problem. Lesser solutions cost a lot less also, see the openenergymonitor project for guidance, theory, sensor selection, and the arduino code to remove a biasing signal.
580  Using Arduino / Sensors / Re: Diesel Engine Activity Sensor on: February 14, 2012, 07:11:36 am
Why not use a hall effect sensor to measure the RPMS?
Ditto. Usually a water pump, alternator, etc. is exposed enough to mount a sensor nearby. Another option is to hook a sensor wire to the alternator output before it hits the rectifying diodes. Just be sure not to block airflow and to use a very-temp-rated wire. It gets hot in there!
581  Using Arduino / General Electronics / Re: How to coat protect PCB? on: February 14, 2012, 06:58:11 am
The copper on the roof is quite thick, pcb traces are very thin - think 16oz per ft^2 vs. 0.5-2 oz. Some high-quality PCBs feature gold coatings to protect exposed pads but tin-like coatings are standard.

Just as important as the conformal coat though is what to do about leftover flux - it can eat your board contacts slowly over time if you don't remove it or use no-clean flux. I practice lots of scrubbing with 90%+ pure alcohol (nasty on the hands, wear gloves!) though some components also tolerate being washed with water.

Conformal coats can protect the board to some extent - but many parts have to be left uncoated so mask them - i.e. temperature and humidity sensors, connectors, test points that you still need to use, etc. Most heat sinks are at most partially coated so as not to lose performance.

Whether or not you coat, the takeaway is that the coating is but a small barrier. If the board is destined for a nasty environment, ensure that the enclosure can protect the thing. I would also plan in advance re: any uncoated parts that have to be exposed, i.e. make them removable/replaceable using sockets.
582  Using Arduino / Project Guidance / Re: Non contact flow sensor for heavy oil ideas please!! on: February 12, 2012, 01:41:32 pm
A couple of ways come to mind. When I did this for the home boiler, I simply measured the pressure that the fuel pump delivered and then used the Fuel flow chart from the nozzle manufacturer to determine the rate of oil flow. A simple current switch on the fuel pump then allowed fairly accurate open-loop oil consumption measurement.

Can you consider this sort of approach or is your equipment of the modulating kind? Current switches are cheap & noninvasive.

If fuel flow is variable, you can add a pressure sensor on the high side of the fuel pump to determine the pressure and from there extrapolate the fuel consumption.
583  Using Arduino / Microcontrollers / Re: Current Logic Analyzer Choices... on: February 11, 2012, 12:10:27 pm
wasn't meaning to hassle you
only jesting smiley

No worries. Activating the scope for the first time was happy, everything seems to be working. What I need to devise now is a working test.

If there are particular screenshots, etc. you're after, please let me know.
584  Using Arduino / Microcontrollers / Re: Current Logic Analyzer Choices... on: February 11, 2012, 12:09:04 pm
Why use the CD - the up to date software should be downloadable...

Correct, it is. And like most OEMs, they prefer you download it off their web-site. This is especially relevant re: QuantAsylum given that they have all sorts of hardware pins not currently in use that are slated for activation at some point in the future via software.

Today, I'll try to find the time to analyze the waveform generator.
585  Using Arduino / Microcontrollers / Re: Current Logic Analyzer Choices... on: February 09, 2012, 10:27:46 pm
The software installed OK, the scope came up on screen as expected, then I had to rush home to take care of my daughter. Hope to have more news tomorrow.

However, the little I saw was promising.
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