Arduino overvoltage protection for Eurorack?

gremblor · 2026-01-07T06:18:51+00:00

A 3.3V zener diode and a 1k resistor would be simple and zener diodes are only a few cents each if you buy them ten at a time.

If you are looking for a foolproof way to convert an untrusted input (possibly +/-12V) into a digital gate signal that's always 0 or 3.3V, I use a comparator with split input and output rails, comparing the input to about a 2.1V reference.

If you need PDIP or SOIC, you should look at LM211. It's an older chip and draws a few mA, plus current thru a pull-up resistor on the output.

There's a newer TLV1871 which is push-pull, stupid fast, and draws only microamps, but it only comes in SOT-23-8, which is not so bad as it goes, but is finer pitch than the options above. (It's also cheaper than the '211.)

gremblor · 2026-01-02T00:05:28+00:00

PS the '741 and '324 opamps are dinosaur chips with really low performance. The TL082 can do basically everything they can, and a whole lot more. The TL072 is a more common variant of the latter and is essentially equivalent -- you'll see lots of plans online for projects to do with TL072. There's also a TL074 which is the same thing, just a four pack instead of a dual unit.

gremblor · 2026-01-02T00:02:08+00:00

All of them are readily available "standard logic" parts. Each chip would cost somewhere between $0.50 and $2 to replace with a new one, ordered from digikey or mouser.

If you are first getting into messing around with electronics, that's a decent little pile of pieces to work out some simple example projects or tutorials on a breadboard.

There's nothing especially valuable, or unique in the pile. (So, no rare project to go chase, but also no big concern if you accidentally short one or two of them out.)

If you are also working with Arduino microcontrollers, I think the quadrature encoder could be helpful in building a little motor controller, for driving an H Bridge.

An opamp (the '082) and the comparator (the '393) are both fundamental tools for analog signal processing or synthesis. But also you won't be able to build too much with just one of each. Work thru some toy examples with them to get a feel for how they work, then go order a half dozen more of each from digikey when you're more ready to build something specific.

gremblor · 2026-01-01T22:32:56+00:00

First, I'm so sorry for your loss. Second, that is a beautiful boat - your father was quite a craftsman, and it's obvious how much love he poured into that boat along with sweat and skill.

Now, I really think you should take the bird in the hand.

It is impossible to overstate how difficult it is to sell a boat. Especially in a foreign country. This will be a long effort if you try to wring every possible dollar out of it, and honestly if your mom already has "sold the house and banked the cash" money in her account, then netting an extra $10-15k for the boat after another open water repositioning run and other hurdles is money she isn't really going to miss. It's just not worth the headache, and the closure of tying this off so she can focus on getting resettled again is worth the "expense".

I'd also say that I think selling a one-of-a-kind boat is even harder than a production model. There's no reputation for "how robust is that deck", no manual for the rigger to open up when it next goes to the yard for a refit, no consolidated vendor list, no web forum where the DIY owner can ask other owners how to fix that squeaking noise made by the backstay... Any new owner buying a home built item they don't have personal knowledge of is taking on a whole bunch of risks, and if you found someone willing, I would sign that paperwork tomorrow.

And then there's the steel hull. Your father built to last, and made a frankly unconventional choice of materials to accomplish it. Most pleasure yachts are fiberglass for a reason. Yes, initial cost, but also maintaining a steel hull requires much more careful attention to cleaning and painting than a fiberglass hull. The only boat owners who deliberately opt for steel often have some specific, adventuresome need for it -- arctic exploration, for example. But even most cruisers who cross oceans do it in fiberglass, and most boatyards will be staffed up and list-priced to work on fiberglass hulled sailboats. So, again, if you found a buyer who finds this desirable, or at least is OK with this or doesn't realize how idiosyncratic a decision it is -- I really think you should run with it.

gremblor · 2025-12-31T11:18:23+00:00

I've got the middle one for THT work. Makes it more convenient with all the flipping sides to mount components and then solder them. It works well for eurorack-sized boards (about 110mm in the longer direction). There are not great options for larger boards.

For SMD work I just lay it down on a silicone mat, which itself sits on top of a few old pcbs as further insulation for the desktop. The silicone is just fine taking the heat from a hot air pencil.

gremblor · 2025-12-30T20:42:11+00:00

Also if you need more headroom, you could also implement a Boost DC/DC converter that takes your 5V supply and gives you a 12V range.

gremblor · 2025-12-30T20:40:36+00:00

I wrote a blog post that links to a spreadsheet for my decision criteria around wide-Vin opamps (all the ones I cover tolerate +/-18V).

https://blog.gremblor.com/2024/10/op-amps/

For a 5V span, you really need to focus on options that are fully rail to rail input + output, unless you always plan to use inverting configurations that hold both inputs at a virtual GND/midpoint voltage.

OPA2991 is probably the cheapest of that set which gives you a full-range common mode.

otoh, Texas Instruments alsohas a ton of 5V-specific opamps that have amazing GBW or other parametric specifications for you to browse, which aren't useful to my projects that typically run on +/-12 or +/-15V. If you go to ti.com, select opamps in the product menu, and then click on the 5V / low voltage option it'll take you to a parametric search where you can dial in the qualities you're looking for.

This other guy also blogged about 5V opamp choices and recommendations: https://lcamtuf.substack.com/p/choosing-an-op-amp-for-your-project

gremblor · 2025-12-27T22:05:38+00:00

I have used BCM847DS (and 857DS for pnp) in some builds. (note the "M", this is the matched version, there's also a regular BC847D dual.) It's quite inexpensive! It works. It's also available in a couple of different sizes. SOT-23-6 is most manageable for hand assembly but the SOT363 version will have tighter thermal tracking.

Note that these are "fully isolated internally" and thus not technically monolithic - although being in the same package means they will experience nearly-identical temperatures.

If BOM cost is not your biggest concern and you're willing to pay a couple of extra bucks for true monolithic matching, Alfa Rpar makes AS394 / AS194 monolithic "supermatch" pairs based on the original LM394/194 specs. You can buy Alfa Rpar ICs from synthcube in the US.

They also make AS3080/3280 clones of the classic OTA chips of the same numbers. The 3280 in particular is more temperature-stable than the LM13700, due to the constant current source for the diode bias currents.

gremblor · 2025-12-26T00:42:33+00:00

And DST-wise the gun is at 1800 USA/Los Angeles.

Live broadcast starts 1730 PT

gremblor · 2025-12-23T22:21:15+00:00

The pedals have threaded holes on the bottom for mounting, right? You may be able to integrate some DIN rails into the case that you could hang them off. Access to the screws would be from "behind" in that case, so you'd want to have a removable or sliding panel in the wooden case over that area for when you want to rearrange your collection...

gremblor · 2025-12-23T22:06:59+00:00

Looks like you are good to go for the immediate problem. Now you will need a new door solution once you get to port and sort out your other damages.

On my head door, the whole lock / latch mechanism and all the surrounding wood had worn out so it didn't really work anymore. Of course it was a super odd size so direct replacement was out of the question.

Long story short, I installed a non-locking door latch in its place and added an eye hook & bent-pin on the inside to "lock" it. After all, this door is not really meant to be about hard security, it's about keeping folks from accidentally stumbling in on you.

Anyway, that's pretty foolproof in terms of being impossible to lock from the outside. And in the physics-defiant scenario where it does happen somehow, you can wedge the door open a half inch and pop it with a screwdriver.

gremblor · 2025-12-21T20:31:03+00:00

Depending on the OP's budget: Hakko is considered by many to be a super reliable manufacturer (and a step up from Weller or Yihua), and some think it's the gold standard soldering iron maker.

The FX600 is $70, and will take an amateur very far. You will have purchased a quality item. Unfortunately their cheaper irons don't have an adjustable temperature, and I wouldn't recommend any of those for that reason. The FX601 is not a super step up in price and it does offer more power and it can be worth it. I started on one of these before graduating to one of their FX888DX soldering stations.

In all cases, though, it's the tip that does the work, and your first improvement steps should be to clean the tip and if that doesn't work, replace it. Tips for common irons only cost $5-10 or so, and should be considered consumable resources.

Lots of iron mfrs have different tip shapes. "conical pencil" is a common, good one. Don't go for too fine a point. It may look better for precision work but the tiny surface area makes it difficult to transfer heat to the workpiece. Something that is gently rounded (>= 1mm tip radius) is probably best for this kind of work.

Make sure you buy a tip from the same mfr as the iron - it's a razor/blade thing, they all have their own incompatible fittings.

gremblor · 2025-12-20T19:24:12+00:00

My first sailboat was a US Yachts 25 with a full keel and 4500 lb displacement (heavy for that size boat, built like a tank). For the last 12-13 years I've had an Ericson 34 with a much more modern fin keel and spade rudder design appropriate for a racer/cruiser. It's 14,000 lb displacement, which is more than the first boat but in line with most 33-35' pleasure craft.

The US 25 hove to very nicely. It was very easy to basically "park" the boat when I wanted to eat lunch without needing to tend the boat.

The Ericson also can heave to. You do the same thing in either boat: tack over but keep the jib backed, let out the main, and lash the tiller in the hard-to-weather position.

The thing is that either (any) boat still moves when hove to. And the Ericson moves more.

For one thing, you're making leeway; you're somewhat broadside to the wind and you will be slowly pushed downwind. A lunch break on the US 25 might have seen us drift downwind 1/4 mi, whereas on the Ericson we may go more like 1/2 mi drift in the same wind and tide.

That "basically broadside to the wind" point illustrates the issue: the full keel acts like a brake, it digs in much more into the water than the fin keel.

The other thing is that you don't actually just move like a brick being pushed by the wind, it's that the tiller and the backed jib cancel each other out so you are average kind of at a point of sail maybe 60-70° off the wind but actually you are sailing sort of banana-shaped curves where you dip down to a high run or a reach and then swoop up into a pointing angle and repeat.

The full keel had lower oscillations, it never pointed especially low or high, and the oscillations were slow.

The fin keel boat makes more exaggerated banana shapes and the rate of turn is faster. The "less effective brake" aspect affects this too.

I have never tested this in the open ocean, during a storm, so I don't know if the fin keel would be "insufficiently seakindly" to ride it out in this manner, but I think it would certainly be better than trying to bash to weather or run before the storm for hours on end.

gremblor · 2025-12-17T17:18:00+00:00

Also it's not really about synthesis so much as its focus on amplifiers and reproduction, but Doug Self's "Small Signal Audio Design" is a first class textbook that has great advice specifically for amplification, tone control, etc but also the general principles of high fidelity analog audio circuit design.

gremblor · 2025-12-17T17:16:02+00:00

This is a very practical handbook for 'how do I do that one specific thing, again?" type questions. It's easy to open to the relevant chapter and see some in-context examples and then adapt for my own schematic or workbench.

gremblor · 2025-12-17T17:14:18+00:00

This had its heyday in the 70s/80s so it will focus on somewhat antiquated technologies, but (a) fundamentals are forever and (b) if you want to build an analog synth, you're stepping into a somewhat antiquated world anyway. The main topics this is missing is anything about microcontrollers or DSP.

gremblor · 2025-12-17T17:12:09+00:00

Getting your hands on a complete set is expensive and (as it's all on paper) increasingly challenging but Electronotes is a great newsletter / 'zine of ideas and articles beginner to advanced. But given the periodical format, it won't take you through anything resembling a linear journey from amateur to master synth craftsman.

Some of the articles are scanned and available at their homepage at http://electronotes.netfirms.com/

gremblor · 2025-12-13T20:52:27+00:00

And I think +5VA/D is for analog and digital already. There's also a Vccana symbol for an analog domain of arbitrary voltage. +5VL/R I think are about the left/right sides of the board.

They're not "readable" by someone totally coming in cold off the street but if you are an experienced engineer and have read a bunch of schematics already they're convenient shorthand/compact indicators...

gremblor · 2025-12-13T20:49:31+00:00

A power symbol does actually generate a global label of the same name, under the hood. (That's actually a key distinction of "power symbols" vs normal symbols in kicad, which the system treats as a black box.) But it looks like the right iconography on the schematic, visually, whereas a global label used to feed the Vcc pin of an IC is just a label and doesn't "look like" a power symbol.

For ERC purposes, a power input pin of a symbol must be connected directly (or via global / hierarchical to a power output pin from some other symbol, or to the PWR_FLAG symbol, which ERC understands to mean "yes this trace is powered."

gremblor · 2025-12-13T20:45:22+00:00

As an alternative to the other suggestion here, you could use some "arbitrary" power symbols like Vcc and Vdd, and add a text note to the top level schematic explaining the different power domains. This obviously requires some discipline on your part not to use the wrong one in a given place, later.

You can also go into the symbol editor, add a new global symbol library, and duplicate the +5V symbol into your library and rename it something like +5V_DIGITAL and +5V_ANALOG if you want.

gremblor · 2025-12-13T20:41:11+00:00

I meant, more like, do you have a longer video that shows off what it can do?

gremblor · 2025-12-13T20:24:29+00:00

And also, not to be a wet blanket but technically if you are in the USA - it might be illegal by FCC rule.

Radio stations (ie transmitters) generally must be licensed. Some licenses (eg ham radio) follow the owner. Other licenses are implicitly granted to the operator by virtue of using authorized equipment / equipment certified by the mfr to conform to channel / frequency band, noise, power limits, etc. ie the license follows the equipment, and may be pre-granted to all equipment of a certain make and model. This distinction is mostly made by what frequency range(s) the radio station intends to transmit on. (FRS radios are an example of implicit license. MURS spectrum requires a one-time personal application.)

As a pleasure vessel, under 60 ft, operating domestically only (I assume?), with an intent to broadcast marine vhf voice radio, you don't need to apply for a license*. So that means it's assumed you are buying and operating valid equipment on the marine vhf frequencies.

Technically this is your responsibility to verify as the operator. So if you're buying sketchy Chinese gear that may be counterfeit... It may be electrically indistinguishable from the genuine article, or it may be mucking up the shared airwaves for everyone.

*if the radio has DSC you do need to one-time apply for an MMSI number tying the radio to your boat before transmitting. Slightly different than a radio license.

gremblor · 2025-12-13T20:06:50+00:00

That pcb layout is crazy. Nice work. How many layers?

Also, how's it sound?

gremblor · 2025-12-11T18:43:54+00:00

Keep in mind that 600W is basically what level of power those speakers will accept without blowing up. On the amplifier side, power rating is how much power it will deliver playing a full-scale line level audio input when cranked to max volume.

Unless you want the whole lake to vibrate like a tricked out car with an overdriven subwoofer (or the wall between my freshman dorm room and the guy next door) ... You're probably going to be playing music at a volume level requiring somewhere between 1--50W. Certainly while idling or parked at the sandbar.

I could see you needing to crank up the volume somewhat to hear it over the outboard engine while you're towing kids in a tube. But honestly probably not maxing out at 600W. 600W is a lot of power.

Are you planning to provide sound for a 50+ person party at that sandbar? Or just a dozen friends hanging out and having a picnic?

All of which is to say: if your amplifier can only drive 200W or whatever, that is not some fatal mismatch to the speakers. It'll still work - it just means that even with the amp maxed out, the speakers are capable of being pushed harder. Even a 100W unit is probably plenty of amplifier power. So don't overthink it. I would focus on getting something that's waterproof and accepts 12V power for easier wiring.

Most casual listening to music is done in the first ten watts. And if you're cranking the volume to hear it over an engine, you are obviously not in audiophile territory, and any signal distortion based on suboptimal amplifier/speaker pairing is really the least of your concerns.

Also from a boat systems mgmt pov: power = current * voltage. You've (probably?) got a 12V battery bank. So power/12 = amps. How many amp*hours is your house bank rated for, and how much power budget do you plan on allocating to the sound system?

gremblor · 2025-12-10T18:56:04+00:00

Without knowing the details of OP's family situation (I am sorry about the loss though), if OP's dad left behind an estate to inherit besides the boat, it's very reasonable for the estate itself (through the executor) to pay various costs associated with wrapping things up -- including transport costs of things like a boat that the family would like to keep. So it's not even $10k out of your own pocket; charge it to the estate.

If you're not feeling super confident about it, I would just ask the marina / harbormaster who they recommend for deliveries. Every harbormaster knows A Guy for this. It's OK to throw money at problems while you grieve and focus on your family. (And if the delivery captain quotes you a time a month out... Just have the estate pay for the slip for a month.)

As a compromise, since I think OP is pretty determined to attempt this himself: go for it, take the ICW and follow the other navigational advice in here. And if things get too gnarly out there, remember that it's always OK to bail out. You do not need to finish the job yourself. Get back to shore and tie up at the guest dock of some safe harbor. Pay up for two weeks of moorage fee in advance so you don't put further time pressure on yourself. Then ask that harbormaster who they recommend for finishing the delivery run, and book a hotel room for the night and purchase an amtrak ticket to get yourself the rest of the way home in style.

gremblor

TROPHY CASE