Recent Posts

1

Repair / Re: Motherboard has no power - Clevo W650SC

« Last post by modoran on Today at 10:51:38 pm »

Then use IPA to see what is getting hot. Is not as fast as a thermal camera, but it will din the job.

Inject 1V and a lot of amps into the circuit.

2

RF, Microwave, Ham Radio / Re: RF Test Automation

« Last post by vino on Today at 10:47:57 pm »

These are the parameters that I'm interested in automated testing.
1. Gain
2. Gain Flatness
3. IMD
4. Psat
5.P1dB
6. Spurious

I know how to test them manually and I'm also confident in using the equipment and tools to test them.
I just want to take advantage of capability of the programming language such as Python to make my work easier. By incorporating test automation.

3

Beginners / 555 driver and Transformer questions

« Last post by DanMann on Today at 10:47:40 pm »

I apologize if this is the wrong section, I am having trouble searching for answers as I think I am unable use the correct words to explain for a search query..


Do the traditional transformers need to work at specific frequencies? A hypothetical, I have a radio shack transformer on my bench that is primary 120V 60Hz with an output of 12.6- 0 -12.6.
If I put a lower frequency the transformer gets noisy, which seems like trouble. However would running say 180Hz to about 1KHz have any ill effect on the transformer.?

In trying to make a 555 astable driver to a mosfet to cycle a (different)  transformer at 180Hz from a 6 volt battery.
In using online calculators  I have been playing with combinations of resistors and capacitor and see that I can get 180Hz in many ways, but the time high and time low vary.

Is there a ideal combination ratio of the high and low time?

4

Projects, Designs, and Technical Stuff / Re: "practically smallest" debug connector on tiny pcb

« Last post by Wilson__ on Today at 10:46:18 pm »

Many thanks.  Very clever way to do it.  Castellated board edge takes little space on pcb

5

Projects, Designs, and Technical Stuff / Re: Webench Help - 5V buck mode supply

« Last post by davegravy on Today at 10:43:42 pm »

I don't see a RT pin in the datasheet : https://www.ti.com/lit/ds/symlink/lm64460-q1.pdf

It turns out digikey links to the wrong datasheet (the LM63460) which is different by 1 digit

But I really have to wonder why you'd decide to make a 5v 0.7A dc-dc converter with a chip that costs 5$ in small quantities. It's a chip designed for up to 36v, with up to 6A switching current, not for circuits which are meant to output less than 1A of current.

Fair question. It's mainly because $5 is nothing in this context.  This would be low volume production where the cost of operating the devices over 10+ years is going to overwhelm the parts, manufacturing and (TBD) even cost. These are remote devices that'll be costly to do battery service on, and which have to be compact and can't do much energy harvesting, so a few percent power savings is significant.  This was top of the pack out of Webench.

But maybe I'm underestimating the design effort and one of your (much appreciated) suggestions will be better.

6

Microcontrollers / Re: A couple questions about Milk-V Duo boards

« Last post by SiliconWizard on Today at 10:27:21 pm »

Thanks! So, in terms of pure performance, at least from your benchmark, the C906 looks way behind a Cortex-M7 at the same clock freq, but not too far between a M7 @600MHz and C906@1GHz.

In terms of power draw, the "missing" info is whether it has any kind of sleep mode, which you can go to and resume from, either when running Linux, or baremetal.
62mA on "idle" is not bad for a CPU @1GHz, but the ability to put it in some standby mode drawing much less, and from which it could get out of within maybe less than 1s, would be nice. I haven't found the info so far and may have to order boards and figure it out myself.

7

Test Equipment / Re: Old Fluke Multimeters

« Last post by Dave Wise on Today at 10:26:05 pm »

I finished my 8060A beep frequency mod.  Works great.  See topic "Low Frequency Continuity Beep for Fluke 8060A".

8

Projects, Designs, and Technical Stuff / Re: Nichicon UPJ for switching power supplies - what's so special about these caps?

« Last post by mightyohm on Today at 10:25:43 pm »

I was curious if there was a specific characteristic of the UPJ that made it particularly suitable for switching power supplies, and whether that would imply a tradeoff to using the same caps in other applications. It sounds like it may be just marketing. Would love to hear from someone at Nichicon regarding this but they have ignored my request.

Regarding stability, it sounds like it is not a concern in this particular case.

9

Projects, Designs, and Technical Stuff / MAX6399 - Undervoltage Lockout Not Working

« Last post by waymond91 on Today at 10:25:19 pm »

I have a circuit using the MAX6399 acting as an over-voltage and under-voltage lockout.
Here is a link to the part: https://www.digikey.com/en/htmldatasheets/production/2916090/0/0/1/max6399
I had one small hiccup where I got the gate pin wrong on the pcb, but I have bodged a to-220 onto the pads.

I was targetting an overvoltage lockout at 14.4V, and undervoltage at 11.6V. However, the overvoltage kicks in near 13.7V, and the undervoltage never fires.

I can measure the "OUT" and "OUT_SET" threshold voltages as I adjust the supply and see they are near their respective thresholds at the appropriate voltage.
For example, the undervoltage is near 0.5V at 11.6V, and the overvoltage is near 1.23V at about 14.4V

We had this behaviour after replacing the mosfet but before replacing the MAX6399. I have since replaced the max6399 and get the same behavior.

The Schematic


3D Board


Board with bodge mosfet AKA "The Bodgefet"

10

Projects, Designs, and Technical Stuff / Re: Powering NeoPixels from 3.3V - Wrong but everyone does it?

« Last post by thm_w on Today at 10:25:05 pm »

Ignore the first response above.
We are not talking about logic levels, OP is talking about supply voltage specifically.

WS2812 just has a recommended range of 4.5 to 5.5V, no specified value I see. Blue Vf = 3.2 to 3.4V
WS2812B datasheet mentions 3.5 to 5.3V, but then later gives a recommended value of 4.5 to 5.5V. Blue/Green Vf = 3.0 to 3.4V
SK6812 mentions 4.5V, 5V, and 5.2V without giving a specific minimum. Blue/Green Vf is stated as 3.0 to 3.3V.

So no, you can't reliably have any of these working at 3.3V Vdd because the Vf of the LED could also be 3.3V or higher (as langwadt mentioned). You might get a bit of light but not the specified amount.

So my question is, can NeoPixel 3.3V operation be verified analytically, such that a design engineer can take an informed risk?

For example, perhaps it is known that the logic is 3.3V compatible CMOS but the LED Vf is 3.5V which would mean reliable operation at 3.3V but with compromised brightness / colour mixing.

If you don't care about brightness meeting spec then use SK6812 or something with a low Vf as possible.
But then whats the point of having a design without consistent brightness?