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16  Using Arduino / General Electronics / Re: Serial communication failure when using power supply on: February 28, 2013, 11:49:10 pm
Will try the capacitor trick for the reset, i heard the resister doesn't work on uno r3. Could very well be a reset problem. I am now testing an unregulated 7.4v supply (puts out 10.3v under arduino load), and so far no resets, but it hasn't been a long time yet. I don't think it's my machine since I've had the terminal open for hours normally without any issues.
17  Using Arduino / General Electronics / Serial communication failure when using power supply on: February 28, 2013, 11:32:17 pm
I'm working on a project that requires the arduino uno r3 to be powered by a separate power supply AND have the usb cable connected to a PC for serial communication. When using a separate power supply, the board will reset sporadically and serial communication will fail after a few minutes. To isolate any cause I have disconnected all wiring from the arduino pins, and am just running a bare board. It still resets randomly and has serial communication failure when using the separate power supply. Any ideas where I can start troubleshooting this? The tx/rx lights still activate when it has failed, but my terminal receives nothing. Thought it might be a grounding issue but I measure 0V from USB ground to the barrel -.

My search terms for this problem brought up nothing, but I think I remember reading something about people frying their uno r3 serial chips by using a separate power supply while having it plugged into USB.

EDIT: Power supply is 12V 1.5A regulated. Reads 12.3V on a dmm. under arduino load, 12.27v. I will attempt using a different supply but suspect the problem will remain.
18  Using Arduino / Project Guidance / Re: Reset/reprogramming behavior on: February 25, 2013, 10:32:33 pm
Thanks for the info. I'll look into ICSP.
19  Using Arduino / General Electronics / Re: Best setup for 12v solenoid on: February 25, 2013, 10:12:45 pm
Yea, I will have to test it again once I get the fet and solenoid. If it gets too hot I'll just use two supplies, or maybe find a way to heatsink the vreg.
20  Using Arduino / Project Guidance / Reset/reprogramming behavior on: February 25, 2013, 10:10:22 pm
I'm working on a secure access project controlled by the arduino. One of the project requirements is a way to communicate with the arduino. I figured I'd use the usb since that was already built in, however that obviously raises some potential security problems, as in the code could easily be reprogrammed via the usb port. My question is, if auto reset functionality is disabled, via the capacitor or cut trace method, will this effectively prevent the atmega chip from being reprogrammed through the usb cable? I know it can still be done by holding the reset button, but that won't be a problem since the arduino board will be inaccessible.

I guess a better approach would be ethernet shield/wireless some other way of communication. I'd rather keep the component count optimized, however. From my experiments it seems with the capacitor between reset and ground, there is no longer any way to reprogram the board through the usb cable, even when cycling the power to the board. Can anyone confirm?
21  Using Arduino / General Electronics / Re: Best setup for 12v solenoid on: February 25, 2013, 02:46:03 pm
Hmm, my previous experiences with running 12v to the barrel connection was the vreg got really hot, even when only powering a couple LEDs limited to ~5ma each. I will attempt it again though to see if I have better luck this time. If not, I'll use two supplies. I don't have a 5v switching regulator around, that would be the ideal solution to bypass the vreg entirely, though I'm not sure if that would introduce em noise problems.
22  Using Arduino / General Electronics / Re: Best setup for 12v solenoid on: February 25, 2013, 01:05:47 pm
I thought so, but wanted to make sure. Thanks
23  Using Arduino / General Electronics / Re: Best setup for 12v solenoid on: February 25, 2013, 11:11:42 am
Got it, so optoisolation isn't really necessary then. Is it that hard to set it up so a HIGH output on the pin correlates to the solenoid being activated? Seems a lot of setups have it so you need to set output on the pin to LOW to switch the solenoid on.
24  Using Arduino / General Electronics / Best setup for 12v solenoid on: February 25, 2013, 10:55:47 am
I am trying to figure the safest way to have the arduino activate a 12v solenoid. I've done a lot of reading up before posting, just had a few questions.

1) Two separate power supplies are needed, a 12v one for the solenoid, and the arduino one. I don't want to use the 12v for the arduino because the vreg will get very hot.

2) I will need to tie the grounds together. I heard this can lead to issues like backfeeding through the mcu pins and possibly damaging it. I tested with my multimeter and the potential across the two - for both supplies was around 48v AC. Apparently this kind of measurement is normal from what I read, it's just a matter of bringing grounds to the same potential.

3) It seems a mosfet is the best way of switching the 12v side. I don't know if this would protect the mcu pins well though. Using a relay instead of a mosfet still gives problems with current usage of the coil along with needing another diode, (The other one being across the solenoid) so it makes sense to go with a mosfet instead.

4) Optoisolating the 5v and 12v sides might be a solution, but is it necessary? Is there a decent optoislation chip anywhere? There was one on sparkfun but it was limited to 50ma, not sure if that would be enough for switching the mosfet? I saw this solution here:
25  Using Arduino / Project Guidance / Re: Weather Station and Solar tracker on: November 04, 2012, 03:00:49 pm
Umm, some people do like actual data. Otherwise, there wouldn't be a market for weather stations at all, nor would there be ASOS stations all over the country.
26  Using Arduino / Project Guidance / Re: Weather Station and Solar tracker on: November 04, 2012, 02:17:22 pm
I'm making a similar project, but without the wireless part. I really wanted wireless but the climate here just won't allow it. It can stay below freezing for months in the winter and I know even with a SLA battery I'd have power issues in that kind of prolonged cold. Plus, the sun can disappear for weeks here. Therefore I ended up running 100ft of cat5 to my outdoor sensor station, and dropping the clock rate for the sensor communication, given capacitance issues and such caused by the long cable.

I'd also be careful about program memory. Mine disappeared fast when adding an ethernet shield and code to communicate with the multiple sensors, and I had to upgrade to a mega, which I am waiting to arrive before continuing my project. You might want to just get one of those instead of the uno and save the trouble of running out of space.
27  Using Arduino / Project Guidance / Re: Need Help Choosing 110V Relays for Mega 2560 on: November 04, 2012, 02:08:47 pm
Be careful with EMI issues. I am not sure if the relay board has EMI suppression and flyback diodes built in, but you might have to add those and some MOVs if the inductive loads wreak havoc with the microcontroller. I would assume a relay board would take these into consideration, but you never know.
28  Using Arduino / Project Guidance / Re: memory woes on: November 02, 2012, 02:14:28 am
No idea about the pi. I'm better off staying with the arduino than switching horses midstream. I'm sure I can put the uno to good use on another project anyway.
29  Using Arduino / Project Guidance / Re: memory woes on: November 02, 2012, 01:05:29 am
I (wrongly) figured my project was simple enough to run on an uno. I didn't take into account the massive overhead the ethernet and sd card functionality incurred. I looked at the pi, in many ways it does seem to be better, but it's out of stock through the normal distributors right now. It has less GPIO pins than the uno, however this is offset by the built in sd card and ethernet (since those take up pins on the arduino). Also, since the pi runs an actual OS, there would be the complexity of ensuring my application started up correctly and ran the way I wanted, etc, which is avoided on the arduino. Granted, I haven't done too much reading up on the pi so I could be wrong on that. If I had known about the pi back before I started this project I might have gone that route, but at this point I'm invested into the atmega mc.
30  Using Arduino / Project Guidance / Re: memory woes on: November 02, 2012, 12:38:38 am
Ok, so all my optimization tricks weren't enough, and unless I want to severely cut back on the features I planned on, I need a different board. Found the mega on sale for $40 so decided to grab that, should be here next week. I would have preferred the 1284 chip, but when I factored in the added expense and time of trying to get a bootloader on it, buying an FTDI adapter, etc, the mega at $40 seemed like the better deal, even though it only has half the SRAM of the 1284.
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