PCB scope - a present from Santa?

womai

Senior Member
With "does not make sense" I meant it only works for the dpscope hardware in those ranges, not that it would not be useful: The constant offset between 1:1 and 1:10 is corrected in software, which means in the more sensitive ranges it is too large and pushes the measured signal outside the measurable range. Thus no way to reconstruct the signal in those cases.
 

robimarko

New Member
Hi,i am quite a newbie in electronics but i simply love it.
Now i am looking for a cheap osciloscope cause i need it badly for ripple check and capacitor checking since i cant afford an capacitance esr meter.
How about some discount for a newbie?
 

Tealc

New Member
I just received my PCB scope and am having some trouble. Maybe someone can help.

I'm trying to pick up the eht oscillator signal from my old and not working analogue scope, which should be 30kHz, so within the range of this PCB scope. It sometimes picks up the cal signal and a 18kHz 5v signal but if I stop the signal and start it a few seconds later the software stops triggering and does no further waveform detection or display.

Every time I set up to detect the signal the software hangs and fails to pick anything up. I have to close the software and restart. Sometimes I have to unplug the USB and replug. I cannot modify the timebase without it hanging.

The USB voltage reported by the PCB scope is a little on the low side. I wonder if that might be the issue.

I've tried two windows 7 PCs. One of which should easily be capable of doing this.

I think both PCs are 64 bit, one certainly is.

I can't also find out how to calibrate the signal to zero. If I move the vertical it doesn't adjust to zero. Maybe I'm missing something, or perhaps should read the manual.

Many thanks
 

JimPerry

Senior Member
Welcome to the Forum.

Might need to start a new thread about 'scope - but I'm sure that someone will respond shortly. :confused:
 

womai

Senior Member
What horizontal timebase setting are you using to display the 30 kHz signal? The reason I am asking: One issue could be that the timebase is too slow; even then you may sometimes see something - the aliased signal; a giveaway for aliasing would be that the measured frequency (Utilities --> Measurements) is way off the true value. The scope has some noise reject built in, meaning the trigger needs to exceed the threshold for a certain minimum time before it actually triggers an acquisition. Now if your timebase is set to a very slow value and the input frequency is high, then the signal will change polarity several or may times during that "stability interval". Whether it is exceeding the threshold (again) when after the "trigger stability interval" the scope checks again can then be hit and miss - so the scope may sometimes acquire something and sometimes not.

For aliasing, user manual section 5.3 has some more details.

As for vertical calibration, yes, reading the documentation will likely help a lot :) The procedure is described in detail in the DPScope assembly manual - http://www.pdamusician.com/dpscope/files/DPScope_SE_Assembly_Guide_V1_03.pdf
 

Tealc

New Member
Thanks for your responses.

I've tried a few time bases ranging from the default down to 20uS.

Occasionally I get a waveform displayed that looks rough and this could be representative of the actual signal but any attempts to change timebase, change volts/div or interrupt the signal causes all communication with the software to fail. To recover I have to shut down the software, remove the USB, wait a bit, plug back in, wait, and then start the software. Most of the time it won't acquire anything after that either and I have to repeat.

Something is not right.

Maybe 1 time in 5 or so it will start displaying the signal and triggering normally for a bit before hanging. When it hangs button response takes 10 seconds and I can't close the software without using task manager.

It's a bit frustrating.

Just tried data logger mode and it produced a trace right up until the moment I switched my source on. I'm using a 100Mhz scope probe with the x10 switch active. Closed the software, then attached to my 1v/1kHz cal signal and the software just hangs.

My USB voltage is 4.6v, measured on a USB port with my DMM, so I wonder if this is the issue. I wonder if the PCBScope is dragging it even lower.

I've added in a powered USB hub, which is powered from a low ripple 5.04v switching power supply. In datalogging mode it'll run for a bit with no input and even sometimes continue to display a trace after switching on my analogue scope and measuring the cal signal, but if I turn the analogue scope off I can immediately hear that windows reports the PCBscope has been removed.

I'm not sure what else to do here. Is this unit defective?
 
Last edited:

womai

Senior Member
Just went down to my lab and tried it myself. My laptop runs Win 7 64 bit so similar to what you have.
Used a signal generator to produce a 30 kHz Signal, sine wave, going from 0V to 5V (i.e. 5V amplitude, 2.5V offset).

Captured it in different timebases up to max speed and down to values where I see aliasing. Started and stopped the acquisition. Turned the signal generator off and on again while capturing. Changed timebase, trigger settings, scaling etc. on the fly while capturing and while stopped. Etc etc. In no case the software hung up. At some settings the scope did not trigger (due to aliasing, or because trigger was set out of signal range), but once settings were corrected the scope resumed capture. So I don't consider a software bug a likely cause.

A few things to check in your setup:


  • is the trigger enabled (will be forced if you run at faster rates because equivalent time capture needs a trigger?). Is it set to a suitable level (within the range of the signal you want to capture)? If unsure, go to a slower timebase (where you can acquire free running without a trigger) to get an idea about the signal levels.
  • What channel are you using? Only channel 1 can be used as trigger channel.
  • Do you have ground of your circuit connected to ground on the scope? If your laptop (and thus the scope) are floating at a very different level from your circuit then connecting/disconnecting the scope could potentially mess up the USB connection, causing it to reset and thus lose connection to the scope. In that case a restart of the software (after disconnecting and reconnecting the USB cable) can be necessary. Maybe that is what's happening.
 

Tealc

New Member
Thanks.

I've tried a few setups with the ground clip.

Here's my setup.

PCBScope on breadboard, breadboard wire goes from Ch1 to centre pin on a BNC Tee, breadboard wire goes from Gnd to the outside of the BNC. Oscilloscope probe BNC is connected to BNC Tee. Probe is clipped to signal source, in this case the a transistor collector inside the EHT oscillator on a Advance Gould OS3000 oscilloscope. The ground clip is attached to the EHT box chassis, which is ground. My PC is a desktop machine but when I was using the laptop I had similar issues. I haven't tried using the laptop off battery power yet.

I've also tried leaving the ground clip off, same result, and also wiring the ground clip to the breadboard Gnd pin directly, also same result.



Am I missing something. I usually work off floating devices. Maybe it is a ground reference issue.

Maybe it is me being silly here.

I don't have trouble triggering. It's all about the USB disconnections and software hangs really.

Just tried the laptop whilst using battery and it worked well for a minute before hanging again, followed by the dreaded USB disconnection a few seconds later.
 

womai

Senior Member
Do you have a different signal source (function generator) that you could try to use to generate a similar signal (30 kHz, 5V amplitude if I unterstood correctly)? That could cut down the number of variables. One possibilty could be a Picaxe programmed to produce a 30 kHz PWM signal. At least then we bring some Picaxe connection back to this thread :=)
 

Tealc

New Member
I don't have a function gen, or a Picaxe device apart from this PCBScope.

I did manage to get this signal...



..before the USB disconnected itself. The signal is off the base of a transistor on the same oscillator circuit.

I'm scared to touch anything as the slightest thing causes USB issues.
 

womai

Senior Member
Do you have a digital multimeter? Use it to probe around in your setup to see if there are any high voltage differences present.
 

Tealc

New Member
No high voltages are being probed or measured. The EHT itself should be producing -1.5kV and 9kV but the whole reason for probing the oscillator section was to determine why I am getting no CRT display. I'm not going to be using any kind of scope to probe that section!

The only thing I can see is the Ch1 and Ch2 are around 2.4v with respect to the PCBScope's ground, which I'm guessing is what it is supposed to be so you can get negative and positive swings When I supply power to the OS3000 this jumps to around 2.9v but I'm not noticing any other spikes. There's no potential between PCBScope Ground and OS3000 ground.

It's not just the OS3000 I've had an issue with though. My 18kHz signal is a 555 PWM circuit of 5v pk-pk and this is totally ground isolated and it hangs on that too, and when I test that it is referenced to the ground of that power supply.
 

Tealc

New Member
Disconnected my probe and used a breadboard wire and was able to pick up a signal at last. It still crashes though, although it does seem to be less.
 
Last edited:
hi,

im now using to osc001 for the first time. software install ok and it all works but im unable to zoom in the the data traces. im trying to capture IR information and while its reading it as i pressed the button i cant seem to scroll back to look at the data? its on oscilloscope at 0.5m/s setting?

any help?
 

womai

Senior Member
In scope mode, the display shows the full acquired record (~200 points), so there is no horizontal scrolling. If your signal is digital (3.3V or 5V logic) you could use the logic analyzer mode instead to get a longer record (approx. 800 points).

If you want to zoom in vertically you need to adjust the gain setting and the offset slider accordingly.
 
oh thats a shame. ive been using a audio recorder via the sound card and a 1 mohm resistor. this gave me the opptunity to record and zoom in, i assume this did the same.

is there any other software that is compatable with this board?

thanks
 

MFB

Senior Member
After being initially enthusiastic about the concept of the PCBscope I rapidly became frustrated by its limitations and now rarely use it. However, its amazingly low price does mean that it can play a useful role in education, provided that the lab sessions are carefully designed around the PCBscope's capabilities.
 

The bear

Senior Member
@womai,
Brilliant bit of kit, I especially like the ability to freeze the waveforms.
My Tek 465 doesn't mind sharing.
Regards, Bear..
 

steliosm

Senior Member
Hello.
I noticed that the PCB scope os out of stock in the Picaxe store. Is there any possibility this item will be available again?
 

AllyCat

Senior Member
Hi,

Perhaps you should email the PICaxe store?

But if you need one urgently, then are you aware that the DPSope-SE is basically the same design, but enclosed in a box with optional BNC connectors (and needs some assembly). Or there is the fully-assembled II version with higher performance.

Cheers, Alan.
 
Top