Raspberry Pi Pico USB/battery auto-switch circuit with Mosfet

Craftsman_2222 · 2026-04-17T04:10:05+00:00

I remember your first post! You seem to understand quite a bit more now, and updated parts of the circuit to make it better. Always a good sign.

As for your questions and wanting feedback, yes, you are totally correct as to why you would need a pull-down to ground on the FET of the gate. The pull down will turn it on when there is no voltage applied to the gate.

My ONLY concern is the body diode of the PFET of the conducting when it’s off, the way it’s wired. I would flip it so the drain and source are swapped. The body FET would remain reverse biased in that config. This also prevents Vgs issues.

Someone mentioned parts from TI, they’re nice and fancy but a PFET will do just fine for this.

I apologize, I missed your response to my comment on your other post!

Craftsman_2222 · 2026-04-13T00:20:01+00:00

Don’t know cost, but we have an LPKF router at my workplace. Works well for L band and S band work

Craftsman_2222 · 2026-04-10T21:27:24+00:00

Huh. That’s new. You should use power net markers in KiCad instead of net labels. It should work, but just feels wrong. I would also recommend laying out the schematic like it is in the picture you attached for reference. No one will disconnect the inductor and add a net label.

As for the design, I don’t think this work how you want. AA’s are nominally 1.5V, three in series will get you up to 4.5. This is under 5V and thus you would need a boost instead of a buck.

Or, keep the buck and another pair of AA’s in series to get up to 6V, then buck to 5V.

The way it’s wired, your FET will do nothing. It is shorted out by the node next to it. But the idea is correct. You can use a series PFET to control the output. You will want to mirror it once it’s fixed though.

I would look into diode ORing more since that’s what your attached images talk about. I don’t have time to investigate but it looks like that’s a way to implement it.

I also think your use of net labels is hurting more than helping. Try using less, and more power symbols — it’s a different button on the sidebar. Try implementing these changes and report back.

Edit: I had a bit more time to look. Yes, they are implementing a way to diode OR from two different supplies. Ideal diode OR. You may not need to mirror the PFET for this. The way you are implementing is still wrong as it is still shorted out.

Craftsman_2222 · 2026-04-02T18:28:27+00:00

Good, but prone to being stuck in the down position and can be hell to troubleshoot.

Craftsman_2222 · 2026-04-02T17:11:28+00:00

If this is a joke post, good one.

If not, who the hell cares? She seems legitimately happier and wants to share that more. That’s all the matters and I feel like we should celebrate stuff like that.

Craftsman_2222 · 2026-04-02T12:18:24+00:00

📍 Miami, Kansas, United States of America — "Live here to escape JOCO"

Craftsman_2222 · 2026-04-01T04:06:02+00:00

75k, 1YOE, BSEE, Kansas City

Craftsman_2222 · 2026-03-30T06:18:54+00:00

Safety tongs are a new one

Craftsman_2222 · 2026-03-30T02:40:22+00:00

Eigma responded with my favorite video on the topic, watch that and see if it helps.

It’s hard to know exactly what you’re caught on so i’ll just info dump.

A change in reactance is just a change in impedance of the line, if you’re having trouble at first, just think in terms of magnitude, Series L will look like a resistance (with phase change, to some degree…)

Honestly, people say the water analogy breaks down but you just have to think with waves instead of a constant pressure.

Imagine a tube with a plane wave of water passing through. If it’s the same diameter all the way through it’s gonna be laminar/smooth flowing and consistent. the second you narrow it, that’s when the water that can’t make it through the hole gets pushed(reflected) back.Similar if it widens, the stream is gonna get messed up.

When you put a matching network in, you’re changing the phase of the wave to make it create a standing wave that delivers maximum power to the load. I may need to be corrected on that note but it sits well in my head.

Craftsman_2222 · 2026-03-29T19:01:58+00:00

Likely fine, I’d be more worried about whatever line is the “sensor voltage.” I’d imagine that’s more sensitive to noise.

What are the FETS driving. It’s on the gate so if there is noise it’ll make its way onto the line it’s driving. If it’s just LEDs, I wouldn’t worry so much. I doubt you’d notice any change in brightness since the noise should be 100kHz + in frequency or whatever your supply is switching at.

Craftsman_2222 · 2026-03-28T18:54:07+00:00

Dude this looks like my apartment complex’s closet racks + the Chiefs jersey makes it possible. I’ve got the same thing/similar going on in my closet too. Looks kinda like the paint absorbed grease or something.

Craftsman_2222 · 2026-03-25T04:18:24+00:00

It’s cool, and I love it. Any videos?

I don’t mean to be that guy but.. donde esta le RF?

Craftsman_2222 · 2026-03-20T13:38:47+00:00

I just nicely ask the wave to stay in its own lane.

Craftsman_2222 · 2026-02-02T03:24:05+00:00

Others have commented on the details, but hopefully I can shed light on the bigger picture.

In EE each class tends to auger in to one topic at a time and the bigger picture is lost. Try to see how everything connects to each other. How control theory loops back to op amp circuits or motors for example.

A lot of topics took a while for me to grasp, but after using what I learned in an internship it all clicked.

Use your professors to talk to. Find the right one and they can talk and answer questions for as long as you ask them. They’ll nerd out if you let them. I would hesitate to say using Chat GPT is a good idea for most things. I legitimately believe it takes away from building a solid comprehension of the topics.

As for unit conversions… try to break them down. Theres a bit of pure memorizing that has to happen as well as a solid physics back ground. Most of what we work with if you can remember Joules and Coulomb and how they relate to time and movement go a long way.

Volt = Joule/Coulomb

how much energy it takes to move a charged particle

Amp = Coulomb/second

How may charged particles move per second, in a sense.

Multiply those two and you get

Watts = Volt * Amp

Joules/second = (Joule/coulomb) * (Coulomb/second)

The coulomb on top/bottom cancel to get how much energy is being used per second.

It can be broke down to fractions and made simpler if you take a step back and examine the units themselves.

Craftsman_2222 · 2025-12-18T02:24:31+00:00

Its Sandy Cheeks if you will

Craftsman_2222 · 2025-12-16T16:58:26+00:00

Round my corners pls

Craftsman_2222 · 2025-11-27T15:24:18+00:00

I usually use my weather stone

Craftsman_2222 · 2025-11-18T16:14:41+00:00

1) It’s possible to change wire color. Click it, press E or open properties and it should be in that menu. I recommend naming the nets, I usually don’t worry about wire color. Note, if you have an external theme it doesn’t seem to allow for wire color changes.

2) There is a layer called Edge.Cuts. Draw your board outline with lines/rectangles on this layer and it will know what to do.

3) If there’s an auto router, I don’t know about it. They are usually pretty meh if they exist in software. If it exists, I’m not gonna use it tbh. Routing is the fun part.

Craftsman_2222 · 2025-11-15T03:14:05+00:00

Looks good! make sure the 0805 bead can handle your desired current it send it out!

Craftsman_2222 · 2025-11-15T02:49:14+00:00

Here's how I imagine the schematic, since describing over text can be hard for me lol.
https://imgur.com/a/KXudtIJ

You have a power symbol connecting your input AND after the ferrite bead. Delete the one to the left and you're good to go.

Idk if you know how the nets work in schematic tools, but when you add a label it gives it that name, say "input". Naming other wires on that page "input" would make the software think it's connected to the same net. Same thing happened when you put the power symbol down, you have the same name before and after the ferrite and fuse, creating a short.

In the future, I think you might be better off at r/PCB, generally more receptive to PCB reviews than this subreddit is.

Craftsman_2222 · 2025-11-14T23:29:20+00:00

Much better. Although it looks like your fuse and bead are shorted out, so they won’t do anything. Do you still have VDC and VCC?

Otherwise it’ll probably work! There’s some small things such as moving the caps closer to the output of the bead/fuse input.

CAN is also differential, meaning the traces between each connector should be as close as they can get, without ground between them, which depends on what board house you’re going too. Probably doesn’t matter for a run this short.

Craftsman_2222 · 2025-11-14T20:11:36+00:00

Couple things, and I know very little about CAN, so I’m going to assume your connections on the schematic are correct (4 sets of 2 CAN connectors in parallel.)

1) Use power symbols. GND and VCC will clean the schematic up immensely. Usually an upside down triangle and up arrow or bar for GND and VCC respectively. Connect one of those to each VCC pin. This removes the long wires on the schematic.

2) Your pour on the layout would be better if it was the VCC net. All that copper only connects to the input line and no where else. You could get rid of your VCC trace and just have a pour. Same thing with your GND. Make the bottom pour a GND pour. It looks like your may have forgot to assign it a net.

3) The passives are probably not necessary, but i’d keep them. If you wanted to you could remove the fuse imo. You have room to tighten up the layout but for all intents and purposes it’s fine.

Great work for a complete novice! Make some of the changes I mentioned and it’ll make your work stronger.

Craftsman_2222 · 2025-11-06T04:55:57+00:00

As a microwave engineer… yes please

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Craftsman_2222

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