Recent Posts

1

Power/Renewable Energy/EV's / Re: Such a horrible design from Lenovo

« Last post by jonpaul on Today at 05:42:29 am »

Lenovo Thinkpad Carbon X1 running for many years in continuous use.

No issus on PSU or cooling.

Just my experience

j

2

General Technical Chat / Re: Fun for nerds

« Last post by RoGeorge on Today at 05:39:36 am »

This Is A New Rocket - Smarter Every Day 297
SmarterEveryDay



 

3

Power/Renewable Energy/EV's / Re: 5 out of 6 vendors are scamming people with wrong crosssection of cables

« Last post by jonpaul on Today at 05:35:26 am »

We use only genuine Belden wire and cable as our work is important

The Chines commi junk eg eBay, Ali express is penny wise and pound foolish.

Try a magnet on the ChiCom wire to detect the iron.

Return for refund all the junk

Jon

4

Repair / Re: Mig welder wire feeder controller board not working

« Last post by TERRA Operative on Today at 05:28:05 am »

Just the electrolytic capacitors, film and ceramic capacitors very rarely go bad.

5

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by nctnico on Today at 05:27:39 am »

If you look carefully at the 450MHz screenshot Performa01 posted, you'll see that the displayed signal can't be right. Just look how the histogram for the frequency measurement shows a wide spread instead of a single frequency! And also look at the amplitude compared to the 408MHz signal. IOW, the screenshot doesn't show what is actually happening. Just stick to testing fs / 2.5 + 2% or so. DSOs can show fantasy signals in such circumstances!

I also have the feeling that the interpolation already suffers a bit in the 450 MHz screenshot.

The 450MHz signal in the 450MHz screenshot definitely is a fantasy signal. The amplitude suddenly gets higher (compared to the 408MHz screenshot) while you'd expect it to be lower. I don't know what the signal amplitude is at the input but likely it is quite high to at least see some signal. When increasing the sensitivity, there will be more gain so likely the front-end is now distorting due to clipping / overdrive recovery / etc. When low-pass filtering the distorted signal from the front-end you still get a sine wave but it has nothing to do with whatever sine wave signal is at the input. And there may be other elements in the signal processing chain as well. I've seen similar behaviour when testing the R&S RTM3004 under similar conditions.

When doing these tests, you need to start with setting the oscilloscope to a v/div setting which does not distort / clip the input signal in the analog front-end and use that v/div setting as the lower limit you can set the sensitivity to. That way you ensure you are always looking at a real signal (if you can see any).

6

Buy/Sell/Wanted / Re: FS (EU/US) PHV 1000 100:1 400MHz High Voltage Oscilloscope Probe

« Last post by jonpaul on Today at 05:26:23 am »

We had bad experience with the PHV 100x probes, off attachemebt of tips and leads, flimsy construction, defective delicate comp box trim.

We suggest only Tektronix P6013, P6015 P6015A for any serious use.

j

7

General Technical Chat / Re: Relay trigger when voltage above 13v

« Last post by AVGresponding on Today at 05:26:19 am »

The LM386 is an audio amplifier IC. I think you meant the LM393.

Plenty of good ideas have been given above. If you want an off the shelf solution, then you could use a voltage monitoring relay.

The LM386 is basically a power op-amp, and would be fine to use for this, though the quiescent current might not be optimal. It'll certainly be better used as this than as an audio amplifier; it's horrible at that

I don't think so. I would be difficult to use the LM386 as a comparator. The input voltage is limited to +/-0.4V, it's internally biased, so its output sits at half the supply voltage and the DC gain is only 20. No doubt it can be hacked into a comparator circuit, but it's much easier to just use the LM393.
https://www.ti.com/lit/ds/symlink/lm386.pdf

TL431, driving the base of a PNP transistor to switch the supply to the relay.  You'll need appropriate base resistors, an anti-parallel diode across the relay coil, and possibly a high value feedback resistor from the collector of the PNP to the TL431 REF pin to add a little hysteresis.  Make the feedback resistor much lower, and once triggered it will latch on, till you momentarily either remove the supply, or ground the REF pin.

Like this.
[ Attachment Invalid Or Does Not Exist ]

The OP mentioned wanting to use an LM386 because they have lots of them. I always try to answer the question being asked, and not ignore it.

The output biasing is trivially easy to incorporate as part of the design. The input limitations require more thought, the voltage divider values can't be as arbitrary as you could normally get away with. Aside from that, it's perfectly feasible, if not optimal.

8

Test Equipment / Re: Rigol DHO800/900 Oscilloscope Bug Reports + Firmware

« Last post by csuhi17 on Today at 05:21:37 am »

I am not exactly sure what you're seeing. 

I've been seeing this on the display for almost an hour.
Then I'll wait with him to see if it revives you.

9

Beginners / Re: 555 driver and Transformer questions

« Last post by Andy Chee on Today at 05:18:20 am »

@Andy, the problem is the vibrators have a limited life span and have not been available in a very long time. This is due to better vibrator/transformer configurations.
I did run one with a vibrator and got two pictures of settings at different time intervals. Notice how the frequency changes. I think this may be due to how this cheap oscilloscope takes the readings. I did read the frequency on my multimeter and in the range of 200hz even though the scope said otherwise.

Ok, so just to confirm.  Everything completely original as possible, but you're more than willing to ditch the vibrator unit?

My suggestion was to use the vibrator (with appropriately serviced and cleaned contact points) to drive the MOSFET/transistor/IGBT/whatever. 

Due to the MUCH lower current involved and no voltage spikes, the contact points would last infinitely longer if used solely for driving a MOSFET/transistor/IGBT.

From what little knowledge I have about these things, vibrators predominantly fail from contact arc burning, so this approach of driving an external semiconductor with the vibrator should be a viable one.

But if you're willing to sacrifice originality and ditch the vibrator, that's ok too! 

Are you able to at least get your existing vibrator working electrically (i.e. clean the contacts), and hook it up to the oscilloscope disconnected from the HV module?  This should give you a starting point for duty cycle, then you can adjust the 555 to match duty cycle.

10

Test Equipment / Re: Magnova oscilloscope

« Last post by core on Today at 05:16:58 am »

I wonder why they announced this oscilloscope, but after almost a month there was no news.
Maybe they just wanted to see how interested users would be. But this method might backfire on them, as it creates unrealistic expectations. Does that "Damn Good Software" exist?
It seems that nowadays rushing might become a habit.

On the other hand, Rigol came out with the new series all of a sudden, in a total surprise. What we know for sure with them is that we are subsequently left with what we originally got. Very little chance of major improvements in firmware.