Hello everyone,
I needed a 4 MHz clock from Arduino Uno with 5 V pulse amplitude. I have used the guidelines given by https://www.reddit.com/r/arduino/comments/3898g6/generating_14_mhz_clock_on_arduino/.
I can see the clock working with oscilloscope, but the amplitude is 3.3V not 5 V as usual from digital output.
Is there a simple explanation for this?
Is there a simple explanation for this?
Yes, but you did not provide enough information for anyone to guess what it might be.
Is the oscilloscope properly calibrated?
How is your Arduino UNO powered? What does the oscilloscope say about the voltage at the +5V pin?
Don't forget that output pins have some internal impedance (~25-50ohm).
If you "load" the pin with e.g. a 100ohm resistor, those two resistors form a voltage divider.
100ohm is just an example, and too low for a pin.
Leo..
What is your scope, if the bandwidth is not about 3 to 10 times the maximum frequency you are looking at then it will look low.
Thank you everyone for your fast responses.
jremington:
Yes, but you did not provide enough information for anyone to guess what it might be.Is the oscilloscope properly calibrated?
Grumpy_Mike:
What is your scope, if the bandwidth is not about 3 to 10 times the maximum frequency you are looking at then it will look low.
Yes, it is properly calibrated. I am using Tektronix TDS 3032 300 MHz oscilloscope and monitoring 5 MHz clock pulses.
johnwasser:
How is your Arduino UNO powered? What does the oscilloscope say about the voltage at the +5V pin?
I power my Arduino UNO through USB, oscilloscope says that the +5V pin is at +5V, so it seems to be ok.
Wawa:
Don't forget that output pins have some internal impedance (~25-50ohm).
If you "load" the pin with e.g. a 100ohm resistor, those two resistors form a voltage divider.
100ohm is just an example, and too low for a pin.
Leo..
I am using the AC coupling while monitoring the clock output and 50 Ohm input impedance. So maybe that is a reason for not seeing 5V,my 50 Ohm input has too low resistance compared to the pin?
If I use 1 MOhm input impedance, my clock pulses look not rectangular and I still do not get 5 V, is that because of the high RC constant while using 1 MOhm input impedance?
If these points are correct, what is the best way of monitoring pulses of such frequency?
ignas1:
I am using ... 50 Ohm input impedance. So maybe that is a reason for not seeing 5V, my 50 Ohm input has too low resistance compared to the pin?
Well, since as explained above, the Arduino has an output impedance of some 35 Ohms, the loading it with 50 Ohms would explain that perfectly.
ignas1:
If I use 1 MOhm input impedance, my clock pulses look not rectangular and I still do not get 5 V, is that because of the high RC constant while using 1 MOhm input impedance?
Well, yes and no, it is in fact because you are not using a properly compensated probe.
ignas1:
I am using the AC coupling while monitoring the clock output
You should probably use DC coupling to monitor a pulsed DC voltage.