Recent Posts

11

PCB/EDA/CAD / Re: JLCPCB alters soldermask without any notice

« Last post by thm_w on Today at 08:20:38 pm »

Photo would help.

I'm surprised they bother to look at any gerbers that don't obviously violate the rules. It seems like a waste of time to me.
Just have the disclaimer "we make your design if your design is bad no refunds."

12

Microcontrollers / Re: Dim OLED Screen replacement for Agilent Keysight U1253A U1253B U1273A U1273AX

« Last post by Tarloth on Today at 08:16:45 pm »

Thanks Again! I did try today to buy in my country the OLED display and none it's compatible, I need to buy in ebay or in aliexpress then would took one month to arrive.

I can make the IR-USB cable meanwhile , I have several CNC machibes to make the head, I can post results here.

Anybody  used another colour than Yellow for the display? It's less readable in white than yellow? 

Thanks again for your enormous work, it's a real shame that Keysight not provided this firmware mod.

13

Beginners / Re: Put LC filter before or after LDO?

« Last post by AnalogTodd on Today at 08:12:27 pm »

What nobody has addressed yet is a major concern: regulator stability. A capacitor is needed on the output of almost every linear regulator to provide a pole for stability. For a regulator like this, the pole is formed by R_L*C_OUT.

When you add an LC on the output you create a double pole at the LC resonant frequency. If this happens to be before the unity gain frequency of the regulator, you get a 180 degree phase shift while you still have gain, leading to oscillation.

So essentially, it's generally a bad idea to place a LC filter after an LDO, unless you measure and check for oscillations?

Absolutely. I've had far too many people contact me before for an application where they aren't getting the right output voltage. I have them hang a scope probe on the output and it is oscillating and once I get to look at the schematic I see an LC filter with a resonant frequency well inside the regulator bandwidth. Pull that off and everything is happy.

Push the frequency high enough it is outside the loop bandwidth and it will work as well.

14

General Technical Chat / Re: new propellantless drive company

« Last post by tom66 on Today at 08:10:43 pm »

I had a quick look at the patent, and frankly the patent clerk AlbertE would laugh.
In the patent they state the stuff works in an enclosed system. So you have got something generatig a force inside a closed box and it should propell somewhere? That is against the fundamental laws of physics, imho.
They should apply for the Nobel prize as well..

All propellantless drives violent fundamental physics laws (if they are to operate in space).

There are two possibilites:
- 100+ years of physics understanding is in error somehow with an effect not yet studied or understood allowing a propellantless drive to function
- They don't actually work

So far no one has made a true propellantless drive function in true space environments.  They have only shown some effect when tested in a lab, but so far this effect has been accounted for as a magnetic bias, thermal air currents, or an experimental error.

Perhaps it is possible, but I have my doubts.

15

Microcontrollers / Re: Attiny1606 burning out when connected to a drv8251

« Last post by lavaman on Today at 08:08:33 pm »

It might be some kind of a problem with the reference voltage, but i don't think that's the case because that would result in neither of the inputs working

16

Projects, Designs, and Technical Stuff / Re: Looking for a sensor to detect burning "smell" of coal and wood

« Last post by Sal Ammoniac on Today at 08:08:04 pm »

A VOC (volatile organic compounds) sensor might work.

17

Beginners / Re: buying a oscilloscoop

« Last post by baldurn on Today at 08:05:45 pm »

i dont understand why i need a more expensive scope ? can you guys explain to me in a simple way thanks
iam not a expert like you guys i dont design pcbs and i never wil ,i do basic stuff like installing rgb mods ,looking at schematics fixing crt tvs and monitors
old computers like commodore and pcs and some videogame console repairs

not shure why i need a 4 channel scope that cost 500 euros or more

also about waranty i think with have 2 years waranty in the netherlands by law

Going by "need" based on what you have described, you could get an old analog scope for €50 on your local equivalent to ebay. It might not be a bad choice leaving you with more to spend on other things, like a high voltage differential probe.

But since you stated a budget of €300 that is close to some very nice options at €400. It is not that you _need_ those nice scopes, but like a nice car compared to a very budget car, it is simply much more enjoyable to work with. You get the very latest in user interface with touch screen and user-friendliness.

The €50 used analog scope with two channels might solve the task equally well, but it is heavy and clunky, taking up most of your desk. It might require you learn how to use a special trigger input as a third channel and learn other tricks. Compared to the new generation Siglent and Rigol of which the later can run from an USB battery bank and is very lightweight. Four channels vs two similarly a matter of a very slight price difference, so it might be stupid to forgo the extra channels for the day, where you are stuck needing them.

The €300 options you found just don't have a very good reputation here, as you might have discovered.

Plenty of people swear that the old analogs are the best, and the old computers were build with those. Personally I am all digital, but in my opinion if you won't afford the €400 options, you might as well go all in on getting the job done with the old tech.

18

Microcontrollers / Re: Attiny1606 burning out when connected to a drv8251

« Last post by lavaman on Today at 08:05:33 pm »

I added those resistors just to be sure not to damage the attiny, but i have tried it even without them resulting in the same situation. One of the inputs can be fully controlled and the other is for some reason always low. Even tried if the attiny pin works, it does.

19

Microcontrollers / Re: Attiny1606 burning out when connected to a drv8251

« Last post by MarkF on Today at 08:02:31 pm »

Why do you think you need to have resistors between the Attiny and the DRV8251?

They are both powered by 3.3V?

As far as the built-in pull-down resistors.  From what I see the pull-downs are 100KΩ (Figure 8-6).
Negligible to the Attiny.  They are only there so the motor outputs are at Hi-Z (disabled) if the
inputs are not connected.

Also, insure that both Attiny pins are configured as outputs.

20

Test Equipment / Re: DMM Input Capacitance

« Last post by alm on Today at 08:01:22 pm »

It makes sense that on a guarded multimeter (which I'd expect any halfway-decent bench meter to be), the impedance of the low terminal to ground is much lower than the high terminal. Generally the guard is connected to the low terminal except on meters with a separate guard terminal where you generally want to connect guard to the low terminal unless you are connecting it separately. And the guard is a big box (or at least a trace) between the input circuit and ground. So it should have a lower impedance to ground to do its job of shunting common mode current away to ground. In terms of impedance to ground or noise, you should treat your DMM a bit like a scope in that you connect the high lead to the high impedance point of the circuit and the low terminal to a low impedance point of the circuit. Connecting the low terminal to a high impedance point (like a high-impedance voltage divider) can lead to increased noise and unexpected circuit loading.

SDM3055X-E:
DCV:
Negative Terminal: 1.47615pF
Positive Terminal: 0.55323pF
...

These figures look off by at least two orders of magnitude. Figures like this would be good for an active FET scope probe, and unthinkable for a DMM. It may be either that the ground-referenced LCR meter was shorting it to ground, or maybe there was no connection between the Allen key and the DMM's ground.