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1  Using Arduino / Microcontrollers / Re: Arduino Pro 8mhz bootloader problem (ATmega328p) on: March 19, 2014, 12:35:50 pm
Never mind, it turned out to be a PEBKAC error. I didn't hook up AVCC properly (the wire was loose so there was no actual voltage on that pin) and for whatever reason, this caused the chip to work on 5v but NOT on 3.3v. I didn't think to check the power and ground connections simply because it worked fine on 5v  smiley-mr-green

Not sure why AVCC (for the analog to digital converter) would be required ONLY for 3.3v operation. I guess only the AVR engineers would know- or maybe not  smiley-mr-green

Somewhat embarrased, but I figured that I can't be the only one who had this problem and I was hoping to "save" someone from this very situation  smiley-mr-green
2  Using Arduino / Microcontrollers / Arduino Pro 8mhz bootloader problem (ATmega328p) on: March 10, 2014, 11:26:18 am
Hey,

I'm having an issue with an ATmega328p. I was planning on using it in a project that runs on 3.3v instead of 5v, so I got an 8 MHZ crystal (with capacitors) and an ATmega328p. I was planning on using the Pro 8mhz bootloader on it. The bootloading process seems to go over without a hitch, at which point I do the "upload using programmer" option to upload my "blink" sketch to the chip. (I changed the blinking LED to pin 9 so that it would not be using the SCK pin)

The blink sketch works just fine running off of the 5v from my Arduino Uno. However, when I disconnect the Uno and attempt to power the chip with a 3.3v regulator, it is totally inert. I've checked the voltages everywhere when the 3.3v regulator is on, and it's not a power problem.  It's not the LED/resistor combination either because if I connect them across 3.3v, the LED lights up.

I thought maybe it was a bug in the bootloader program, like it didn't set the "brownout detect" fuse to the correct value or something like that. I can tell that my external crystal is working and the chip is running off of it, because it only works (on 5v) when said crystal is connected. I've already checked and rechecked the "board" and "programmer" options.
3  Using Arduino / General Electronics / Re: Electrical contact lube? on: November 27, 2013, 05:21:06 pm
I think I'm understanding you. The contacts in question are "logic" switches and thus, do not carry a great deal of current. Thus, the "non-conductive-ness" of the grease probably wouldn't have much effect.
4  Using Arduino / General Electronics / Electrical contact lube? on: November 27, 2013, 03:09:38 pm
Hey, all you engineers out there,
I just took apart an electric piano (Casio CTK-500) because one of the switches broke. I figured, if I can't fix it, I'll circuit bend it. I believe I will be able to fix it, so that's not really my question.

Here's how the switches work. There is a plastic block with metal contacts glued to it. The contacts ride on the circuit board below, connecting the right "tracks" together for a given position, but there is a ball bearing on a spring lined up with grooves to provide an artificial "detent" when moving the switch. There is some kind of grease on the contacts and on the circuit board. But, so many sources I've read have warnings saying NOT to lubricate electrical contacts. When I think about it, that does make sense for a number of reasons:
1. If the lube doesn't conduct well, of course the switch won't work well (or at all)
2. If the lube is conductive, it might let current go through paths that it shouldn't (in a multi-position or multi-pole switch) causing erratic or unexpected operation, or worse, the lube could "run" or "creep" into areas where it shouldn't be and connect two things that shouldn't connect, ruining the device. Over-lubricating mechanical components can also have this effect if the lube "runs"
3. A lot of lubricants (oil in particular) are flammable. Flammable liquids probably aren't a good thing to have around a powered circuit.   smiley-grin
4. Many lubricants attract dust and grime over time, and dirty contacts make for poor/intermittent connections.

With all that in mind, I was somewhat surprised to see the contacts greased like they are. At least there's not too much where "creepage" would be a problem, but how does it allow the contacts to work, without shorting the tracks at the same time? Having said that, I am somewhat surprised, based on the mechanism employed (metal contacts sliding on a circuit board) that the switches haven't had more problems, even with lubrication. The piano is around 16 years old.
5  Using Arduino / General Electronics / Re: LM317 regulating voltage but no current! on: February 10, 2013, 05:30:02 pm
Remember the golden rule: If so many things are wrong that you fail to understand how they can be so wrong, check the ground connections smiley-mr-green

Also, make sure the regulator isn't getting hot when it's sitting regulating voltage w/o load (and with load as well) because the LM317 has thermal overload protection to protect fools from themselves. If it is getting hot, use a heat sink, even an alligator clip on the top may do the trick! Remember, the bigger the difference between the input and the output voltage, the more heat is going to be dissipated. So, if you're regulating 30 volts down to, say, 9 volts, you'll be putting out a lot of heat even under a small load.

One more thing, look at *THEIR* example circuits on the data sheet ("they" being the makers of the voltage regulator) and compare them with yours.

If all else fails and you're sure your circuit is correctly wired (or you've corrected any "mistakes") then it's possible that the regulator is broken (age, prolonged overheating, incorrectly wired on power-up, etc.)

Often when I'm shopping for electronic components, if they're cheap enough, I'll get one more than I need in case I break one.  smiley
6  Using Arduino / Motors, Mechanics, and Power / Resistor in series with MOSFET gate? on: August 19, 2012, 11:07:01 am
Hey, this is just a quick question.

On another post, I was having trouble with a mosfet and a motor and I mentioned the fact that I just had the output line hooked directly to the mosfet. Someone recommended having a 100-ohm resistor in series with the gate. What is the purpose of that? Is it just to protect the arduino in case you connect the wire into the wrong hole on the breadboard (e.g. the drain of the mosfet instead of the gate?) I had one of those "inductive spike suppressing" diodes. I thought that the fact that the gate is isolated and controlled by voltage instead of current was the advantage of a mosfet over a regular transistor.
7  General Category / General Discussion / UL listed appliance with no fuse? How can this be? on: July 04, 2012, 11:07:41 am
I recently took apart a fan for someone who wanted me to fix it. It was UL listed according to the label on the back. However, I took it apart and I discovered that the motor is NOT protected against over load in any way, shape or form. A motor that has gummed up lubrication or failing bearings can eventually seize and this causes the motor to be "stalled" i.e. attempting to run but not able to turn. A stalled motor usually draws excessive current (but not enough to blow a 15 amp fuse in the electrical panel!) and this can overheat the windings, which damages the motor, and at higher voltages (such as from the wall socket) this could cause a fire!

Now, I'm fairly certain that since a stalled motor draws more power than a normal one, a properly sized slow-blow fuse would blow before a catastrophic failure occurred, right? Sure, it could blow due to a temporary condition such as a kid sticking something in it, but I'd rather put in a new fuse (or even get a new fan) than have my house burn down because I failed to periodically lubricate a <$20 fan! A thermostat mounted to the (usually metal) case of the motor would also work, though that might be more expensive than a fuse.

The scary thing is that the fan claims to be UL listed! How is that even possible? I thought UL was a SAFETY certification! How can an appliance with an unfused, non-overheat-protected 110v motor possibly meet any kind of safety standard??? Seriously, I'd hate to see an appliance that ISN'T UL listed! Does UL no longer even so much as look inside the appliance before approving it? How bad would it have to be to NOT be listed?

Besides, what bean-counter decided that they would rather face a wrongful death lawsuit due to a fire than raise the cost of the product by a measly 25 cents???
8  Using Arduino / General Electronics / Low battery voltage detector? (9v total battery voltage, 5v regulator) on: June 11, 2012, 12:53:40 pm
I was going to try and make a low battery voltage indicator using an LM339, and after I figured out the circuit itself I would connect it to an Arduino input, and make my program to give a visible indication of a low battery. What I was going to attempt was to have a 5v voltage regulator connected to "input 1 minus", using a voltage divider circuit with a 10-ohm resistor and a 4.7 k, to make the voltage go down by a very small amount. (voltage drop of like 0.1v on the 10 ohm resistor). Then, the 9v is hooked to a 2.2K resistor, then to ground through a 4.7K resistor, with the "input 1 plus" pin connected in between them. I use a 5k potentiometer to simulate voltage changes. The output can only sink current, so I have an LED wired to 5V, through a 470-ohm resistor then to the output.

The circuit does not seem to work as I intended. I wanted to voltage-drop the 9v through resistors to be close to 5v, so that when the battery voltage started to drop, the voltage that the chip would see would be lower than the reference voltage, causing the output to change. My LED just stays on all the time until the voltage is too low to actually light it up. That's not exactly what I'm aiming for. Am I missing something here? This circuit is currently on a bread-board by itself, I just wanted to figure out if my idea worked. So far, it doesn't.

If you use a series resistor voltage divider circuit, could you bring the battery voltage within the range of the analog inputs on the Arduino, and then just use the analog read function to check the battery level?
9  Using Arduino / Motors, Mechanics, and Power / Re: 9v Motor + Mosfet + Arduino = timing errors/crashes? on: June 05, 2012, 05:32:50 pm
Thanks. In an electronics class that I took previously, we were told that putting capacitors in parralel will result in increased total capacitance. I have a number of different values and about 6 of each, so I will add a 470 uf cap between 9v and ground, in addition to changing the batteries. If that doesn't help, I'll hook a few more caps in parralel with the 470 to increase the total capacitance and thus the noise/sag supression capability.
10  Using Arduino / Motors, Mechanics, and Power / 9v Motor + Mosfet + Arduino = timing errors/crashes? on: June 05, 2012, 11:01:16 am
Hey everyone

I just recently got an arduino along with a bread-board and some additional control circuits (and of course a power supply, in my case it's just an AA battery pack, 6 AA's, which add up to 9 volts) and I made a circuit where there are 3 leds, controlled by the arduino. I hooked diodes on two of the outputs because I wanted to make the Mosfet, and thus, the motor, turn on when two of the lights were on, but not when the third light was on. I didn't have anything else hooked up because I just wanted to figure out how to control a motor with an Arduino, before I tried to combine motor control with more interaction. The LEDs change at a pre-determined interval, that doesn't use the delay() function, because I know delay() prevents the arduino from reading any other inputs (except interrupts).

It worked fine for a while, and I experimented with other ideas, then re-set up the same system again and re-loaded the program.
The problem I'm currently having is that occasionally, the starting and stopping of the motor causes strange things to happen. Sometimes, the LEDs appear to miss a step or change out-of-time, other times the arduino seems to crash and require a power cycle or a press of the reset button.

I have a diode to prevent a voltage spike from the motor from damaging the mosfet, and I had that last time as well. The mosfet's gate is connected directly to the two outputs (through diodes) without a resistor.

I have been using the same battery for a while and I'm wondering, could a low battery cause timing errors or system crashes when something like a motor turns on and off? Since I haven't had the arduino for that long, I don't know what the effects of a momentary voltage sag are. My other question is, if it's not likely to be a battery problem, would adding a cap between 9V and ground (on the breadboard) help? Or, should I use an external 5V voltage regulator with decoupling capacitors and attach that to the 5v input of the Arduino? (provided, of course, that I verify that the voltage is correct) because I thought the arduino had caps on the board already! Are those not big enough to smooth out the kind of noise that a motor might generate? The biggest caps I have are 470uf, 25v (my battery is only 9v)
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