Can you tell me how to test this handheld oscilloscope ?

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
Hello,
I purchased a handheld oscilloscope on amazon 2 months ago and just tried to use it yesterday.
Unfortunately, I cannot seem to get any DC waveforms from it.
I can get AC waveforms, but not DC waveforms. I realize straight DC current would be a flat line.
I can't even get that in DC mode.

Before I give up, is there a simple way to test to see if the oscilloscope is broken or if it works?
I'm not sure how to generate a DC waveform to test. Perhaps you can guide me in the right direction?

Thanks
YEAPOOK Handheld Portable Mini Digital Oscilloscope
https://www.amazon.com/gp/product/B07Z1M381W/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1

 

Delta Prime

Joined Nov 15, 2019
1,191
Hello there! :)
I purchased a handheld oscilloscope on amazon 2 months ago and just tried to use it yesterday
It should still be under warranty the easiest thing to do it's to see if you can try to return it and get a replacement. For clarification I sure you didn't blow it up yesterday!(LOL) Because if you did then we can help!
 

AlbertHall

Joined Jun 4, 2014
11,607
You need to look for 'free run' or 'auto' in the trigger menus. That should get you a straight line across the screen with nothing connected to the input. Then you select DC input coupling and connect a DC voltage voltage to the input and the line should move up for a positive voltage and down for a negative voltage. You need to set the input sensitivity appropriately for whatever input voltage you are trying to measure, just like for AC.
 

dl324

Joined Mar 30, 2015
13,527
I'm not sure how to generate a DC waveform to test. Perhaps you can guide me in the right direction?
I have that scope. When I powered it on, the default settings were correct for measuring DC signals. When I put the probe on a 5V supply, it showed 5VDC.

Make sure triggering is set to Auto. When I changed it to AC and powered the scope off and then back on, it came up with DC triggering.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
Thanks for the assist.
When I connect batteries of various voltages it does seem to reflect the correct voltage.

Now is there a simple way to generate a DC wave form to see that it correctly displays that?

Thanks again
 
DC for scopes means DIRECT COUPLED (No capacitor in the circuit)
AC for scopes means AC coupled (The constant value is removed)

DC really means DC+AC or in effect the constant value of the waveform + the time varying value.

So AC coupled on a DC source like a power supply measure the ripple.
DC measures the constant value + the time varying value.

If we had a signal A=K+B*sin(wt)

DC coupled, you would measure exactly that.
AC coupled you would measure B*sin(wt)

w is omega is known as the radian frequency and w-2*PI*f

B is the 0-peak value, so the waveform would vary +-B.As you can see the K would mess that up.

The GND position, basically allows you to see where the zero point is.

Trigger, generally has a source, a slope and the amplitude. The simplest is rising or falling slope.

The hardest part, is generally getting "something" and that's where auto-trigger is used. Auto-triger says if I don;t get a genuine trigger, trigger the scope anyway. This can lead to a wandering, non-stable trace.

So, trigger source might be internal or External.
Internal, might be set to channel A.

Real scopes have A and B and a mode where A&B are added.
It also has an obscure knob that says Invert B.
Invert B allows an A-B measurement to be performed.

A real scope its not exactly A-B; it's A-gnd-(B-gnd) which turns out to be A-B.
This measurement is called pseudo-differential. You need that third point.
The GND really is Earth and bad things happen when earth has two different potentials.

Generally, in a real scope the DUT (Device under test) would be grounded. Basically don;t use the gnd clip.
If the device is isolated, you can safely ground it when making measurements.

Don't float the grounded scope. Float the device. There should be a specification somewhere what the potential above earth the GND of the scope can be at.

Hopefully this helps.

Dual trace, dual time-base makes things MUCH worse.

Other tidbit:
A scope can have less than the specified bandwidth if no x10 or higher probe is used.
A typical scope input Z is 1M shunted by 22pf. Why?
There is a capacitor in the x10 portion of the probe.
You usually have a 1V p-p 1kHz calibrate signal available on the scope
With it in 10x or higher, adjust the cap so the edges are clean without overshoot or undershoot.
When you do that, the input Z becomes 10 Megohm resistive.

There are x100 and x500 probes. I'm not covering scopes with an input Z of 50 ohms.

The caveot means that the x1-GND-x10 probe that you choose must be within the bandwidth and compensation value, so you can screw up buying probes.

x10 means the voltage your reading is 10x higher. A measured value of 1V p-p on the scope face is 10V p-p.

I hope this helps.

Not covering active probes and ones with the x10 pin on them. It switches the scale automatically. Some Tek scopes, anyway.
 
Last edited:

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
DC for scopes means DIRECT COUPLED (No capacitor in the circuit)
AC for scopes means AC coupled (The constant value is removed)

DC really means DC+AC or in effect the constant value of the waveform + the time varying value.

So AC coupled on a DC source like a power supply measure the ripple.
DC measures the constant value + the time varying value.

If we had a signal A=K+B*sin(wt)

DC coupled, you would measure exactly that.
AC coupled you would measure B*sin(wt)

w is omega is known as the radian frequency and w-2*PI*f

B is the 0-peak value, so the waveform would vary +-B.As you can see the K would mess that up.

The GND position, basically allows you to see where the zero point is.

Trigger, generally has a source, a slope and the amplitude. The simplest is rising or falling slope.

The hardest part, is generally getting "something" and that's where auto-trigger is used. Auto-triger says if I don;t get a genuine trigger, trigger the scope anyway. This can lead to a wandering, non-stable trace.

So, trigger source might be internal or External.
Internal, might be set to channel A.

Real scopes have A and B and a mode where A&B are added.
It also has an obscure knob that says Invert B.
Invert B allows an A-B measurement to be performed.

A real scope its not exactly A-B; it's A-gnd-(B-gnd) which turns out to be A-B.
This measurement is called pseudo-differential. You need that third point.
The GND really is Earth and bad things happen when earth has two different potentials.

Generally, in a real scope the DUT (Device under test) would be grounded. Basically don;t use the gnd clip.
If the device is isolated, you can safely ground it when making measurements.

Don't float the grounded scope. Float the device. There should be a specification somewhere what the potential above earth the GND of the scope can be at.

Hopefully this helps.

Dual trace, dual time-base makes things MUCH worse.

Other tidbit:
A scope can have less than the specified bandwidth if no x10 or higher probe is used.
A typical scope input Z is 1M shunted by 22pf. Why?
There is a capacitor in the x10 portion of the probe.
You usually have a 1V p-p 1kHz calibrate signal available on the scope
With it in 10x or higher, adjust the cap so the edges are clean without overshoot or undershoot.
When you do that, the input Z becomes 10 Megohm resistive.

There are x100 and x500 probes. I'm not covering scopes with an input Z of 50 ohms.

The caveot means that the x1-GND-x10 probe that you choose must be within the bandwidth and compensation value, so you can screw up buying probes.

x10 means the voltage your reading is 10x higher. A measured value of 1V p-p on the scope face is 10V p-p.

I hope this helps.

Not covering active probes and ones with the x10 pin on them. It switches the scale automatically. Some Tek scopes, anyway.
VERY helpful information.
Thank you much !
 
OK, so the real problem is "troubleshooting" the gizmo.

#1, it's likely the FET could be damaged (shorted) without a battery connection.
#2. There are at least 2 design errors.
2a) Use a 100-240 ohm resistor in series with the gate of the FET
2b) Use 100K to 1M from the base of the FET to ground. Leakage current can turn on the FET.

Remember you get 70-80V spike.

Look at the output of your DC supply. You should have 12V DC and there should be some ripple when your AC coupled.
Watch the polarity of the adapter. Not all are center positive.

There needs to be some protection for the FET. The light bulb does part of that. You could probably use an R of 70V/0.1n Amp for testing.

There probaby is an intrinsic body diode, but you may not want to rely on it. You might want an 18V transorb or TVS diode across the S and D of the FET, so the voltage across the FET is clamped.

With just the lamp. no battery, the CD4049 Chip removed see if the 555 is generating pulses.

remove the FET and see if the input and Output pulses are there.

The FET should have a body diode in the opposite direction. It should not be shorted (measure using both polarities.

Note: A TVS diode can be unidirectional or bi-directional. Bi-directional would clamp at say +-18V. A unidirectional diode would clamp at 18V and open-ended when installed "backwards". It would go across the power supply basically or across the FET. So, a 1n5001 or a fast-recovery diode across the FET would also be better. At least 200 PIV.

The diodes are critical and should be fast recovery.

The lamp is a good thing. It's basically a current dependent resistor. At room temperature the resistance is about 15x smaller than when the lamp is glowing.
It operates similar to a Zener diode in reverse bias and can take short surges.


Rules:
The current in an inductor cannot change instantaneously.
The voltage across a capacitor cannot change instantaneously.

Good rules to remember.
v(t) of an inductor is -L di/dt.

Note: if di/dt is big, then the voltage will be BIG. di/dt is the instantaneous slope of I vs t. di/dt cannot be zero. Hence, the rule.
 
Respectfully! your KISS method.
Is far too advanced! You are simply adding confusion to the thread starter.

I think I would have been able to understand derivatives in grade school. If taught right, probably integrals too.
It sure would have made life easier.

But, then you might have to know limits. That could have helped too. At least the divide by zero thing,

i would have liked Wolfram Alpha. It cuts out the messy stuff. I got lost in the math, but if I knew conceptually what it wask, then we're good to go.

Remember that programming language lisp? or APL? or even SNOBOL or COBOL?
Infinite series - yummy. Fourier series - Yummy too. The Nyquest theorem. And now forfun, lets use imaginary numbers
let's solve the integral? I'd much like Mathmatica or www.wolframalpha.com do it.

It's nice to find out what day of the week you were born with wolframalpha.

Calendar algorithms were fun. That was phone book fun. There was always a perpetual calendar in there.
i haven't done sunrise and sunset calculations yet. Useful stuff.

Make a function that takes F(a,b) and if a=3 and b-5 produce 003005 for direct cursur addressing in BASIC.
Fun stuff.

just figured slope is easy. Instantaneous slope is a little harder.

I just don;t want to know the velocity of the fly on the propeller relative to the ground. or the proof that God exists;

The grass is green.
If the grass is green then God exists.
God exists.
QED
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
OK, so the real problem is "troubleshooting" the gizmo.

#1, it's likely the FET could be damaged (shorted) without a battery connection.
#2. There are at least 2 design errors.
2a) Use a 100-240 ohm resistor in series with the gate of the FET
2b) Use 100K to 1M from the base of the FET to ground. Leakage current can turn on the FET.

Remember you get 70-80V spike.

Look at the output of your DC supply. You should have 12V DC and there should be some ripple when your AC coupled.
Watch the polarity of the adapter. Not all are center positive.

There needs to be some protection for the FET. The light bulb does part of that. You could probably use an R of 70V/0.1n Amp for testing.

There probaby is an intrinsic body diode, but you may not want to rely on it. You might want an 18V transorb or TVS diode across the S and D of the FET, so the voltage across the FET is clamped.

With just the lamp. no battery, the CD4049 Chip removed see if the 555 is generating pulses.

remove the FET and see if the input and Output pulses are there.

The FET should have a body diode in the opposite direction. It should not be shorted (measure using both polarities.

Note: A TVS diode can be unidirectional or bi-directional. Bi-directional would clamp at say +-18V. A unidirectional diode would clamp at 18V and open-ended when installed "backwards". It would go across the power supply basically or across the FET. So, a 1n5001 or a fast-recovery diode across the FET would also be better. At least 200 PIV.

The diodes are critical and should be fast recovery.

The lamp is a good thing. It's basically a current dependent resistor. At room temperature the resistance is about 15x smaller than when the lamp is glowing.
It operates similar to a Zener diode in reverse bias and can take short surges.


Rules:
The current in an inductor cannot change instantaneously.
The voltage across a capacitor cannot change instantaneously.

Good rules to remember.
v(t) of an inductor is -L di/dt.

Note: if di/dt is big, then the voltage will be BIG. di/dt is the instantaneous slope of I vs t. di/dt cannot be zero. Hence, the rule.
AlbertHall asked.....
What do you mean by a DC waveform? DC is a fixed voltage and as such it has no waveform.
So I felt it best to give the full context.

I am grateful for your response.
Every bit of it valuable.
I'll be reading it and thinking about it for several days.....or more.

Thank you for taking the time to offer this.
I understand a good bit of it and will study it further.

Best Regards
 
Last edited:

BobTPH

Joined Jun 5, 2013
4,046
If your device under test is working, and you see no trace, the most likely explanation is that the scope is in triggered mode and the trigger level is set ouside the bounds if the waveform.

Bob
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
636
If your device under test is working, and you see no trace, the most likely explanation is that the scope is in triggered mode and the trigger level is set ouside the bounds if the waveform.

Bob
Hello Bob,

To be honest, I'm not certain that the device is working.
The device I have (shown above) has "Normal", "Single" and 'Auto" Trigger modes.
I usually set it to auto.

I still have doubts that the oscilloscope is working properly. Or maybe it has a bad probe.
That's why I was asking if someone could recommend a very simple sure fire way to see if it could or could not display a pulse signal such as the one I expected from this device I built.

I have a new set of 100MHz probes that Amazon said "Arriving Today", but now I doubt they will arrive as it's getting late and they never said "Out for Delivery". Hopefully tomorrow.
 
Tip:

  • Number of Channel:1
  • ADS2050h: 5MHz analog bandwidth @ 20MS/s sampling rate
  • ADS2031h: 30MHz analog bandwidth @ 200MS/s sampling rate
  • Max Sample Memory Depth: 40KB
  • Horizontal Sensitivity:50S / div~250S / div
  • Vertical Sensitivity: 50 mV / div~60 V / div
  • (Analog)Input Impedance:1M ohm
  • Maximum Input voltage: 40 V (1X probe), 800 V (10X probe)
  • Coupling: DC, AC
  • Trigger Modes: Auto, Normal, Single
  • Trigger Types: Rising/falling edge
Your expecting 70 V p-p. That's nearly 2x the rating with a 1x probe.
 
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