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1  Using Arduino / General Electronics / Re: Supercap with dc buck converter question on: February 26, 2014, 01:38:50 pm
Thanks. Helpful information, a bit disappointing to find out it's a lot more complicated than I originally envisioned, but I'll figure a way I suppose. I didn't want to have to separate the shield from the board but it appears that is a necessity. I've successfully used a 1000 uF cap to write the critical variables to eeprom without the ethernet shield (when 5V rail drops below 4.8V it writes to eeprom), so it's really a matter of finding a way to get it working with the shield - separating it means I can go back to the 1k uf cap and not worry about exceeding the buck converter output capacitance rating.
2  Using Arduino / General Electronics / Supercap with dc buck converter question on: February 26, 2014, 12:13:08 pm
I have a project that requires use of a dc to dc buck converter for a couple reasons:

1) needs flexible input voltage of 12-24V which built in linear regulator cannot handle

2) Uses ethernet W5100 which consumes ~200ma, which makes the linear reg run very hot at 12V.

In order to efficiently utilize eeprom lifetime, I'd like to move some critical variables to a "write on power failure" scenario. This of course requires that the power failure is detected and also that there is enough time to write them to eeprom. Given the ethernet consumption of 200ma, sufficient time to write to eeprom requires a large capacitance. I figure a 1F supercap is plenty, however reading the datasheet of the buck converter (http://www.digikey.com/product-detail/en/OKI-78SR-5%2f1.5-W36-C/811-2196-5-ND/2259781) shows a maximum output capacitance of 3300uF. Unless I'm missing something,  it appears I cannot use the supercap to power the avr for this situation as it would be far too much capacitance for the buck converter to deal with?
3  Using Arduino / General Electronics / Re: Freezing problems when power switching. on: August 05, 2013, 01:22:21 pm
EMI problems are extremely frustrating and really hard to pin down. I've been battling with one myself over several months and have made no real headway. At least you've managed to isolate and track things down to some extent. I would try to put the arduino in a faraday cage (metal box) which is connected to its ground next, and then see if the problem still happens. That won't solve things if there are transients on the opto lines but should at least eliminate induced EMI as a cause. If it still happens, it would be interesting if you could try to capture the offending transients on a scope hooked up to the arduino side of the optos, it would at least show which lines the transients are occurring on.
4  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: April 12, 2013, 11:48:49 am
I hate to seem like I keep bumping this or whatever, but I did want to share what I found out from my extensive troubleshooting on this problem, hopefully it's helpful information to anyone with a similar issue.

I've now had things running without any serial port crashes for over a week. I cannot say for certain what exactly "fixed" the problem, but it was one of two things:

1) I added a MOV in parallel with the mini fridge to get rid of the inductive kick when it switches off. Even though I moved the fridge to a different circuit and the other 120V leg, I still noticed a clear correlation between when it shut off and noise on the serial port.

2) I needed to get a new case for my desktop system since a video card I was upgrading did not fit in the old one. Obviously this changes the grounding characteristics and etc of the system. It's possible the old case had a fault that caused random noise on the USB ports.

I strongly suspect the MOV is what solved the problem, but I have no way of knowing since I don't have a scope. I'm sure this would have been a lot easier to track down if I did have one. Of course I'm still not 100% certain it's truly fixed either.
5  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: March 29, 2013, 12:52:22 pm
gah. so annoying. It's still happening even when moving the mini fridge to a separate circuit and leg (it's now on an outlet which is on the other 120V AC rail). At least it doesn't happen as often.

Would be useful if there was a software way to restart the usb port in windows without physically unplugging the USB cable. Then at least I could detect the problem and solve it programmatically.
6  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: March 24, 2013, 03:19:13 pm
Problem is back from the dead again  smiley-confuse

Though it's not occurring nearly as frequently, it's still happening. I've noticed a lot of "serial noise" on the arduino through the fact that it executes a command occasionally. The command is executed upon receiving a "0" over the serial stream. Yes, probably not a good idea for that to execute a function, so I should change the code for that.

Some interesting things I've noticed:

- My desktop PC randomly powers itself up when shut off. I suspect this is related to the same EMI issue that is causing the arduino to get serial noise and corrupt the com port in windows. Wake on LAN is not turned on. Probably some kind of EMI causing the ATX power on signal to go high. Solution right now is turning off the switch on the ATX power supply.

- The serial noise sometimes corresponds with an inductive load (mini fridge) cycling. This fridge is on the same circuit but a different outlet in the room. Might be related perhaps.

- Sometimes the serial noise occurs when the PC has been powered off and I then switch the ATX switch to on.


Wish I could track this down. I don't have a scope, and suspect in order to really get any further I'd need one. I will try taking the mini fridge off that circuit, however, and see if that makes any difference.
7  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: March 15, 2013, 12:37:08 pm
Ok, so it's now at 40 hours uptime, and still no serial port crashes. I think the problem is truly fixed. Still not exactly sure what the cause was, however the fix came via a combination of enclosing the uno in a metal box attached to ground (EMI suppression) and changing the USB cable. I noted the old USB cable had an issue with its ground, the resistance was unstable. It varied from ~70ohms to over 300ohms. That could definitely cause problems. Swapping with a normal USB cable (0.2 ohm resistance in ground) seems to have fixed the problem. However, one of the first steps I tried before was swapping that cable, which didn't fix the problem at the time. So, I believe there were also some EMI issues which the metal box seems to have resolved nicely now. Hopefully this information is helpful for anyone else who runs into a similar situation.
8  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: March 14, 2013, 08:17:16 pm
Problem "appears" to be gone now after a change of USB cable and 24 hour run on the win7 machine. Not sure if I've run it long enough to get a conclusive result yet. The odd thing is I tried changing the USB cable before and it didn't help, so I'm not yet ready to say it's truly fixed.
9  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: March 13, 2013, 04:07:14 pm
Progress. The linux test had no problems with the serial port not working, it ran for about 24 hours and was just fine with the 12v DC power supply. I am now suspecting EMI issues, so I will be making changes to cable routing, as well as putting the uno in a metal box enclosure, and retesting on the win7 machine.
10  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: March 12, 2013, 06:14:08 pm
I'm currently testing on a linux machine. Uptime is about 30 minutes so far, no serial port crash yet. I tested earlier with a 12V SLA battery in place of the power supply. This also crashed the serial port after about 3 hours on the win7 machine. Hopefully the linux test is informative.
11  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: March 12, 2013, 12:44:19 am
Nope, no interrupts, the sketch is pretty straightforward and simple. And I've verified it's not being reset through use of an uptime counter. I still have to test the other machines though, but the weird thing is, it's very much power supply related, since I've ran it for over 12 hours without it crashing the serial port when there's no external power supply being used. Also verified on a separate mega r3 that the problem doesn't happen. Makes me want to try the older arduinos with FTDI based serial chips, but I don't have any of those unfortunately. When I'm able to test the other machines that should be insightful.
12  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: March 11, 2013, 01:25:34 pm
Ok, I wasn't sure if it was the board that was bad so I just tried swapping it with a mega 2560, and the same exact problem occurs. This is really weird. I would say "it's my computer" but for the fact that the problem never happens when the arduino is being powered solely from the usb connection.

I guess my next step is seeing if the problem occurs on a different machine. I have a vista and a linux machine to test. Should be informative at least.
13  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: March 10, 2013, 11:07:07 pm
Unfortunately, I seem to have spoken too soon. The problem is back, and it doesn't matter what power supply I use. As long as I use any power supply, be it switching or unregulated, serial communication fails after a period of between 20 minutes and 4 hours.

The failure happens either with the arduino's response not being received and its tx/rx lights staying solid for that duration, or, the com port in windows simply refuses to work anymore "A device attached to the system is not functioning." The only fix is unplugging and replugging the USB cable, and all is well again. Note, the uno does not need to be power cycled. I even put in an uptime seconds counter in my code to verify it wasn't being reset, and it isn't. So, it's a really strange problem. It only happens when using any power supply in the barrel jack. If I leave it on the usb connection for hours, there's no serial communication failure. I verified my circuit isn't causing the problem by running the trials without any connection to pins and a power supply directly into the barrel jack. At this point I am wondering if my board is somehow damaged. The 16u2 chip has rev 0001 on it, is that rev known for failures like this in windows?

It really seems like a waste to have to get an ethernet shield or some other way to communicate with the uno when there's an existing way already built in. It should work without failing like this, and requiring physical disconnection and reconnection of the USB cable to (only temporarily until it happens again) resolve.

Addendum: My code is flashed onto the 328p through the ICSP so there shouldn't be any reset problem being caused by DTR. As mentioned, I've verified via an uptime counter that the board is not being reset.
14  Using Arduino / General Electronics / Re: Best setup for 12v solenoid on: March 03, 2013, 11:00:24 pm
My tests so far with a 12v supply have led to no problems with the vreg even getting warm. It must have been the LCD screen's current draw causing the heatup on a previous project where I attempted to use a 12V supply.

Anyway, I noticed when the power supply is disconnected and the board is only powered through usb, there is still ~50mv backfed through the barrel jack. I'm afraid if the pin switches the fet in this state, the solenoid will attempt to draw a lot of current from the 5v usb supply back through the barrel jack, which might burn something out in the board. Do I need to take this into account, or is there some kind of limiting in the arduino board which will prevent this?
15  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: March 01, 2013, 12:20:05 pm
Looks like it was the power supply. I've tried using two others, and no reset or serial failures now. Really odd.
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