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1  Using Arduino / Installation & Troubleshooting / Re: Killed Arduino by following BlinkingLED tutorial from on: April 28, 2013, 02:59:48 pm
This actually irks me to no end when I see the tutorials with the LEDs and no resistors. There are a few times you can drive an LED without a current limiter, driving from a logic source such as a microcontroller is not one of them.
2  Using Arduino / General Electronics / Re: SMA connector wiring on: April 21, 2013, 05:23:14 pm
You may want to try with both the wire antenna and the external antenna. The wire antenna may perform better unless you board is in a metal box. Coax loss could become an issue at the frequency.
3  Using Arduino / General Electronics / Re: Soldering station not heating up, burned diode? on: April 01, 2013, 08:31:56 pm
Reading room temperature would indicate a faulty heading element. Reading 1 degree C indicates something more sinister and I couldn't help but notice the horrible soldering on that PCB and it looks like it was done by hand with poor quality control and workmanship. A bare minimum you should do is reflow all the joints on the board, it is a failure waiting to happen. Don't worry about D2, it actually looks okay to me, if it were burnt, you would see discoloration on the board.
4  Using Arduino / General Electronics / Re: Undisputed power to the Arduino on: February 20, 2013, 03:19:00 pm
Good quality NiCd cells will work with a C/10 (1/10th capacity) charge current and can handle overcharge well at this point. I'm more concerned with the cutting power off when fully discharged. I would also recommend a higher voltage than 7.2 volts due to the limitations of the Arduino regulator. I recommend at least 7 cells (8.4  volts) so that when the cells near full discharge you still have enough power to have the Arduino cut off power. The over discharge cutoff would be simple. Run B+ through a voltage divider into an analog input. See what 7.2 volts (off of a lab supply shows as an analog value in your input through the divider) and the logic is simple from there. If your analog input is less than 7.2 volts then simply turn a digital output to low. This output would feed a reed relay (assuming you have the current available on the Arduino to have an additional 20ma digital output) which in turn would drive the master relay running on B+ but also interrupts B+. When an overdischarge happens the Arduino would simply shut the power down from the battery. A reset switch across the B+ relay terminals would be used to reset the power circuit when the battery is charged.
5  Using Arduino / General Electronics / Re: Opinions on soldering iron + hot air stations on: December 17, 2012, 03:22:36 pm
My answer to all of this is that it depends on what you are working on and your soldering skill. In fact you may end up with more than one of the tools on this list. Here are a list of tools and how I would recommend them to be used:

-25-30 Watt Pencil Iron -- General Purpose, very limited surface mount
-25-30 Watt Pencil Iron with Ground -- General purpose and static/AC sensitive circuits, very limited surface mount
-45 Watt or more iron -- Terminals, RF Connectors
-Butane Iron -- General purpose (also terminals and RF connectors in some cases), some surface mount
-Soldering Gun -- Terminals on non-sensitive circuits (soldering guns cause spikes when turned off and can sometimes light LEDs with the spikes), RF connectors, wire splices.
-Temperature controlled soldering Iron preferably 45 watts or more with multiple tips and digital controls -- General purpose, Sensitive components, Terminals, RF connectors, wire splices, and surface mount components.

Now you can expand that a bit on each one depending on skill. Some electronics techs may use a standard 45 watt iron for most items and some people can use standard pencil irons to do more advanced surface mount. If you do a lot of surface mount, you may want to apply more flux than what is in the solder if needed to prevent bridging in some cases.
6  Using Arduino / General Electronics / Re: Powering LED array from mains on: October 22, 2012, 06:58:18 pm
There are two problems with this approach. First is safety which is covered, second is longevity. Connecting LEDs to the mains is a very bad idea without any type of regulation. LEDs, especially anything using a blue die (Blue, white, pink, purple, sometimes green) or a UV die like you are using are very sensitive to surges and even to static electricity. When you connect to the mains without regulation (using a transformer or not) every surge is going to be passed through to your LEDs. You are proposing a Mains circuit to a rectifier (hopefully through a fuse and preferably an Isolation transformer if the wiring is exposed) to a resistor and then to the LEDs. This leads to problems.
7  Using Arduino / Motors, Mechanics, and Power / Re: 9v Battery Question on: October 17, 2012, 07:40:26 pm
Your lithium ion battery should help. Even a NiCd would have helped you. You aren't running into a capacity problem, you are running into an internal resistance problem. Even a NiCd battery with its lower capacity should have low enough internal resistance to power your circuit, a lithium ion based one should be even better. I wouldn't pull over 100 mA from an alkaline type anyway and that is pushing it.
8  Using Arduino / General Electronics / Re: LOL - Exploded cap. on: October 13, 2012, 12:20:15 pm
I've had a few electrolytics pop in my time with electronics. First I had a power supply with a shorted pass transistor (linear regulator) and hooked up an old car clock. After trying to get it to work (not thinking of an overvoltage problem) the electrolytic popped. Second incident was with a power inverter. Plugged it in and the cheap capacitor popped immediately. I was lucky that they were enclosed in a device at the time as the first one definitely would have gone flying.
9  Using Arduino / General Electronics / Re: Why arduino can fry? on: October 13, 2012, 12:17:06 pm
A short will either shut the regulator down for the DC input or open the PTC (fuse) for the USB.

Yes, but that happens well after you hit the per-pin limit of 20mA.

It protects the regulator, or the device on the other end of the USB cable, but it won't do all that much to protect an overloaded output pin.


That's why I specifically said "short" and not overload as you would have to overload all of the pins at the same time. Still a bad idea to do. BTW, don't the UNO specs say 40 mA?
10  Using Arduino / General Electronics / Re: connecting 2 powersupplies in parallel on: October 13, 2012, 08:29:53 am
Use a separate supply for the heaters (connect the grounds of the supplies together though). Use transistors on the outputs to operate the heaters. If you aren't using PWM, you can use relays instead if you wish.
11  Using Arduino / General Electronics / Re: Why arduino can fry? on: October 13, 2012, 08:26:28 am
Low (dc) resistance isn't the issue: you can actually short your avr's pins without damaging them.

You've done this?

I guess Atmel doesn't know what they're talking about when they give the current limits, both per-output and per-device, in the datasheet.

The simple fact is, you kill the arduino (actually the ATmega) by trying to draw more current than the chip is designed to handle.


A short will either shut the regulator down for the DC input or open the PTC (fuse) for the USB. An overload could easily destroy the outputs. This is one of the reasons I cringe when I see people recommend that an LED being directly connected instead of through a resistor as an LED (or any other diode) is a short that just opens up below a certain voltage.
12  Using Arduino / Project Guidance / Re: Hooking up Christmas lights to Arduino on: September 26, 2012, 03:21:55 pm
Be carefuly with triacs. If you are driving Incandescent lamps this is fine, but if you are driving ANYTHING else this could cause various malfunctions that may likely result in a FIRE. The easiest way to test the relays may be to upload the blink example and connect your relay drivers one by one to pin 13 and see if the load turns on and off based on L flashing. If this works then you have a problem with your Arduino turning the relays on and off too quickly and the armature isn't making contact or making and breaking so quickly that your lamps have not reached temperature as mentioned above.
13  Using Arduino / General Electronics / Re: Regulator gets hot with 7.4v and 11.1v li-po on: September 23, 2012, 02:56:26 pm
Remember that at a full charge these battery packs will be putting out a higher voltage. The 7.4 volt pack will be running at 8.4 on full charge and around 6.6 when fully discharged and actually not recommended as it will drop below 7. Your 11.1 volt pack will be about 12.6 volts (like a Car battery that has been sitting unloaded) at full charge and 9.9 volts at full discharge. Since the 7.4 volt pack could cause problems with the regulator dropping out and not providing the full 5.0 volts, you should go with the 11.1 volt pack, but you run into the problem of heat on the boards regulator.

The fix for this is to dissipate that heat elsewhere, but how? This again is simple, use two regulators in tandem to disipate part of the heat on board (internal regulator) and some elsewhere (external regulator). All you need to do is build the external regulator circuit (very basic you can find plans online) with a LM7808 regulator. The 7808 will drop the output of the three cell pack to 8 volts which is above the minimum for the Arduino board and the internal regulator will drop it down to 5.0 volts to power the microcontroller. There is very little efficency penalty in doing this, it simply move some of the heat away from the on-board regulator. You will also want to make sure that your power cuts off when the battery voltage drops below 9.9 (ideally 10.0) as going lower will over-discharge your battery and that is around the drop out voltage of the 7808 regulator anyway.
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