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1  Using Arduino / Motors, Mechanics, and Power / Re: Urgent help needed - relay with load resetting Arduino on: November 16, 2013, 12:32:29 am
Hi guys,
have you ever managed to fix this issue?

I have a similar problem with a relay, car horn, and big 7-segment display all turning on during the time the horn is active!!
 
If you still read this thread I can give more clarification on the problem!

Thanks!

I did not resolve the shift register issue because it was just too unstable. I moved to a different solution of using an Arduino Mega, which gave me enough digital I/O's to construct a 25x25 matrix relay controller. It's been running fine over a year now.
2  Using Arduino / Motors, Mechanics, and Power / Re: Relay and back EMF on: April 29, 2013, 06:51:25 pm
Why not use an optoisolator ?

or was that ruled out?

Actually I have not tried an optoisolator yet. Do you have a particular IC in mind? I will buy one and try it. Thanks.
3  Using Arduino / Motors, Mechanics, and Power / Re: Relay and back EMF on: April 29, 2013, 01:21:33 am
Have you connected a flyback diode across the solenoid yet? The best place to put it is right at the solenoid terminals.

Thanks for the suggestion. I just tried it. It seems to help a bit, but the back EMF is still there as the Arduino gets reset from time to time.
4  Using Arduino / Motors, Mechanics, and Power / Re: Relay and back EMF on: April 26, 2013, 01:19:28 am
I have an embarrassing EMF problem. I forgot to pay attention to the 5V rail, which powers the relay, and the 12V rail, which powers the solenoid. Now whenever the solenoid is turned off, back EMF is generated, resulting in resetting the Arduino, which powers and controls the relay circuit board. Attached are photos of the PCB layout highlighting the 5V and 12V rails. As you can see, the 5V and 12V rails run parallel to each other, which is foolish. I have gone through cutting the traces on several of these boards, and found out that by cutting the 12V at the point shown in the photo, the occurrence of the back EMF is about 20%, instead of 100%.

Now even more embarrassing - I have 250 of these boards! I am wondering if there is a solution which involves cutting tracing and soldering, so I can salvage these 250 boards. Many thanks!
5  Products / Arduino Due / Re: shield layout for DUE/Mega on: March 27, 2013, 06:10:53 am
Found it: http://www.aqualedsource.com/prods/arduinor3screwshield.php

25 euro each. ouch.
6  Products / Arduino Due / Re: shield layout for DUE/Mega on: March 27, 2013, 05:52:52 am
Where can I buy one of the Mega Screw Shield? Thanks!
7  Using Arduino / Motors, Mechanics, and Power / Re: Relay and back EMF on: December 21, 2012, 01:24:44 pm
If you are driving the eBay relay module from the Arduino's 5V supply or from the same supply that is powering the Arduino, then the optical isolation is doing nothing useful. It's only helpful if the relay board has an independent power supply.

On your custom relay board, did you remember to include a diode across the relay coil?

Yes, there is a diode across the relay coil. Attached is the schematic of my 8-relay module. The diodes across the relay coil are D2, D4, D6, D8, D10, D12, D14 and D16. There are two inputs to each relay because I use a matrix configuration to control 256 relays. Please let me know if you see anything fishy. Many thanks.
8  Using Arduino / Motors, Mechanics, and Power / Re: Relay and back EMF on: December 21, 2012, 02:15:40 am
Try moving the Arduino further away from the solenoid and its wiring. In particular, that coil of red wire will create a varying magnetic field when the solenoid switches on or off, which will induce currents in anything close to it.

Also connect a power diode in parallel with the solenoid (1N4001 will do), or a snubber network across the relay contacts.

Many thanks. Removing the coil of red wire and placing the Arduino further away indeed did the trick. Using the relay module from eBay, the serial port connection does not drop after the solenoid is deactivated. Then I switched back to my own custom-designed relay module. The serial port connection does not drop, but the text from Arduino stops after about 30 seconds of activating/deactivating the solenoid. The main difference between the relay module from eBay and my own relay module is the addition of a photo-coupler for the eBay one. Is the photo-coupler recommended for the relay module? It seems to isolate the "noise" better. Thanks a lot.
9  Using Arduino / Motors, Mechanics, and Power / Re: Relay and back EMF on: December 20, 2012, 03:21:29 am
It sounds like a wiring or power supply issue to me. Post a photo of your setup and preferably a schematic too, then it will be easier for us to help.

Back emf is generated when the solenoid is switched off rather than on, and can be tamed by connecting a diode in parallel with the solenoid, cathode to positive end, anode to negative end.

Attached is a photo of my barebone circuit. The wires are labelled in red. Please let me know if you need more info.

One correction to my previous posting. The serial connection drops when the relay/solenoid is turned OFF, not ON as stated in my previous posting.

Many thanks!
George
10  Using Arduino / Motors, Mechanics, and Power / Relay and back EMF on: December 20, 2012, 12:49:39 am
Hi everyone,

I am debugging a garbage-character LCD problem which only happens when the relay is turned on and drives a 1A/12V solenoid. Initially I thought maybe my custom-designed relay board was the problem, so I ordered a simple relay from eBay:

http://www.ebay.com/itm/221162886568?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Then I stripped down my circuit to bare minimum consisting only of Arduino Uno, relay module from eBay, and the 1A/12V solenoid. All I do is turn on the relay every two seconds and turn it off every two seconds. What happens now is that when the relay is triggered and solenoid is active, I lose my PC's serial port connection to the Arduino. If the relay is triggered without the solenoid connected to it, the serial port connection is rock solid.

Is this normal for PC's serial port connection to drop when solenoid is active? It seems like back EMF to me. Your advice is appreciated.

Thanks,
George
11  Using Arduino / Networking, Protocols, and Devices / Re: Ethernet shield permanently returning 0.0.0.0 after working for a few hours on: November 09, 2012, 01:46:53 pm
Hi Gabriel,

Thank you for your update. I forgot to post my result back to the forum. I was using a wireless laptop as my server. After replacing it with another server using Ethernet connection, the connection failure does not occur any more. Regarding the 0.0.0.0 IP address, I bought a new Ethernet shield, and it's working fine. So it's likely the old Ethernet shield just stopped working.

Thanks,
George
12  Using Arduino / Displays / Re: Problem with LCD and Motor on: October 28, 2012, 12:00:58 pm
Quote
@nanohex, would you mind clarifying the ground flood for me? I am not too familiar with it. Thanks./

I couldn't come up with a decent explanation in my own words so this is from Wikipedia:

"A ground plane on a printed circuit board (PCB) is a large area or layer of copper foil connected to the circuit's ground point, usually one terminal of the power supply. It serves as the return path for current from many different components.
A ground plane is often made as large as possible, covering most of the area of the PCB which is not occupied by circuit traces. In multilayer PCBs, it is often a separate layer covering the entire board. This serves to make circuit design easier, allowing the designer to ground any component without having to run additional traces; component wire needing grounding is routed directly through a hole in the board to the ground plane on another layer. The large area of copper also conducts the large return currents from many components without significant voltage drops, ensuring that the ground connection of all the components are at the same reference potential."

Basically any area that's just left empty (copper etched away; no traces) is instead left with its original copper. These are then connected to ground.

Thank you for the explanation. It turned out that there is no ground plane on my relay PCB. Is there anything I can do?
13  Using Arduino / Displays / Re: Problem with LCD and Motor on: October 27, 2012, 02:06:48 pm
Hi dc42 and liudr,

Thank you for your advice. Attached is a closeup of the Arduino with labels. It should clear up some confusion regarding the wiring.

You haven't yet implemented the suggestion in my reply #59 because the power and ground wires to the LCD do not follow the same route as the signal wires.

Keep the +5v and ground wires to the relay separate from the ones to the LCD as far as possible. You shouldn't need to use the same ground pin for both because you have 3 ground pins on the mega. If the LCD and relay share the +5V connection, keep that shared wire as short as possible.

How are you driving the relay: through a transistor?

I will keep the LCD signal/power/gnd wires all close together.

Regarding the relay, it is powered by a separate 5V power supply. I am driving the relay through two transistors to provide a matrix configuration as shown in the attached schematic (containing 8 relay modules).
14  Using Arduino / Displays / Re: Problem with LCD and Motor on: October 27, 2012, 11:02:36 am
This may seem like a noob point, but I noticed your PCB doesn't have a ground flood? You should try adding one in to aid in heat-sinking!

...apologies if you already know this  smiley-razz

@liudr, I added the cap at LCD Vdd and Vss. Unfortunately the problem still exists. smiley-sad I will try cleaning up all the wiring and solder joints.

@nanohex, would you mind clarifying the ground flood for me? I am not too familiar with it. Thanks.
15  Using Arduino / Displays / Re: Problem with LCD and Motor on: October 23, 2012, 11:30:04 pm
This is the LAST time I am asking you: what happens if you just switch the relays without solenoids connected to the relays.

I would like to give you a definitive answer, but I can't. It took entire day to reproduce this problem once (with the solenoid connected). A few days ago I did disconnect the solenoid, and the problem did not occur for the entire day. However, it does not mean the problem would not occur without the solenoid connected. Until I find a consistent way of producing the problem, there is just no way to be sure.
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