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Forum section: electronics / general

author: dennis2oo4
author_rank: Newbie
timestamp: September 05, 2025, 01:57:21 am
content: delete (old post)

author: PGPG
author_rank: Frequent Contributor
timestamp: September 05, 2025, 09:35:21 am
content: In your description there is no word about RF antenna, but at schematic it is.At schematic antenna is connected to pin 1, but at 3D view I see antenna far away while pin 1 is near us.Your schematic is incomplete - there is no way to find Q1,Q2,Q3,Q4 integrated resistor values, what is the D2 type,Your schematic is sloppy - look near pins 53,54, I see R3 as 4k, need magnifying glass to see that C6 is C6, some connection dots looks 'shifted' (see R9, C19, GND wire near USB1) - these generally says that someone scatterbrained did it,Mimicking at schematic physical element construction (Y1, USB1, U3, U4, Q7) is not the best idea - try to understand what Q7 is doing (if its transistors were drawn separately and in normal positions it would be easier).D2 has a standard diode symbol (not Schottky) so you loose at it more than 0.7V. It is important - you loose here at your own request about 20% efficiency. Your DCDC 5V->12V converter practically get 4V at input. Do this diode was used to protect against someone insert USB-C inverted ?

author: EDADOC
author_rank: Newbie
timestamp: September 07, 2025, 05:28:32 am
content: :)This really doesn't seem to be a good design, especially trying to keep the antenna part as straight lines or curves.

author: Nominal Animal
author_rank: Super Contributor
timestamp: September 07, 2025, 08:38:27 am
content: Quote from: PGPG on September 05, 2025, 09:35:21 amThis is obviously donein EasyEDA, and in the 3D view the chip is rotated 90°. In top silkscreen you see pin 1 marked. In the 3D image, pin 1 is far away from us, in the back right corner, with the component right to it being L2. The three vias nearby are unrelated, not connected to the antenna circuit.

author: PGPG
author_rank: Frequent Contributor
timestamp: September 07, 2025, 11:13:10 pm
content: Quote from: Nominal Animal on September 07, 2025, 08:38:27 amWhen you designing (anything) you should be careful and thorough. I have noticed that it is rotated, but just wanted to show that overlooking such easily noticeable details reflects poorly on the designer.

author: PGPG
author_rank: Frequent Contributor
timestamp: September 08, 2025, 10:08:35 am
content: Quote from: dennis2oo4 on September 08, 2025, 12:21:32 amYou didn't got answer (till now) because may be no one here knows answer to this question.I suppose there are two kind of forum users:1. Wanting to learn electronic - they try to solve their problems themselves (with forum help) - so don't even consider external design review service.2. Wanting to help other people to learn electronic - they don't need others to revise their designs - so also never considered such service.I suppose my way in electronic was typical. Being 10 I build my first (detector) radio receiver. Being 12 I finished copying others schematics and stared to design my own. Year after year more and more complicated. So from my point of view typical is to design devices that are on border of your understanding.You are trying something (in my opinion) not typical - to design device that seems to be far away of your understanding.I think you should learn to know what you are doing.1. If load is relatively high (12V/400mA) than converting 5V->12V is clearly easier than 4V->12V. It is why I was looking what is voltage drop from 5V USB supply to your +5V net (it should rather be named +4V) and it was why I wanted to know if D2 is standard or Schottky diode. But there are no type written. So the only what we can find is its symbol being standard diode symbol.2. Second question is - what for is this diode used at all. I have no big experience with USB. Do someone have rationale to assume that some USB supply can give you reversed voltage?3. Q1..Q4 are expected to switch 100mA load. It depends on the integrated resistors if they will be able to do it. So I wanted to check them - but like with D2 - secret information. We don't know what is the rationale for using 'digital transistors' here. May be someone have thousands of them and just uses everywhere to not have to buy other elements. NMOS seems being much better here.

author: Nominal Animal
author_rank: Super Contributor
timestamp: September 08, 2025, 11:25:31 am
content: I, too, suspect the OP is not interested in learning electronics, and just wants this gadget made. This is not the right place for that. OP could post about this in theJobsboard here, explaining the needs and wants, and optionally linking back to this thread for details why the existing design isn't a good one.Quote from: PGPG on September 08, 2025, 10:08:35 amIt can only happen with a bad USB cable that breaks devices.Sometimes a P-channel MOSFET is used for polarity protection, for example in microcontroller developer boards. Then, drain is connected to USB VBUS, source to +5V used in the circuit, and gate to USB GND.Diodes Inc. DMP2035Uis a commonly used one for this in SOT23-3 package (3mm × 2.5mm). During normal use, because gate-source is -4.5V (or more negative), the drain-source resistance is typically just 23mΩ, maximum 35mΩ, so the voltage drop at 2A is maximum 0.07V, and 0.14W is turned to waste heat. It'll get a bit warm at 2A, heating by about 22°C (40°F) above ambient, so I'm not sure it's the best option here.When the device is connected to other externally powered devices, or is externally powered itself, then it is important to not back-feed power to the USB host. I like using TI LM66200 for this, as it acts like a pair of ideal diodes, with very little voltage drop or waste heat generated. It can only handle up to 5.5V, however.Quote from: PGPG on September 08, 2025, 10:08:35 amExactly, say aToshiba SSM3K2615Rin SOT23-3F (3mm × 2.5mm). When driven from 3.3V logic, the drain-source resistance Rds(on) is typically just 0.38Ω, maximum 0.58Ω. At 100mA drain-source current, it will drop less than 0.06V, and generate less than 0.006W = 6mW of heat. It can handle the 12V between drain, gate, and source, and is pretty cheap too.I'd also use a 100Ω to 10kΩ resistor, for example 220Ω, between the gate and the microcontroller output pin, to ensure that when the MOSFET switches, the peak current draw is at most 3.3V/R amperes. MOSFET gates behave like capacitors, and only draw current when switching state; the resistor will slow that switching a bit but also ensures that the microcontroller output pin is not stressed too much. A resistor of 220Ω with 3.3V logic limits the current draw spike to less than 3.3V/220Ω = 0.015A = 15mA.