May 19, 2012
about 2 months ago
Hey, they could keep track of how many of these things they have to sell. If they notice that they have a lot of these, they’d be like “Hey! We have too many grab bags! The pick and place machine must be broken again” =)
News - Designing for Graceful Fa…
about 2 months ago
For a consumer device, I would say a “good way to fail” would be:
1. In large type, put a very simplistic description of the problem. For example, in this case, it could be akin to “Sorry, the internal computer froze”. Or, if the computer itself thinks there’s an issue with the temperature sensor or some other part, it could say “Uh oh! The temperature sensor is busted!”
2. Don’t just say “Call (customer service)” for every error, but instead, give some “user maintenance” instructions, if applicable, (“Please turn the machine off and then back on” for a kernel panic) and then something like “If the problem occurs frequently, please contact (customer service)”
3. Put the nitty-gritty details below that message in smaller print.
A good example of varying amounts of “fault tolerance” would be vending machines and arcade games. Protecting the core function would mean greater profits for the owner. However, if the core function is impacted directly by the failure, a better (but likely more expensive) design would detect such a fault and indicate it to users somehow (display “OUT OF ORDER” or “Err” on the display, turn off the machine’s lights, etc) Although the technology to implement such things has existed for several years now, vending machines are usually built to last and/or be repaired, so many “dumb” machines are still in active duty.
I have seen a microwave oven that runs the fan for a little while after use, presumably to cool down the magnetron and transformer. However, said fan is on the same circuit as the light, so the microwave appears to still be running to someone not used to that model. (Albeit with the timer displaying “0”)
One failure mode I have seen on microwaves in the past is that the relay, or it’s driving signal, became stuck on, resulting in the microwave “cooking” constantly whenever the door was shut. With a normal microwave, this would be quickly noticed because the fan and light would also go on when you shut the door.
But if you became accustomed to the “fan cooldown mode” the microwave would APPEAR TO BE WORKING NORMALLY EVEN THOUGH IT IS SUFFERING A CATASTROPHIC FAILURE! In other words, you could be standing right in the kitchen, look directly at the runaway microwave, and then think it has stopped heating and walk away!
about 3 months ago
I use these boards for many of my projects. I have a roll of bare solid 22 (or 24?) gauge wire that I do point to point with on these boards. I’ll often make power “buses” as well, by having a bare wire next to some holes I plan on soldering components to later.
Some people use the legs of the components themselves to make short-distance connections. I have done so in the past, but I try not to anymore because I believe it would make future replacement of said component a royal pain. Other people like to just run over two holes they want to connect with a big solder bridge. This won’t hold together in the long term because solder is relatively brittle compared to an actual wire. It is also easier to see a broken wire than a solder joint that has separated.
This isn’t actually specific to just stripboards as the title would suggest.
about 3 months ago
For those who want to somehow protect their circuits from “epic failure” consider this. A fuse will not only protect your circuit, but it will appear “blown” (i.e. open) thus giving you a clue as to why your circuit isn’t working.
A PTC is more convenient because you don’t need to replace it, but because it is self-resetting, your circuit will appear “dead” but the PTC will still appear as a low resistance (maybe not a dead short) without power. However, it will be hot when powered and “activated” so you could do the “switch and feel” method if your voltages are safe to touch (most PTCs can’t handle high voltages anyway)
The voltage rating is kind of like the rating on a capacitor, in that you don’t want to use a (say) 32 volt fuse in a 110 volt circuit. The reason being is that the higher the voltage, the longer the distance that an arc can form. If the voltage is too high, the fuse cannot safely interrupt the current. An arc might allow current to just keep on flowing until something else fails, or the fuse could get hot enough to damage/ignite things around it (which somewhat defeats the purpose of having a fuse)
about 3 months ago
Just a word to the wise, if you are using resistors as heaters, I wouldn’t recommend running them at 10 watts if that is their max power rating. They probably won’t last long if you do that. 75% should be your max under normal conditions.
These are better for things like “dummy loads”, current sensing/limiting, and other medium to high current applications. Though they may work well enough as heaters, they may not be designed to deliver the majority of their heat to whatever they are attached to.
The wattage rating is more of an upper limit as to how much current/voltage you can run through it without breaking it, not necessarily a measure of their “heat output” as it would be for heating device.
about a year ago
What’s the input voltage? If it’s more than, say, 12 volts, it’ll get pretty darn hot. However, you’re in luck because the LM317 has built in thermal overload protection, so that if the regulator gets hot as a result of using the wrong AC adapter, or a downstream component failing shorted, it will temporarily shut down (technically it drops the voltage-it doesn’t shut off completely-but it generally has the same effect)
Run the numbers based on your input voltage (Vin - Vout) * Amps = Watts. In a nutshell, the bigger the difference between Vin and Vout, the hotter the regulator will get under the same current draw. At some point this will be too much, but as mentioned above, the regulator has thermal overload protection (Don’t ask me how they put that in the TO220 case) so it’s not going to ruin it, at least not right away. However, a prolonged or repeated overheat condition could still shorten the life of the regulator-hence the need for a heat sink.
about a year ago
You might be able to drive a transistor or a mosfet with this. Your current requirement is relatively low, so a small signal transistor will probably work as long as you remain within the maximum watts dissipated on the transistor. I would recommend picking a transistor whose maximum wattage is 25% to 50% higher than the normal load of the circuit. The cost increase would be marginal for this type of thing, and it will probably last longer.
about 2 years ago
According to the datasheet, it will work down to 2.7 volts at 8mhz, which makes this chip ideal for battery powered projects, since battery voltage goes down as the batteries die. Yet, it will also work fine at 5 volts (mine is running off of that and it hasn’t left a crater in my breadboard) so it could run directly off of 3 AA batteries (1.5 v * 3 = 4.5 for alkalines, 1.2 * 3 = 3.6 for rechargeables)
Of course, you could use 6 AA batteries and a 5v regulator, but who wants to use that many batteries? I use rechargeable AA batteries to power my portable projects and a 9v 1000 mA, UL listed DC power supply for my stationary ones (with the appropriate regulators of course)
BTW, http://hlt.media.mit.edu/?p=1695 has a solution for those who want to make smaller projects using the Arduino environment. This makes for a relatively inexpensive project if you’re looking to make a few small “light show” type devices and/or you’re good at multiplexing. Since the Arduino Uno can be used as an ISP, I recommend picking up one of those, because you’ll get to work with a pre-made board off the bat and then “graduate” to using one to program another.
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