OSC001 DPScope DC offset


I have just installed the scope but seem to have some DC offsets. With CH1 shorted to the adjacent ground pin I get 392mV DC and with CH2 shorted 598mV. (open circuit , just the bare board nothing connected except the USB lead CH1 is 2.32V and CH2 1.97V).

The schematic shows adjustable R12 and R13 labelled as offsets and I have found these on the board. Is it okay to adjust these or do they do something else ?


Senior Member

Because the PCB/DPScope has only a single (USB) Positive supply (i.e. no negative rail) it is "unusual" (for a 'scope) that it is intended to indicate a voltage of around 2 - 3 volts when NOT connected to anything (i.e. "open circuit"). So yes, you are correct that the input(s) should be connected to Ground before making an Offset Adjustment (assuming that you intend to measure signals with a reasonably low source impedance, typically <10 kohms).

Yes, AFAIK it is OK to adjust those named pots, but before you do, check that the (USB) supply voltage is within the specified range (normally 4.5 to 5.5 volts). The DPScope software has a function to test this: "Utilities : Check USB Supply". And there may always be some "drift", so don't expect to get to (or remain at) zero, to the nearest milliVolt (or on all ranges at the same time). ;)

Cheers, Alan.


Hi Alan,
The USB voltage was 5.03V and with some adjustments both channels are now just a few mV (both under 10 mV with inputs grounded on the 0.5V/div scale) so thats got that fixed.

I seemed to have a lot of noise with the top to bottom spikes with a vertical sensitivity of 0.1V/div or less and a Hz timebase of 0.5ms/div but these were all on the left hand side of the screen most in the first 20% or so. Eventually I found that turning off the waveform measurements display fixed the problem.

I only plan to use the scope on standard Picaxe projects and it looks to be a good learning tool for that. if the probe reading when disconnected bothers me then I could always try the effect of a resistor across the probe and ground !

Thanks for your help


Hi Wolfgang,
Thanks for the link thats really helpful as is the other information that it leads to. I am gradually getting used to the scope and its amazingly good. I wasnt expecting anything so comprehensive . The logic analyzer has been very useful as I experiment with a bipolar stepper motor. A fascinating bit of technology at an incredibly low price. Very impressive design. Thanks for all your work on this.