Does this "Arduino" signal indicate a faulty board?

[chipwitch]

I thought I'd try one of those generic Arduino clones and settled on the "Funduino."  For $17 I thought, what the hell.  It arrived yesterday and a quick test seemed okay initially.  It accepts uploads without issue.

The board is based on the Atmega2560.  The sketch is the typical "Blinky" modified to approx. 2 Hz (250ms high, 250ms low).  The on-board LED flashes as expected. For those MCU programmers unfamiliar with Arduino, the on-board LED is tied to the board's pin 13 (digital).  Pin 13 is also the output pin for the "Blinky" sketch.  Anyway, the photo shows a less than stellar square wave.  My genuine Arduino board is currently unavailable for comparison, but I'm guessing the wave should actually be square?  If defective, what might cause this output?

[Rigby]

Do you know for sure that the default sketch on that "Funduino" is meant to produce a square wave?  I'm not doubting you, I just know that those clones can have weirdness in the default sketch.

If you've uploaded your own blink routine (sounds like maybe you have) then this is definitely not the wave I would expect to see with digitalWrite(13, HIGH); delay(1000); digitalWrite(13, LOW); delay(1000);...

[nuhamind2]

probe properly compensated ?

[chipwitch]

Thanks... No... you're right to ask.

I uploaded the modified Blink (not "blinky") sketch from the Arduino IDE examples.  I modified the delay.  Either way, I get the same wave form (time component altered, of course).  I also re-uploaded the bootloader.   See, I had my doubts too.   

Also, I should have mentioned there is nothing externally connected to the board (output or input).  And, the power source is a 9V battery.

[chipwitch]

probe properly compensated ?

I'm new to scopes.  I don't know what that means.  If you're talking about the "cal" knob, it's turned all the way to the right and "clicked."

[Svuppe]

To me it looks like the scope is AC coupled. Try DC instead.

[chipwitch]

To me it looks like the scope is AC coupled. Try DC instead.

    That was it!  Thanks!

[madires]

probe properly compensated ?

I'm new to scopes.  I don't know what that means.  If you're talking about the "cal" knob, it's turned all the way to the right and "clicked."

He's talking about the compensation trimmers of the probe itself. Most probes got a compensation trimmer for low frequency signals (in the handpiece of the probe) and another for high frequency signals (in the small box with the BNC connector). I don't know your scope but it might have a squarewave output for adjusting the compensation trimmers of the probe. Please check the manual of your scope or probe for the correct procedure.

I concur with Svuppe, please check which input coupling you've selected.

[nuhamind2]

The first time i use oscilloscope,i define probe compensation as "making square wave look square".Feed your osc with square wave output from your osc then adjust the screw on your probe until it looks the most square.

[chipwitch]

The first time i use oscilloscope,i define probe compensation as "making square wave look square".Feed your osc with square wave output from your osc then adjust the screw on your probe until it looks the most square.

Yes, I remember now doing that when I first got the scope.  Forgot about the internal "probe adjust" signal.  Thanks for the reminder.

[pickle9000]

Things to check

- Is your probe calibrated / compensated? Connect to the test point as in the image, Set coupling to dc. If you see a nice square wave then the probe is calibrated. If you don't there will be a small adjustment screw near the BNC or on the probe handle. Hopefully you will have the little driver that came with the probe to adjust it. The driver is normally plastic or plastic with a tiny metal bit in the end. Just adjust until the probe looks good.
- From time to time check to make sure the ground on the probe and scope is good. Check from the outside of the BNC to the ground clip (continuity). For the scope unplug the scope and check from the outside of the BNC's to the ground pin on the plug (continuity).
- Safety note - Poking around mains voltages, switching/ computer power supplies can fry your scope and hurt you so leave that alone until you read up on it. Most beginners will not have the equipment to do that in relative safety.
- Make your measurements with your probes set to the x10 position. Your scope may also have a switch that needs to be set so you can read voltages correctly. This reduces the impact the scope itself will have on the reading.

On to your signal, make sure you have your coupling set to dc and your probe has a good ground connection. You may also want to disconnect your LED to see if it is having an effect.