I keep blowing LCD 1602 modules!!!

[katzohki]

Look at this video, it includes information regarding the ground of your oscilloscope.

[22swg]

You cannot run the LED backlight on 5v without a limiting resistor ! min 10 Ohm  this should  be >. 5 w   

[David_AVD]

I think a schematic or at least a decent photo is in order.  Maybe the 7805 is becoming unstable (oscillating) at certain times.

[suicidaleggroll]

Have you tried skipping the 7805 temporarily, and using a current-limiting bench supply to drive the LCD instead?  What's the input to the 7805?

[tautech]

I have a fairly basic DSO (SDS 1102CML)
I suspected the 5V supply myself but I cannot see how this would coincide with me probing about with the DSO?

Don't under estimate the ability of the CML range. They are good little DSO's.

As has been mentioned, I'd suspect probing technique error too.
Make sure you use 10x and meter for a GND loop between the probe reference lead and where you intend to reference from.

[sleemanj]

Where did you get the 7805 you are using?

I have seen chinese 5v regulators (1117 series in this case) that fail with more than 10v input and no current draw, worse the failure shorts input to output!

[bktemp]

I have seen chinese 5v regulators (1117 series in this case) that fail with more than 10v input and no current draw, worse the failure shorts input to output!

TS1117 are only rated for 7V, so nothing wrong here if they fail at >12V.
Some manufacturers allow higher input voltages, but not all are equal.

[dannyf]

For the record, I have taken Chinese-made 1117 to 20v, and encountered no problem.

[sleemanj]

TS1117 are only rated for 7V, so nothing wrong here if they fail at >12V.

Trouble is they were sold and marked as AMS1117 which supposed to do up to 15v (and legit ones do).

For the record, I have taken Chinese-made 1117 to 20v, and encountered no problem.

Yep, some are fine.  But there are either fakes and/or parts in an datasheet I eventually found with the same part number but 10v max input (the ones I bought didn't mention this datasheet, just the official AMS one, the IC markings are the same, although the fakes ones are left shifted a bit).

Anyway, my point is, testing the voltage regulator is a simple thing to do, set it up on your breadboard with a small load, and wind up the input voltage to see what it can handle.

[wraper]

Maybe the 7805 is becoming unstable (oscillating) at certain times.

And this possibility rises the question if 7805 input and output are properly decoupled with capacitors?

[MAS3]

Multiple capacitors to be sure.
We really need to see some pictures and/or schematics to be able to give some advice that makes sense.
Oscillation is a serious problem, unexpected to a lot of people and impossible to see using a multimeter (even though a scope was involved here).

[dannyf]

We really need to see some pictures and/or schematics to be able to give some advice that makes sense.

"That's TOP secrete",

[MrRadish]

Thank you for all the responses so far.

I setup the test again with a 20x4 LCD that I received yesterday from a different source  to the 1602s I have blown . I also connected the DSO earth directly to the GND on the 7805 (The input to this is 12v)  instead of an arbitrary GND rail point on the breadboard. So far after 24 hours - no screen corruption and fully working LCD.

As for CCT diagrams - My CCT is based on http://arduinoliquidcrystal.readthedocs.org/en/latest/_images/LCD_schem.png with the exception that the ATMEGA is running on 3v3 and the backlight is connected to 3v3 without an external resistor (a resistor appears to be in place on the board?). The LCD itself is running from 5v

One further thing is that the 1602 blowing event may have coincided with me changing the controls on the DSO (eg V/div) or even switching it on (~80% sure). Could these events have caused enough GND ripple to blow the 1602 if they were sensitive or am I just blowing smoke 

[bktemp]

Please post a photo of your complete setup.
Changing settings on your DSO does not produce any spikes. Maybe you have a bad ground connection somewhere and the smallest vibrations on the table lift the ground pin of the 7805 and therefore it increses the output voltage because of the missing ground path. But without more details of your circuit it is impossible to say.

[22swg]

  and the resistor at from +5v to  +LED ?   

[Monkeh]

You cannot run the LED backlight on 5v without a limiting resistor ! min 10 Ohm  this should  be >. 5 w   

and the resistor at from +5v to  +LED ?   

There's a 100R resistor already on the board, and the backlight has nothing to do with the IC.

[22swg]

There's a 100R resistor already on the board, and the backlight has nothing to do with the IC.

None of the 1602 LCD's I have had have a resistor for the LED and I have had loads. there is a zero Ohm link sometimes . If LED array cooks ,  over current could take out the 7805 and supply 12v to his IC ? UC

Correction    One of my stock has 2 x 51 Ohm provided

[Monkeh]

There's a 100R resistor already on the board, and the backlight has nothing to do with the IC.

None of the 1602 LCD's I have had have a resistor for the LED and I have had loads. there is a zero Ohm link sometimes . If LED array cooks ,  over current could take out the 7805 and supply 12v to his IC ? UC

Take a look at the photo on the first page.

If the LED fries it will typically go open circuit.

[22swg]

Ooops    Didn't open the thumb, perhaps his BB wiring is at fault.

[suicidaleggroll]

None of the 1602 LCD's I have had have a resistor for the LED and I have had loads.

All of the ones I've used have had a resistor installed for the LCD backlight.  Just went to the lab to check on one of the ones there...yep, 6R8 (it's a 3.3v unit from mouser).

[22swg]

I checked too  4 LCD only one (4x20 blue) had R8 and R9 as 51 Ohm and in BL circuit . 

[MrRadish]

Please post a photo of your complete setup.
Changing settings on your DSO does not produce any spikes. Maybe you have a bad ground connection somewhere and the smallest vibrations on the table lift the ground pin of the 7805 and therefore it increses the output voltage because of the missing ground path. But without more details of your circuit it is impossible to say.

Ok so lesson for me - I will photo the project and put together the CCT diagrams next time I post asking for help  .

I pretty much rewired the whole thing yesterday including an LCD of a different make and supplier (as mentioned above). I have added a more robust GND for my scope and I even replaced the breadboard I was using just in case that was an issue.  All is working well.

As I have changed a fair bit I dont think I will get to the bottom of the issue but I think I was either experiencing a GND fault that caused the 1602 to blow or it was a faulty batch of 1602s. Why the DSO seemed to be linked I do not know. I consider myself to be scope competent as an ex RF engineer but this 5v thing is new to me ;-) 

If I can stomach the pain I may order a few more of the 1602s and give them another go out of curiosity.

Thank you all for your help.

[RobertHolcombe]

Maybe you have a bad ground connection somewhere and the smallest vibrations on the table lift the ground pin of the 7805 and therefore it increses the output voltage because of the missing ground path.

Have personally had this happen too many times using breadboards, it gets expensive fast 

[electr_peter]

I am running a ATMEGA328P at 3.3V on a breadboard along with some other sensors DH11, RTC etc. I am using the LCD1602A as the display for the time, temp and humidity. The 1602 display is running from 5V suppied from a 7805 and the rest of the circuit is powered by a 3V3 reg. The 1602 data lines are driven directly from the ATMEGA at 3V3. There are numerous decoupling capacitors spread around the circuit

What is providing power to the circuit? Power source could be shifted up/down w.r.t. earth/DSO ground.