Just a quick question: it safe* to keep the twatch running forever or should I conclude a fire insurance :) ?
*) in case I would have a suitable case
You should always have a good insurance :)
Assuming the twatch is assembled ok and the wiring is ok, you have the same risc as leaving a television or any device on standby.
the only difference between twatch and television is that twatch is a "dangerous prototype" :D
I would council you to treat it like a candle out of an abundance of caution. It is unfused, and not a certified electronic device, more a fun educational hack. I'd feel safer if it had a power supply fuse and the case should have proper ventilation.
should we start doing failure testing?
Hehe, thanks for the feedback guys. I just wanted to know if one of those components get awfully hot.
Currently it's in a very flamable cardboard box, so I simply hope I'll find a nice case before that room turns into toast :)
But the wallwart is fused and I'm a gambler anyway :D
The 5 and 3.3volt VREGS are the components to worry about. They have over current and over temperature protection, but I wouldn't risk my life on it :) They are through-hole TO-220 or SMD D2PAK, I forget which,but there's what they look like:
I did some investigations myself as I got the #twatch to use as a 24/7 server status display, rather than for Twitter.
I am using a 7.5V/1A wall plug switcher from Digikey, and I am using a Bud NEMA box #PN-1332C for the enclosure. (I wish I'd had the box before I posted this, but I didn't put it on my last order from them so I had to try again.)
This is a NEMA rated box designed specifically for these kinds of devices. Unless the LCD bursts into flames, it's very unlikely that the enclosure is going to be hurt or even browned by the regulators on the #twatch.
In free air, with an IR thermometer, 125 degrees F is the hottest area on the device, over the two linear regulators (no surprise). The CPU is around 90 degrees F, and the LCD surface is around the same temperature. I had the #twatch running for about two hours with the backlight fully on, before I took these readings. Again, I would have tested it in a case if I had one, but this was in free air (propped on my workbench).
This presumes a normal home or office environment, of course. My device will likely sit on my computer desk nestled between my router and my managed switch, behind the flatscreen. (I wish the person that started this thread would talk with Westell--you can make toast on the top of my DSL modem, it's that hot!)
I'm concerned about reliability more than safety, and maintaining the backlight's lifespan for the few years I will probably use the device. To that end, I'm thinking of modifying the board to use a power switch; turn it off when nobody's watching.
Other possibilities are to dim the backlight if no updates have been received in the past 10 minutes, or even to employ a rudimentary time-of-day routine to turn off the display from 0000 to 0800 local, say. It's very likely I'm going to rewrite the firmware for my specific needs anyway.
I feel safe running this 24/7 with the power supply and case I am using with it. Whether it will stay working for three years is something I don't know yet (anyone have a environment chamber?)
Thanks for the thoughtful analysis.
If you are monitoring, usually using the TCPIP interface to send stats from anther box, you should have complete control of the backlight from the computer sending to the #twatch. I imagine the backlight LEDs are good for 3 years of constant use, I have other LCDs that work ok running in similar circumstances.
I got my case, so I can do a followup.
The case I used (Bud NEMA box #PN-1332C from Digi-Key) is very similar to the one that Seeed Studios sells (ACC1319TB). It's wider than the LCD board by about 3/4" on both sides left and right and 1/2" wider on the top and the bottom. The depth of the case vs. the board is about 3/4".
In other words, there's lots of room around the board, particularly if you mount it on the transparent top cover as I'll probably do. The cover is gasketed, which won't be a lot of good if I put holes in the side for the ethernet and power cables.
I've been running the #twatch for a few hours propped inside the box. The temperatures haven't changed much from my initial tests in free air. What's most important is the big volume of air inside the box. I'm measuring 95 degrees F behind the board.
This seems to be nominal. A lot of overclockers would find these temperatures too cool! :)
In my other life in IT, I'm used to seeing board temps on workstations and servers be around 95-100F. I just measured the bottom of my DSL modem.
It's 107.5 degrees F.
Its power supply isn't even in the case; it's a wall brick like every other device. It had to have passed UL certification. I've had DSL for 9 years with that same modem and I'll never know why that modem didn't burn a mark on my desk.
The #twatch in its case is going to feel warm and I don't recommend wrapping it in a blanket. But I believe it'll be safe.