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10801  Using Arduino / Motors, Mechanics, and Power / Re: Protecting Arduino connected to a power supply? on: February 17, 2011, 12:40:55 am
Which servos are you using?
Not all hobby servos can handle 12v.  Most of mine let the magic smoke out at that voltage.
Many of the newer ones can handle it though.

Can you give us a link to some of those 'newer ones' that can handle +12vdc?

10802  Using Arduino / Programming Questions / Re: Stopping signal output to servo when input unchanging. on: February 16, 2011, 11:21:01 pm
I talked to Hitec and they said it would greatly reduce the life of the servo but if I turned it off while holding a position it probably would not be detrimental so long as it is not used continuously at that voltage. Having the voltage across the servo doesn't matter though I think. So long as it has no control it is not doing any work and thus not generating any heat.

That's not my take on it at all. As long as you have +10 vdc applied to the servo's power pin you are stressing the heck out of it and I would never recommend running a servo at above it's rated voltage range, most spec 4.8vdc to 6vdc. The fact that the servo is detached with no control signal just means the motor won't be drawing current, but that has nothing to do with voltage stress on all the semiconductors used inside the servo. Running components above their maximum recommended specification is never a good idea. If you need a stronger faster servo then buy or build one. At least that's my advice and worth what you are paying for it.  smiley-wink

10803  Using Arduino / Project Guidance / Re: Spray can and Arduino on: February 16, 2011, 11:12:16 pm
Just buy a mean dog. No legal problem if your dog mauls a burglar if it happens inside your home.

10804  Using Arduino / Project Guidance / Re: Voltage/Current control via PWM? on: February 16, 2011, 11:07:51 pm
I hope this clears things up.  It's difficult to convey an idea without actually spilling the beans.  But I think you can get the point.  Actual values do not matter here in this forum.  I'm mainly looking for methods.

I'm afraid you have given us not enough to work with. A schematic drawing would be a nice starting point, showing the wiring and what and where you want to measure and/or control. You don't have to name the mystery parts, just draw their equivalent electrical properties.

I suspect that if this was such a great secret project that the techinical players could better describe the basic function they are requiring from the arduino. Saying it will sometimes be turned on and other times turned off is probably true of 90% of the Arduino projects ever built.  smiley-wink
10805  Community / Bar Sport / Re: My first and probably last arduino project on: February 16, 2011, 10:53:57 pm
Only then did I notice that there was a 100 megawatt 50 gazillion lumens street light that shined all over that viewing area.

That's funny.

Is now, back then, not so much. I did spend a couple of weeks trying to figure out if I could make the street lamp turn off. Like most street lights it had a sensor so it didn't waste power trying to compete with the sun, so I tried aiming flash lights, spot lights, etc to trick the light sensor, but to no success. This was before affordable lasers so maybe that would have worked? I really really really considered just shooting the damn thing out, but I guess my conscience got the better of that idea. Plus with my luck they would just repair it in record time.

10806  Using Arduino / Programming Questions / Re: Different Tabs on: February 16, 2011, 10:46:53 pm
Lefty, if you write code in a separate .pde file, you need not worry anything as all .pde files are concatenated before compile so it the same as writing all those lines of code in one file, which is not very visually appealing.

If you put anything in .c or .cpp files, those files are compiled separately and later linked together. In order for the main .pde to use any functions (old fashion C or C++), you need declarations of these functions in your main .pde file.

I'm writing a blog post on this issue. It's mostly done but I'm still typing the last part.

I look forward to reading again when completed. Please repost when your done.

10807  Using Arduino / Project Guidance / Re: Measure time for a tank to empty by weight on: February 16, 2011, 10:17:17 pm
@Graynomad I wish I was < 25 smiley

Calculating flow shouldn't be a problem

Get a reading every 5 minutes
Old reading - New reading = flow in 5 minutes
(Full reading - New reading)  / flow X 5 minutes = time remaining

Ah, the old rate of change calculation. That would be pretty simple. They used that in a refinery I worked in, as they already had a accurate level measurement avalible, so creating alarms on changing levels when the tank was not suppose to be opened to anything was easy, and rate of change gave the operators an idea of when they might have to leave to drive to the tank to shut it in after a large product transaction for the tank. A RTC chip would help make it easy, however just tracking via millis() time stamps should work as well.

10808  Community / Bar Sport / Re: My first and probably last arduino project on: February 16, 2011, 10:11:26 pm
Sound like a telescope project I got involved with many decades ago. I read and researched for a couple of years, finally selected a 8" reflector design and got to buying parts and such. Finally got it all working and took it out the first night to my only available southern viewing site in my backyard. Only then did I notice that there was a 100 megawatt 50 gazillion lumens street light that shined all over that viewing area. The scope worked fine, but my eyes were never able to really dilate to full open enough to really utilize the power of the scope. Oh well I did enjoy learning about telescopes and the project was a technical success, in not a practical success. I learned something from that lesson, not sure what it was but I learned something.  smiley-grin

10809  Using Arduino / Sensors / Re: enhancing to .1 mV resolution on: February 16, 2011, 09:59:18 pm
I need to do some A-to-D sampling of a signal that will range from 0 to 50mv.  I have a few of the Gravitech I2C-ADC boards so I can do 12-bit resolution, but it seems like I'll be sampling way down in the extreme lower end of everything, even if I use a 1.1v reference.  I'm wondering if it would be better to amplify my low signal up to a higher level and sample it there, or would amplifying it cause more noise and error?

Yes, for such low level signals it is common to utilize a instrumentation op-amp stage between the sensor and the A/D convertor. Lots of modules and raw instrumentation opamp chip can fill this requirement. Just start googling

10810  Using Arduino / General Electronics / Re: Trying to do load sensing - how? on: February 16, 2011, 09:48:43 pm
Actually that's a very good question, how can one read how much current a motor is drawing while under program control. There are a couple of ways I can think of. The most non-invasive way it to use a hall-effect current sensor. This has a wire carrying motor current routed through the chip but otherwise no direct electrical connection to it, and output a DC measurement voltage proportional to the current. Advantages are no power loss consumed across a series resistance. Disadvantage might be cost of module, as I haven't seriously looked into their prices, current ranges, and interface voltage requirements. For battery operation on larger applications like robots, etc, efficiency is all important for maximum battery life between recharging.

The more traditional solution is to use a 'shunt' resistor like you have described and just measure the voltage drop across the resistor. It's easiest to interface with a arduino if it's a ground based measurement, so the resistor should be wired from the motor voltage sources negative voltage terminal to the entry for ground of the H-driver chips or low side driver transistors for discrete H-drive designs. As the arduino and H-drive power source should already be sharing a common ground wire, all that is required is to run a wire from the 'hot' side of the shunt resistor to a Arduino analog input pin.

One likes to have as small a resistance as possible as any voltage drop represents power loss to the motor as in watts lost = amps X amps X ohms. However as you stated your .05 ohm resistor will only present .15vdc at expected normal load current and that is a small number for decent resolution measurement on a normal arduino 0-5vdc analog input pin, only reading at 3% of measurement range. However you can enable the internal 1.1vdc A/D reference and your measurement range will shift down to 0-1,1vdc so your .15v current measurement will fill about 14% of the range and that might be usable.

Finally I think some of the H-drive IC modules include current measurement outputs, but I don't recall which ones. As most of these modules have some form of over-current shutdown/protection, they already have an internal means to measure current flow and as I said some give that measurement available on a analog output pin as I recall. I think I recall that anyway.   smiley-grin

Any of that make sense?

10811  Using Arduino / Programming Questions / Re: Different Tabs on: February 16, 2011, 09:29:52 pm
There will be issues with sharing variables between the files, that can be addressed using the extern keyword with the variable declaration in the file that references the variable (not the one that defines it).
How about simple C functions I might write. If I only pass variables in the calling argument list and only use the function return, do I have to do anything special in my main sketch to call the function written in a tab section, called myfunction.c ?

How about global variables in the main sketch, will global variables be avalible in functions written in seperate tabbed files ( and as .c files, and/ or .pde file name type allowed?)


10812  Using Arduino / Sensors / Re: Multiplexing a Thermocouple Input on: February 16, 2011, 04:21:19 pm
BTB, you might want to consider RTDs unless you have some really specific requirement that demands TCs. I've seen them for TC-like prices on eBay (~$5 for a sheathed probe), and they're much easier to MUX in a reasonable fashion. Personally, I find them much easier to use.

As well as much more accurate and less expensive to process on the electronics side.


10813  Development / Suggestions for the Arduino Project / Re: Timestamp option for serial monitor on: February 16, 2011, 04:18:12 pm
Did you have in mind that the serial monitor would keep the time stamp info and post it along with arriving serial messages, or that the arduino would send the time data along with it's serial data?

The former could be a useful configurable option, the later I think most experienced arduino user know how to do already.

10814  Community / Exhibition / Gallery / Re: Car reverse backing obstacle sensor with sonic ranger on: February 16, 2011, 03:50:00 pm
:cheesy grin:

Yea, take a bow. It's a neat example of thinking outside the box. They had an existing sensor(s) and the computing power to spare to come up with a new alarm function without having to add any new hardware.

I was impressed when I first researched it. I was curious because the first time I had to get new tires I inspected the wheels and brake assembly and couldn't see anything I could relate to a tire pressure sensor. A little googling showed that there are two methods. The long haul trucks use a system that does rely on pressure sensors, and is quite expensive option. But it makes sense for them because with 18+ wheels it's not much help to say hey one might be low! The second method was as I explained, just a little freebie sensor based on existing tech already in the car.

10815  Community / Exhibition / Gallery / Re: Car reverse backing obstacle sensor with sonic ranger on: February 16, 2011, 03:40:24 pm
well if it's just the rear(driven) wheels you could spot the differential gear turning
if the car has ABS there could be an output from the speed sensors...

if the car has ABS there could be an output from the speed sensors...

Give the man a cigar. Antilock Braking Systems have a sensor to tell if a wheel is turning or not so as to release brake pressure on a 'lock-up' wheel during a breaking situation. The car just uses this sensor to also determine a rpm for the wheel and does some comparison with the other wheels ABS sensor and reaches a decision if one (or more?) wheels speed differs from the others due to smaller wheel diameter if at lower tire pressure. I'm sure it's not a real sensitive or accurate 'answer' it arrives at, but it is effective enough that after getting such an alarm and stopping and looking at the tires I can't always tell which is the lower one just by eye, I have to measure manual to be sure in most cases.

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