bedini, the daftman SS charger & MHOP

[qtrhack]

What happens when you remove that voltage source from an inductor?   

the inductor will oppose the drop in current. 

i visualize this like a fish tank of water moving on a wagon.  when the wagon suddenly stops the water keeps moving (inertia) but can't go anywhere because the tank has stopped moving.  so then there is movement of water to the backend of the tank where again it can't go anywhere.  the water will bounce (waves) back and forth until finally settling down to zero movement.  is this a correct analogy?

i also ran a simulation here: http://www.falstad.com/circuit/e-inductkick.html

[qtrhack]

3. I have recommended that Hantek scope to people who are wanting a basic scope on a budget. For under 100 dollars you get the scope, with software that has better math capability than my old Link DSO, and cables, power supply for the scope and two reasonable probes. If I had the money I'd buy one myself.

is this what you would recommend?

http://www.sainsmart.com/hantek-pc-based-usb-digital-storage-oscilloscope-6022be-20mhz-bandwidth.html

[ayeaye]

is this what you would recommend?

http://www.sainsmart.com/hantek-pc-based-usb-digital-storage-oscilloscope-6022be-20mhz-bandwidth.html

I'm sorry but, it is said to be 20 MHz, what that means? In digital oscilloscopes it is usually considered that the bandwidth is 1/20 of the sample rate, like see the specifications of the scopes like Rigol. The sample rate of that scope is 48 Ms/s, so what do you get is a 2.4 MHz oscilloscope. Furthermore, the electronics of usb scopes is much more inferior to other oscilloscopes, it is not good at high speed.

I fully agree that using the computer's sound device for oscilloscope is a toy. Well, considering that the sampling rate is usually some 44 kHz, then the speed is 2.2 kHz, likely not very useful. But the cheap usb oscilloscopes look like toys too.

The mini crt analog oscilloscopes i talked about, they are 10 MHz and one channel. So what concerns the speed, they are much faster than the cheap usb oscilloscopes, and one can get them as cheaply. Furthermore, an analog oscilloscope is even capable of speed two times higher than its rating, thus 20 MHz in some cases. What concerns a single channel, so why cannot the external triggering be used instead? I'm not sure how well it works though, and the electronics of such cheap scopes is also sure not great.

If you can get some old analog oscilloscope cheaply, made by some good company, and when it is in a good condition, then that's great of course. Two channels and 50 Mhz, really great. If there are enough around, anywhere near where you are, some people have no hope of getting any of these. But the caveat is that they often come with faults which you are not able to repair. I think i cannot. The best is to find a good person who in essence just gives away a scope to someone who may need it, they don't sell you one with any hidden faults.

What is that speed, like one never has a 20 MHz signal. It is not about that, it is how much it shows, like fast changes, how correctly it really shows what happens. I'm sorry for talking so much, and its more like one beginner talking to the other, but i think that talking more helps to find out more.

[MarkE]

There are three factors to the bandwidth of a digital oscilloscope:

The sample rate.  The oscilloscope cannot accurately represent waveforms that have signal energy that fluctuates faster than half the sample rate.  2X sample rate / bandwidth is the ragged edge.  5X is comfortable and 10X is very comfortable.  Hantek samples at 48msps.

The analog bandwidth.  Hantek claim 20MHz for the 6022.  This would normally refer to the -3dB point of a first order low pass response.

The probe bandwidth.  A typical X1 1Megohm probe has about 10MHz -3dB bandwidth.  Even very cheap X10 probes easily do 50MHz steady state response.

Based on the sample rate and the analog bandwidth, when combined with a X10 probe, the Hantek should still have good accuracy at 10MHz.  That's pure sine waves not square waves.  It's going to be marginal looking at square waves faster than about 2 MHz. 

It is a great beginner's scope more than adequate for looking at the vast majority of non-RF circuits discussed on these boards.

Here is a listing for $50. starting bid shipped two channel analog 100MHz scope.  It is also a twenty five year old machine.  http://www.ebay.com/itm/Tektronix-Oscilloscope-2235-100MHz-/371183147172?pt=BI_Oscilloscopes&hash=item566c3d58a4

[ayeaye]

I look at this usb scope, and even if it can be used, no way can i love it.