Previously to these last two posts I used the laptop on mains power and had problems with the PD software where the software would complete a starter cranking/charging test on its own. These last two posts using the laptop on battery didn't seem to produce a problem. The Mini PC seems to create noise, I'm not convinced it is the mains supply, but could be the quality of the PC as Kev has pointed out previously during his 'Horse Shoe Repairs'
I'm going to start unplugging leads from the PC to see if the noise disappears, probably unlikely as there is not much plugged into the PC except the touchscreen monitor and the wireless mouse, along with a remote powered USB drive!
Mike my mate the computer guy advised yesterday something I had not thought of, that being that the touch screen monitor has a direct 240 V AC power supply and the Mini PC is directly mounted at the rear of the monitor. This evening I am going to try and move the PC away from the monitor and see what changes. I'll let you know.
I've stayed back this evening at work and tried some experiments with the Mini PC. I have tried moving it away from the monitor and its power supply, made no difference. I disconnected the additional powered USB hub and that also made no difference. I disconnected everything and just left the monitor, scope, mouse attached, tried using both scopes and each scope failed, noise and high rippled voltages from both. The PC's mains power supply has an output of [5 V 4 A], I can't see that causing the noise issues. I must conclude then that having disconnected everything and noise still present that the Mini PC itself must be the cause.
So, looking at the Mini PC technical specifications (on paper) with the additional 120 GB drive fitted, comparing these specifications to the Pico data I have, I have exceeded the recommendations Pico advise, so I have to put the noise down to the build quality of the PC not being adequate, hence I need a recommendation for a PC that is suitable for use with PicoScopes.
You mentioned that you cannot see the Mini PC power supply being the source of the noise.
I believe it can be and in this case, most probably is the source (Not the Mini PC)
Unfortunately this is something we cannot disconnect as we lose power to the PC and so power to the scope etc.
We could try "Sniffing" for the source of the noise using your scope powered by the laptop (on laptop battery)
Here you can connect a test lead to Channel A of your scope, set channel A to +- 50 mV, connect the ground lead of the test lead to chassis ground and maneuver the free end of the test lead signal wire around the Mini PC power supply/transformer, power lead 240 V (if applicable) and 5 V lead post transformer.
Very similar in fashion to using the COP Probe when sniffing for HT "field" leakage
You will be looking for a repeat of the high frequency noise we saw in your previous scope capture, where ideally the greater the amplitude, the closer you are to the source of the noise.
This is assuming the noise is emanating external and can be detected with our test lead.
Basically what I am trying to say here is this may or may not work to help you locate the source of the noise.
I didn't think 5V @ 4A would cause the issues, however I think I see where you are coming from, the transformer that plugs into the mains, this is where the AC to DC rectification will take place and suppose any smoothing of the supply will also take place. I'll pop across to the electronics shop across the road tomorrow and have a word with the lady in there, I'll let you know what she thinks!
I dont believe your source is classic, just diodes and transformer but rather its a switched power supply, using high frequency controlled mosfets. This is where your noise might come including at the 5V level, as there is not much galvanic isolation either.
Just buy a proper laptop.
liviu2004 wrote:I dont believe your source is classic, just diodes and transformer but rather its a switched power supply, using high frequency controlled mosfets. This is where your noise might come including at the 5V level, as there is not much galvanic isolation either.
Just buy a proper laptop.
Once again thank you for your valuable support. I bought a new power supply with built in smoothing circuits. I hope I'm not speaking too soon, but I have done several BD tests and the ripple is in the 'green' every time to date.
I have done the AC and DC tests along with current, please see what you think.