Simple oscilloscope for Picaxe work - finally finished! (DPScope SE)

[John West]

A suggestion for folks who have the SE scope and find the offset null adjustment to be quite sensitive. Try putting a 10 to 50 Ohm resistor across each trim pot to reduce the sensitivity. As long as the null point is still within the adjustment range of the pot, the lower the resistor value chosen, the better for ease of adjustment.

For the the price of adding 2 resistors to the circuit this should solve the sensitivity problem without the need of an unreasonably low value trim pot, while still maintaining a low impedance reference point.

 

[BCJKiwi]

Thanks for testing (my suggestion @ post #93). I did not get around to checking it myself so good to see a positive result to my musings.

 

[smeagol]

I just asked Womai, via e-mail as i had forgotton my login details and am away from home, about the possibility of seeing samples prior to trigger ( he responded that it is notreally possible with the SE )

Now a supplimental question

How does the SE handle the trigger. Does the pc program send the trigger value to the SE hardware and then the SE hardware send the samples to the pc software?

How long is the delay between the trigger and the samples beibg sent.

The questions are just out of curiosity really.

 

[womai]

The PC software tells the scope which trigger threshold, trigger polarity, and trigger source (e.g. CH1) to use. If the acquisition is to be triggered (source CH1 or ext. trigger) then the scope waits until the signal into the trigger channel crosses the threshold. This causes a comparator interrupt, and the scope now acquires a full record. The PC software constantly polls the scope, i.e. asks if acquisition has finished. If that is the case then the PC asks the scope to send back the acquired data. The scope always reacts to commands by the PC, it never initiates any data transfer (apart from replies to a command/request from the PC).

Have a read of the hardware description (fro the website under "Downloads"), this goes into some detail about the trigger.

The delay between trigger event and capture start is one sample period (this is necessary to make sure the trigger is valid and not just caused by noise), thus depends on the currently selected sample speed. The delay between end of the acquisition and start of the data transfer is not perfectly predictable (the USB link does not have any guaranteed latency) but if there is no other traffic on the USB bus then it is around 1 ms. Transferring a full two-channel data record takes about 10 ms.

 

[smeagol]

Thanks for the info, detailed as usual

 

[womai]

After several reports complaining about the readability of the DPScope website I discovered that while it displayed fine in IE and Firefox (both of which I had used to verify my design), most of the pages were lacking the white background when viewed in Google Chrome (which I usually don't use). Not good. I finally got around to fixing the behavior - at least I hope so (now looks fine on my computer). Please let me know in case you still encounter any problems.

 

[smeagol]

The overview page for the SE is just showing as a blank white panel. I'm sure there was information on that page before.

 

[womai]

Ooops, too much of a good thing - first text with no background, now background with no text Thanks for the feedback - fixed it now.