Recent Posts

1

General Technical Chat / Re: Powering an LED from international line voltage

« Last post by NiHaoMike on Today at 01:43:53 am »

How about use multiple smaller LEDs in series? Then you'll need less current for the same brightness, possibly to the point where a series resistor would become practical.

2

Beginners / Re: 5V buck converter debugging

« Last post by davegravy on Today at 01:42:50 am »

I would suggest trying again. Bring it up to 4 volts and check some waveforms, I am hopeful with that information you will find the issue and be up and running 

I don't have a great scope but these were all taken with my 10X probe. Does this suggest there's insufficient input filtering?

Vin at 3.6V RMS


Vin at 3.7V RMS (where the IC starts drawing current)


SW1/2/3 (Vin=3.7V RMS)


Vout (Vin=3.7V RMS)


Cboot (Vin=3.7V RMS)


SW4 (Vin=3.7V RMS)

3

Beginners / Re: AC brushed motor, caps & inductors

« Last post by amyk on Today at 01:34:24 am »

Check the mica between the commutator bars. With long-term wear they can start to protrude a little and cause additional arcing and interference.

4

Projects, Designs, and Technical Stuff / Re: Duty cycle and frequency to drive LED for best energy efficiency

« Last post by PCB.Wiz on Today at 01:32:25 am »

For battery capacity limited device, what is the 'sweet spot' duty cycle and frequency to drive LED at highest energy efficiency (high brightness using low energy) for human active observer for attention-seeking guide light. 

If you want attention seeking, you need to study human eye flicker sensitivity.
Peripheral vision is also more flicker sensitive, so you might end up with hundreds of ms of period and tens of ms of ON time for best perception.

Set something up that lets you adjust period and on time, in that ballpark and do some field tests.

5

Test Equipment / Re: Enabling options on Agilent ESA series E4402B E4404B E4405B E4407B

« Last post by BG8IP on Today at 01:28:52 am »

JUST LIKE THIS   

6

EEVblog Specific / Re: What's the keywords for finding a yellow spudger like Dave has?

« Last post by ballsystemlord on Today at 01:26:06 am »

@bdunham7 That is the physical form of the item. And certainly, the keyword "yellow" is in the description. But if you take the picture and put a yellow and an orange line next to them you can clearly see that these are not yellow.

That's CSS orange and yellow that I'm using. It has nothing to do with my palette or program that I'm using to "paint" with.

7

Other Equipment & Products / Re: PCBite is a brilliant oscilloscope probe holder

« Last post by shabaz on Today at 01:23:09 am »

They are also surprisingly low-cost, so it's almost as if the hands-free functionality of them is for free, if you need to buy a second set of probes for a 'scope anyway. The going rate here is £39 for the 100 MHz version, which is often more than sufficient for capturing various typical serial interfaces on boards as an example. The photo shows I2C being probed on a QFN chip.

The steel base can be DIY'd, to save purchasing that, if desired.

Since they look a bit delicate, storage needs a bit of thought (I didn't wish to disassemble the probes to put them back in the supplied flexible pouches), one possible solution to allow storing them fully assembled, is shown in the attached photo (the plastic case can be placed in any orientation and the tips do not touch anything).

8

General Technical Chat / Re: Powering an LED from international line voltage

« Last post by HackedFridgeMagnet on Today at 01:22:03 am »

Capacitive Dropper may suit.

9

Projects, Designs, and Technical Stuff / Re: MCU recommendations- looking for low pin count with more memory than ATtiny

« Last post by PCB.Wiz on Today at 01:14:43 am »

1. Calculate an audio range square wave's frequency from a rising edge interrupt
2. Update a SSD1306-driven OLED with that frequency info

What precision and accuracy do you need on that frequency reading ?
Low end MCUs have RC oscillators, of only moderate accuracy.
Better accuracy may need a crystal, or an oscillator.

Does it need to be 3.3 or 5V ?

If you want small, there are MSOP10 MCUs available,  Nuvoton ML51BB9AE is 16kF 1kR

SO-8 packages tend to be somewhat trailing edge.
If you are ok with SO16N, QFN20, or TSSOP20 there a (lot) more choices.


 

10

General Technical Chat / Powering an LED from international line voltage

« Last post by kenyonshutt on Today at 01:00:58 am »

Yo! I can’t believe I’m struggling with this, but I’m finding it really difficult to design a cheap circuit that can drive a 10-15mA LED, powered by a wide range of AC voltages (roughly 80-250VAC). It’s frustratingly challenging, given the fact that all kinds of products have “power present” indicators. That’s all I’m trying to do.

Some attempts:

• AC feeds LED directly thru a resistor (resistor needs to be super high wattage, LED brightness changes with voltage)
• Voltage divider with zener regulator (zener ends up conducting way too much current at high voltage
• wide voltage range LDO like onsemi NCP785AH50T1G (lots of components, this family is only rated to 10ma which isn’t quite bright enough

Sure I could add a friggin transformer or switching power supply but I literally just want the LED to turn on, at a predictable brightness, when the device is plugged into the wall.

Thoughts anyone? Thanks!!

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