Search found 78 matches

by davef
Fri Oct 09, 2015 7:22 am
Forum: DSO138
Topic: 9V power adapter issues
Replies: 12
Views: 21487

Re: 9V power adapter issues

Your picture of the test signal looks OK.

I would have expected you to just pick up 50/60Hz with your finger on the probe. Try the finger-test with a 9V battery.

If you connect the probe centre to probe ground with the power supply does the rubbish disappear?

Thanks for the link.
by davef
Wed Oct 07, 2015 7:27 pm
Forum: DSO138
Topic: 9V power adapter issues
Replies: 12
Views: 21487

Re: 9V power adapter issues

According to the schematic there seems to be adequate filtering on the supply input. Or that must be a pretty noisy power adapter. Is the noise getting into the signal path? Anything change if you move the leads and/or 'scope around?

Could you link to your enclosure files?
by davef
Wed Oct 07, 2015 7:20 pm
Forum: DSO138
Topic: Troubleshooting Internal resistance
Replies: 4
Views: 6715

Re: Troubleshooting Internal resistance

Is it a real sawtooth or just slow ramp-up and ramp-down times?

Post picture.

What is the frequency of the sawtooth waveform?
by davef
Fri Sep 25, 2015 7:42 pm
Forum: DSO138
Topic: Nowave, but all is working.
Replies: 7
Views: 9045

Re: Nowave, but all is working.

With a DC voltage, say a 1.5V battery, on the input and DC coupling and did you actually look for a DC voltage on the ADC pin on the uP? Try different gain switch positions and see if anything shows up.

Firmwave version?
by davef
Wed Sep 09, 2015 1:40 am
Forum: DSO138
Topic: US AC outlet
Replies: 4
Views: 6997

Re: US AC outlet

More than adequate. You would need a special setup to measure AC current. I did test the max usable frequency for a sine wave and for getting a reasonable square wave. From memory the square wave frequency was about 10kHz. I used my unit to check out a pure sinewave inverter, it is probably OK for t...
by davef
Tue Sep 08, 2015 10:09 am
Forum: DSO138
Topic: US AC outlet
Replies: 4
Views: 6997

Re: US AC outlet

120V * 1.414 * 2 = 340V peak to peak.

DSO138 max input 100Volts peak to peak, but I it will only display 40Volts peak to peak. Looks like a 10:1 probe would just do it.

Because you had to ask this question I must add ... be careful actually doing the measurement!
by davef
Thu Aug 27, 2015 8:50 am
Forum: DSO138
Topic: Probe question
Replies: 5
Views: 9247

Re: Probe question

I think I saw the term bandwidth. I believe bandwidth would be to the -3dB down point. For use on the DSO138 you will never see the difference, if there is one. Maybe, the 60MHz probes are cheaper because they are more popular. According to the link there could be other parameters that could make on...
by davef
Mon Aug 24, 2015 7:38 pm
Forum: DSO138
Topic: Upgade dso 138 without updating firmwares
Replies: 2
Views: 5740

Re: Upgade dso 138 without updating firmwares

Seems you have chosen a different disc capacitor (C18?) to lift up and connect to analogue ground. The original mod was to lift the ground leg of C15.

Did you try the original modification?
by davef
Mon Aug 24, 2015 7:22 pm
Forum: DSO138
Topic: Probe question
Replies: 5
Views: 9247

Re: Probe question

Why would a person buy a 20MHz if the 60Mhz cost the same?
Better quality, compensation built into the probe, 1x, 10x, ref positions on the barrel, other specifications.

Do they actually give a 3dB down frequency or some other idea of the frequency response?