What is available to check a 40 mhz crystal oscillator signal?

Thread Starter

cstroh

Joined Jan 16, 2019
79
Is there anything available to check a 40 MHz signal from a crystal in a micro controller that will not bankrupt me?
 

Thread Starter

cstroh

Joined Jan 16, 2019
79
Thanks to you both for recommendation. SamR I just ordered the part you suggest. What did you use for probe or how did you connect to the oscillator?
 

Thread Starter

cstroh

Joined Jan 16, 2019
79
Now for the new posts. Thanks all. I just want to make sure the oscillator is working. It is tied to the xtal on a micro controller and the circuit which uses the microcontroller was unable to access and everything else seems to check out. I am not looking for accuracy at present, just want to know that it is working.
 

jpanhalt

Joined Jan 18, 2008
9,420
If you just want to know whether it is working, that is pretty much a given. Depending on the MCU a certain number of oscillations will be counted after POR, then an oscillator OK flag will be set.

However, you can make a counter and test whether the time between "ticks" matches what you expect for a 40 MHz clock. You can test that with any watch that has a second hand. Depending on the MCU, there are probably pre- and post- scalers. That way, using say a 16-bit counter (or more) you can get pretty close to 1 second per tick.
 

SamR

Joined Mar 19, 2019
2,126
It has a socket header to plug the crystal into to test it. Other suggestions are also good if you already have scope or frequency counter to use with a test circuit. For just a quick go/nogo check for a crystal the little board works well and is cheaper than the parts to build your own test circuit. Havn't tested for accuracy but agrees very closely with marked frequency on the crystals. Just a good cheap quick way to test them. Seem to remember a couple of pins that you can take to a scope or frequency counter to compare against the digital readout.
 

Thread Starter

cstroh

Joined Jan 16, 2019
79
Was hoping to test it while installed on the circuit board and connected to the micro controller. In regard to jpanhalt response. Can I do what you suggest while the micro controller is installed on the original circuit board with the crystal and if so what outputs on the controller would give me the info you suggest? And if I use a probe with an oscilloscope, do I put the probe on one leg of the crystal the reference to circuit ground or the probe on the one leg of the crystal and referenced to the other leg of the crystal? I do not have any short wave radio unfortunately.
 

Thread Starter

cstroh

Joined Jan 16, 2019
79
I also coiled a wire and connected it to my oscilloscope probe with the micro controller powered and held it near the crystal and got nothing.
 

MrChips

Joined Oct 2, 2009
21,123
Do not connect the grounding clip of the oscilloscope to any part of your circuit unless you are certain you know what you are doing. Doing so might end up making things worse, such as blowing up your circuit and your scope.
 

Thread Starter

cstroh

Joined Jan 16, 2019
79
My scope is a Hantek 6022BE and only connects to a laptop by a usb port. I pull the AC plug on the lap top and operate with the lap top battery.
 

MrChips

Joined Oct 2, 2009
21,123
Be in the know-how. Understand your situation.

1) What is your MCU (microcontroller)? How is the MCU (board) being powered? Is it a wall adapter? Does it have a 3-pin plug? Is the grounding pin properly grounded?

2) What is the brand of your oscilloscope? How is it being powered? Is it a wall adapter? Does it have a 3-pin plug? Is the grounding pin properly grounded?

3) Using the probe on the oscilloscope, touch the tip of the probe with your finger. Do you see a nasty looking 60Hz AC waveform? Touch the tip of the probe to any part of the MCU circuit. Do you see a nasty looking 60Hz AC waveform or do you see a straight horizontal line?

4) With both MCU and oscilloscope plugged in and POWER OFF, measure the DC resistance between the probe grounding clip and a point on the MCU board which you guess is GROUND. Do you measure resistance less than 10Ω?

Answer all questions and you will be better informed on how to connect the grounding clip of the oscilloscope probe for the next step.
 

MrChips

Joined Oct 2, 2009
21,123
My scope is a Hantek 6022BE and only connects to a laptop by a usb port. I pull the AC plug on the lap top and operate with the lap top battery.
Doing that makes your oscilloscope "float".
You are now safe to connect the grounding clip to "GROUND" of your MCU board.
Connect the probe to either leg of the xtal. You will need to set the scope input to AC and about 0.2V/DIV.
Try the other leg if you do not see oscillation. What is the bandwidth of your scope?
 

Thread Starter

cstroh

Joined Jan 16, 2019
79
Thank you for that MrChips. In addition to the above description of my Hantek scope such as it is, the circuit board is powered through an isolating transformer. If I do not pull the plug on the laptop I do indeed see a nasty 60 hz and even after pulling the plug on the laptop it is still present but not as pronounced.
 

Thread Starter

cstroh

Joined Jan 16, 2019
79
The probe has two settings 1X and 10X and lists two frequencies 6 MHZ and 60 MHZ. I am not sure if the 60 goes with the X10 or the other way. The scope bandwidth is 20 MHZ. Does this bandwidth indicate it will not respond to the 40 MHZ signal? The time scale on the scope goes down to 1 ns.
 
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