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1  Using Arduino / Sensors / Re: Measuring real-time displacement of large steel cable in motion on: September 22, 2014, 05:11:41 pm
What is the range of motion? Are we taking millimeters, centimeters, or meters?
2  Using Arduino / Project Guidance / Re: Help. Please Help on: September 22, 2014, 01:24:16 pm
OP needs to read this ^. And the sticky post- " how to use this forum"
3  Using Arduino / General Electronics / Re: External VI and USB-Power on: September 22, 2014, 05:00:09 am
The auto source select circuit works with a comparator opamp which basically looks at Vin and 3v3. When Vin goes a set amount higher than 3v3, the opamp' s output switches off the p channel FET; effectively disconnecting vusb and the unit is powered off Vin through voltage regulator. At least, I think that's how it works...
4  Using Arduino / Motors, Mechanics, and Power / Re: Problem with MG996R on: September 21, 2014, 03:29:57 am
^yes. Sounds like you are power cycling the arduino, because the servo draws too much current. At startup and stall, the mg996r can draw  more than 2 amps.
5  Using Arduino / General Electronics / Re: Switching Power Supply Plans? on: September 21, 2014, 03:17:31 am
An SMPS is no trivial thing to design from scratch. I would strongly discourage attempting it. An "offline switching power supply" is more doable, but you are limited to only a couple watts in output at best which could be sufficient for a low power arduino project. The best alternative is to use a usb wall charger. Crack it open, pull the guts out and incorporate it unto your project. Ebay also has 1, 2, or 3 amp smps in the $3-$10 range.
6  Using Arduino / Motors, Mechanics, and Power / Re: Switching ac. 120v, 240v,460v, single and 3 phase. on: September 12, 2014, 04:31:26 pm
The probe will output a very small analog signal in the milli volt range. This signal will need to be amplified; there are plenty shields and example code available. I have used stamps by Atlas  Scientific. We will need more info about the motor type to help with a solution for the output side. It could be as easy as solid state relay or it could require a much more expensive drive.
7  Using Arduino / General Electronics / Re: Controlling high power transistors with arduino on: September 05, 2014, 12:09:36 am
20ma is usually consider the comfortable upper limit. Most modern BJTs have a beta of at least 100. But one in the 3-5 amp range is a little less common. A darlington pair or better yet a MOSFET h-bridge would be more applicable. If the l293 is an acceptable temperature when running, the heatsink must be sufficient. If it ain't broke don't fix it. And it's a relatively inexpensive chip. But if it runs hot to the touch, best to find a substitute.
8  Using Arduino / Motors, Mechanics, and Power / Re: How Many amps does this transformer output? on: August 23, 2014, 12:29:43 am
Also don't forget base resistor between the arduino and transistor. Otherwise you risk damaging the arduino pin.
9  Using Arduino / Motors, Mechanics, and Power / Re: How Many amps does this transformer output? on: August 23, 2014, 12:21:00 am
Those " arduino motor drivers" are typically very inefficient and require considerable heat sinking in order to get close to their rated output. Do you have  info or datasheet on your driver?
10  Using Arduino / Motors, Mechanics, and Power / Re: How Many amps does this transformer output? on: August 22, 2014, 01:11:54 pm
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, the power from the controller blew through them and they did not work 
what does this mean? Did the transistor blow up? How was it connected? A Schematic and or picture would help. Which transistor? 1 amp is cutting it a little close. DC motors have high start up current. Are you using a heatsink?
11  Using Arduino / Motors, Mechanics, and Power / Re: How Many amps does this transformer output? on: August 22, 2014, 11:02:23 am
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Why is listed as VA instead of W ?
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Because transformers work off AC and va is the units for ac power. It is convention... basically. In this situation, it is safe to assume that VA roughly equals watts in rms. Power factor is really only an important consideration in industry and large scale power distribution where efficient power transfer is crucial. i have never needed to calculate power factor for any of the small projects I have built.
12  Using Arduino / Motors, Mechanics, and Power / Re: How Many amps does this transformer output? on: August 21, 2014, 09:36:09 pm
Theory aside...The transistor selection depends on whether you want to control AC or DC currents. AC currents require a triac (BTA136 perhaps) or scr and usually an optocoupler driver (MOC4031) for isolating ac an dc. The common way for controlling dc is to use a logic level mosFET.
13  Using Arduino / Motors, Mechanics, and Power / Re: How Many amps does this transformer output? on: August 21, 2014, 09:04:26 pm
Also the current rating is an indication of how much current you can draw without causing excessive voltage drop or overheating the transformer. You can usually draw more current at the cost of losing voltage. So simply shorting the transformer out with an ammeter is not the best indicator of how much current it  can reasonably produce. You really need to increase the load while monitoring current and voltage because open circuit voltage is significantly higher then short circuit voltage (or rather overcurrent).
14  Using Arduino / Motors, Mechanics, and Power / Re: How Many amps does this transformer output? on: August 21, 2014, 08:48:11 pm
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incandesent lights have filaments, which makes them inductive.
I disagree. Incandescents are practically entirely resistive. Power factor is a negligible consideration for small appliances  under normal operating conditions. However, people have been known to do some illogical things. IF you are using it for its intended purpose, it should be ok. Given the 7.5va rating I would estimate it should be capable of .5 amps. Hard to say though since it's a dual voltage supply and only gives one power rating, so you can only assume it's a combined rating.
15  Using Arduino / General Electronics / Re: Arduino Motor Shield - Voltage Supply on: August 19, 2014, 01:30:44 pm
The mega has an automatic voltage selecting circuit that should only allow it to be powered from one source at a time . I would have to look at the schematic to be sure, but I think the barrel plug takes precedence over usb.
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