Recent Posts

1

General Technical Chat / Relay trigger when voltage above 13v

« Last post by bigjoncoop on Today at 12:07:41 am »

Trying to create a simple circuit that will trigger a relay only when the monitored voltage is above 13v.

(the output voltage of the circuit is not important. Just needs to be 0v when the monitored voltage is below 13v)



I was able to find a couple of threads on this, but there was no clear answer in the end...



I was originally thinking of using a LM386 and a TL431 as a voltage reference since I have alot of these components. But was unable to find a detailed schematic on how to do so...



Specs:

Monitored Voltage Range: 12v - 14.6v

Trigger Voltage: ≥13v

Output voltage to control relay: Not Important

2

RF, Microwave, Ham Radio / Re: fake MPF102s from AliExpress

« Last post by cosmicray on Today at 12:07:31 am »

I was searching for an SMD replacement for MPF102. The one I found that (based on specs) seems to be close, and was available at LCSC, is an OnSemi MMBFJ309LT1G. I have not yet had the time to verify their utility for this purpose.

3

EEVblog Specific / Re: EEVblog 1612 - Siglent SDS1000X HD 12 bit Oscilloscope Teardown

« Last post by EEVblog on Today at 12:06:19 am »

Hi Dave, my 1204X-HD has microphonic inputs.

Wow. Why the difference?

4

RF, Microwave, Ham Radio / Re: fake MPF102s from AliExpress

« Last post by floobydust on Today at 12:05:43 am »

Name the Aliexpress store selling junk.
JFET's I've bought there have been meh. I had to because of the semiconductor shortages, ain't nobody makin' JFETS months back.
Shenzen IC Store - they were weird looking TO-92's, laser marked, a bit dodgy made me squirm.
Fantasy Electronics CO., Ltd Store - was good. FET's I've bought there have been OK, I_DSS in spec.

5

EEVblog Specific / Re: EEVblog 1612 - Siglent SDS1000X HD 12 bit Oscilloscope Teardown

« Last post by EEVblog on Today at 12:05:06 am »

There seems to be another plastic film on the surface of the screen (?). Apparently a residue left on the surface of the screen during installation, and then the film marked with a red ribbon was put on top. Please check  it. Surface need look same half matte as SDS800. Least I have not seen this glossy surface  in SDS1000XHD what can see in your video.

Wow, you are right. less reflective now with it removed. I've never seen two films like that before.

6

Repair / Re: Tektronix DM501A repair

« Last post by David Hess on Today at 12:05:03 am »

They all have slightly different signs of trouble, but essentially nothing works well, starting with non-sensical display annunciations.

If I am reading your DSO correctly, the clock signal at pin 8 is completely wrong, and does not even meet the duty cycle requirements.

7

Projects, Designs, and Technical Stuff / Re: more modern version of tl494?

« Last post by xavier60 on Yesterday at 11:59:37 pm »

I have a strong preference for the UC3525.
It is reassuring to see in the internal block diagram, the steering flip-flop being clocked directly by the oscillator and also the latch at the comparator's output.
Not so for the TL598 despite the claims. The extra opamp might seem useful but can be difficult to achieve fast current limiting with it.
With the UC3525, I implement fast pulse-by-pulse limiting by pulling down the soft-start pin.

8

Beginners / Re: Question about use of Differential using scope USB port

« Last post by David Hess on Yesterday at 11:41:03 pm »

A differential probe *must* be grounded to the oscilloscope to control its common mode input voltage.  If it was isolated, then its common mode voltage could drift out of range and present a safety hazard itself.  So the connection to the USB port is not a concern because the probe will be grounded through the BNC connection anyway.

Manufacturers who make oscilloscopes that have galvanically isolated inputs warn about using differential probes with them unless they can be separately grounded to the oscilloscope.

9

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

« Last post by ejeffrey on Yesterday at 11:38:52 pm »

No, because I order from Digikey/Mouser/Farnell.

When there are so many cases of wrong cross sections, i would be very curious not caring about big names.

I've never measured explicitly, but if you told me you bought genuine belden wire from and authorized distributor and it was smaller than what it says on the box I'd be surprised and I would go measure some of the wires in my shop.  The fact that 5 different wires purchased from random resellers on Amazon or eBay were counterfeit it doesn't surprise me at all.

10

Test Equipment / Re: Troubles with HP-8903B

« Last post by Tony_G on Yesterday at 11:37:26 pm »

Great response SRB - Way more useful than my quick, "here is what my working one looks like" post.

Look forward to the results here.

TonyG