lcd 1602 scramble near halogen lamp.[ solved ]


I got trouble with a arduino minipro and 1602 lcd, I get scramble text randomly, I thought it was, on the display. But after some time I discover that all time i turn on or off an halogen lamp on my desk it happens.
So, any way to filter interferences caused by the lamp ? capacitor, ferrite, coil, ect, to avoid that.
I used this schematic:

Thanks in advance.

You need some filter caps on your +5V power bus, probably at least 1uF to 470uF . The garbage is caused by spikes on 5V bus when the mains voltage dips. I have seen something similar with my halogen desk lamp but eliminated the problem by adding caps on my +5v bus.


Thanks for your help and suggestion... but no result, I tried some caps from 2.2 up to 470 uf and every time I switched the lamp on off it scramble the lcd. Since the first time i suspect voltage interference-dips issue, with the lamp, but with caps and even powered the circuit with battery cells, i got scramble. So I pushed the lamp to to end of the desk and ... no more scramble. So electromagnetic issue ? To test I used a piezoelectric lighter with no gas, put it just near the LCD and press the push button a couple of time... and... scramble again... So my conclusion, poor lcd getting interference from any hight level electromagnetic device cause that scramble. Solution get rid of my halogen lamp and get a LED new one.

Thanks again.

Well deduced.

There are two reasons why "dips" in the mains supply are not going to affect the Arduino; one is that the power supply to the Arduino should filter out such "dips" and especially so if it is a switchmode supply which usually has considerable reserve.

The second is that a desk lamp is not going to cause such a "dip", whilst the vacuum cleaner, washing machine or a power tool well might; it is very much a matter of magnitude.

So it clearly is electromagnetic induction. The base of the halogen lamp contains a moderate size power transformer (though they will be moving toward switchmode supplies now), and switching it on or off will create some magnetic transients. A major problem is if you are using a breadboard and "jumper" wires, as you create loops of significant size in the wiring which pick up such magnetic transients which may be measured in nanoseconds. A physical switch is particularly good at creating such impulses, the more so if a spark is produced. Sparks were the basis of the "early days" of wireless transmission.

LCD displays appear to be particularly susceptible to such interference, judging by the frequency of such problems reported here.

So keep your wiring "tight" with wires to each location bunched together.


Thanks Paul.

I used 3in wires -+8cms, short ones from the LCD to arduino, from that elements was moderate influence. And when i tested with the piezoelectric lighter the scramble only occurs when i pressed it under the glass of the LCD close the PCB. As you say, halogen lamp have lot of coil of the power transformer from 220v to 24v will get a bigger electromagnetic induction than my lighter.

Thanks all.