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[on:]

Hi all,

My first post here so I hope this is in the right section.

I'm not an electronics engineer so please bear this in mind.

I've just built my first project using an Arduino Mega for controlling my aquarium lights.
My project includes the following:
Arduino Mega [1280]
18x 3W Cree leds via 6 buckpucks [6 strings of 3 leds]
16x2 LCD
DS1307 Real Time Clock
10k thermistor
2 Akasa 80mm 4-wire PWM PC fans
1 photocell (this is used to change the info. displayed on the lcd by waving your hand across it)
1 BC546 NPN transistor (used to turn on/off the lcd backlight)

Whilst writing my sketch I did lots of testing with all the above on a breadboard and didn't notice any problems but since I've moved all the above into my aquarium hood (which is close to the central heating boiler) I've noticed that when the boiler turns on/off I'm getting corruption on the LCD (random charcters) and it seems like the sketch stops running properly.

Now, I must point out that everything runs fine if I remove the power to the fans so it appears that the boiler is affecting the fans which is causing the problem ??
I have extended the fans cables to about twice their normal length (if that's important) and the Mega and the fans are powered by 2 different psu's with the Gnd from both connected together. I'm reading fan speed using 2 interrupts and and adjusting fan speed using PWM as the temperature changes.

Can anyone help me with this (what appers to me) 'odd' problem as this is way beyond my limited knowledge.

[Reply #1 on:]

The boiler relay is putting out lots of electromagnetic noise when it switches, you need to reduce your circuits ability to pick up noise.  This might be as simple as putting ferrite toroids over all the leads where they enter the Arduino, or alternatively improving the grounding (putting it in a metal box?)

http://en.wikipedia.org/wiki/Ferrite_bead

What basically happens is that long cable runs act as radio aerials - relays and switches carrying large currents act as spark transmitters when switching off.

[Reply #2 on:]

You could even just be picking up line spikes and noise if your power supply isn't very filtered.  When the boiler kicks in (the pump I am assuming) something of that draw can bounce the line voltage pretty badly.. are you using the same power supply as in testing?

Try using a DC source (like a battery) to drive the arduino, and see if still occurs.  Ditto on the LED's if you can.

The solution is as simple as a ferrite (like above) or a nice smoothing capacitor after the regulator, if it's just power noise.  If it's induced power because of the lines, a ceramic cap to ground may be the answer.  In all cases, it does sound like a power noise problem, so isolating where it's coming from will determine what and where..

[Reply #3 on:]

Thanks for the replies.
I will definitely look into the ferrite beads but could you give me more info. about the capacitors as I'm not sure where to put them or what value to use. Is it worth trying the capacitors aswell as the ferrites or should I do one thing at a time ?

[Reply #4 on:]

It seems like your boiler circuits could need some "overhaul"(not sure about the right word here) it should not affect other electrical equipments.
But, it is easy to build long antennas like MarkT pointed out.

My suggestion is very easy and very effective.
1. do as focalist suggest, filter your dcpower. 1 Elyt 220u-470u + 1 ceramic 10n.
2.Twist all your wires, from power down to signals. In cables mentioned as twisted pairs.
eg a +signal twists with a gnd and so on.

And also think of it as all current that flows out through a wire with some area should have the same area to return in, they should together be your twisted pair.

 It is only in cars u ground in body and we all know what a nightmare it can be to find faults there.

thank you

[Reply #5 on:]

See...

http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html