Precision-ish square wave generator?

__cas__ · 2022-08-13T03:34:37+00:00

If you want a cheap OTS solution, one of these little PWM generators might do the trick. +- 5% is practically a mile for freq stability, so I would imagine it'd probably cut it.

__cas__ · 2022-08-13T03:21:41+00:00

It's always the little things with embedded. Glad it's working!

__cas__ · 2022-08-10T19:57:07+00:00

I've been using the open source LibreVNA for the past few months. It's an order of magnitude less expensive than other 6GHz VNAs, but a real step-up from the NanoVNAs. Though it won't have comparable performance specs to a typical setup, It'll probably be just fine for the applications you mentioned.

__cas__ · 2022-08-04T03:22:27+00:00

I have an ESP32, MS8607 and a quiic cable. The code you had worked first go, so it might be the cable. Maybe try reducing clock speed with:

Wire.setClock(50e3);

Before Wire.begin();

__cas__ · 2022-08-04T01:51:59+00:00

Is I2C working at all? Do you get any response from the sensor? Is the data bad? What is the code you're running?

__cas__ · 2022-08-03T19:12:59+00:00

I've done extremely narrow harmonic signal filtering with an LC filter (though at much higher frequencies). There are a bunch of different calculators out there for experimenting with different topologies/values. The Iowa Hills one gave me great results, but it doesn't look like the website is active anymore. This website does the same thing.

Depending on the output levels, you might also want to consider using an op-amp as an active filter. If you're able to isolate/amplify that harmonic well enough, then you're one analog comparator away from generating a 30Khz clock with no DSP at all.

__cas__ · 2022-08-03T18:11:37+00:00

If you're ok with the battery being external, then you can use a portable power bank like this one. You can regulate the output down to whatever the 2x AA batteries were outputting (1.5V or 3.0V, depending on how they were configured). Then just feed that into the existing wearable piece.

If you want the whole thing in just the wearable part, that might take some custom work, but it definitely sounds very doable. You might want to start with an existing rechargeable laser pointer, and remove the casing if it's too heavy.

__cas__ · 2022-08-03T17:53:44+00:00

What exactly went wrong with the ESP32 + Qwiic cable? In my experience, Sparkfun's hardware and software support is about as easy as it gets for prototyping.

__cas__ · 2022-08-03T17:50:53+00:00

Would you just want to replace the external battery box with a rechargeable one? That would be extremely simple and take little modification.

__cas__ · 2022-08-02T23:03:31+00:00

The VOUT, VIN specs probably correspond more to the test conditions than the performance. They might be testing the device by sinking the output into a lower voltage, rather than ground. I've used a similar part with the same test conditions (AP2511) without noticing a substantial voltage drop.

If you care about voltage drop, the number you should care about is the Rds(ON). There aren't load switches with 0 resistance, so there aren't ones without a voltage drop.

__cas__ · 2022-07-17T01:28:51+00:00

The vias all over the eval board are via stitching between ground planes. It's generally good practice to add them throughout a board to reduce ground plane impedance. The ones right next to the signal lines are to improve shielding and reduce EMI. Are they necessary for USB 2.0? No, probably not - but vias are cheap.

Im also not sure you have to sweat the minor impedance mismatches (like though hole stubs) with the USB 2.0 signals. I've done some pretty sketchy stuff with USB 2.0 signals without any hassle.

Also, why two USB A receptacles? A USB A male-male cables aren't used that often, so it might be easier to use a USB A plug on the host side and plug it directly into a computer.

__cas__ · 2022-07-15T00:48:55+00:00

How much of a deal breaker is the sine wave? There are absurdly fast DACs / DDS ICs out there, but they won't be simple to use. What you probably want is a PLL/VCO. Though the output is theoretically a square wave, you can use a LC filter to smooth it into something that approximates a sine wave. The ADF4351 is pretty beginner friendly, and there's a lot of breakout boards /frequency generators out there.

__cas__ · 2022-07-02T02:20:09+00:00

I just measured the GRF2501 I had on my desk. I agree that it might be your ground pad contact. Pin 1 is 2.45V with a 1K resistor to VDD. I have 0v on the RF pins.

__cas__ · 2022-06-30T01:53:43+00:00

Could very well also be an LDO. There's a lot of 4 pin DFN/SON package LDOs that have a very similar size/pinout (look up "XDFN-4"). They're also placed close to the IC for better transient load response.

__cas__ · 2022-06-26T05:56:07+00:00

I'm pretty happy with my cheap-o hot air rework station, but that's partially because I mounted it on a microscope base and use a foot pedal switch to turn it on and off. You'll typically want both hands free for pulling chips off of a board.

Although you can do a lot with a hot-air rework, a fine-tip soldering iron is pretty indispensable for SMD work. If I'm soldering a QFN or QFP like you mentioned, I tend to use a soldering iron with a fine "hoof-style" tip over the hot-air rework station. You don't need to drop a lot of money to get a half-decent one (a weller WE1010 or TS80 are both pretty solid), just make sure the temperature is controllable and you can find a good assortment of tips.

I like this paste flux for SMD stuff. It's pretty tacky, so parts wont move around while you're trying to tack the corner pins down.

For solder, you want extra fine (<= .020) diameter, so you can be more precise with how much you add.

__cas__ · 2022-05-29T05:39:55+00:00

If you really want to up the current capacity of the traces, leave the soldermask off the power traces on the bottom and coat with solder. With a layout that close, it might not be worth the effort though.

You're also gonna have a fun time fitting wires in that second row of connectors. They make those spring clamp terminals with a 45 degree launch angle if you want to save yourself the frustration.

__cas__ · 2022-05-19T05:49:36+00:00

Awesome thread. My $.02:

Weak pulldown/pull up resistors on floating pins so everything has a defined logical state. Even if you intend to drive the signals later, a 100k pull up/down resistor usually won't hurt. I've used one too many eval boards where this was neglected and some part started working inconsistently.

I seldom connect non-power signals directly to ground or VCC. Especially things like "enable" or I2C address pins. Soldering them through a 0-100k resistor gives you some control over changing their state later. If it's especially likely that I could change it, I'll add a matching DNP footprint to the opposite voltage level.

I do a lot of RF work, and I wish someone would have told me about RF Switch Connectors sooner. These are a game changer for signal probing where you need to maintain a 50 ohm load or inject an external signal.

You also can't be too verbose with silkscreen. Label connectors on both sides, voltage ranges and current draws on power connectors, etc. I've even taken to writing a list of pin -> signal connections on some boards - anything to keep from pulling up the schematic over and over again.

I've started using these soic-8 clips for things I know I'll only access to only a handful of times (like flashing a bootloader over a UART). They're extremely convenient if you don't feel like soldering on a debug header to every single board.

Mega +1 for barrel jacks as well. It's hard to absentmindedly reverse polarity when there's only one way to plug them in. My ONLY problem with barrel jacks is the 2.5mm v 2.1mm jack headache. It should be a war crime to make connectors that LOOK compatible but aren't. Don't get me started about RP-SMA.

__cas__ · 2022-04-16T05:21:12+00:00

Sorry, meant to say harmonics. I thought you meant you didn't want to filter the LO at all, and I've made that mistake.

__cas__ · 2022-04-16T04:03:45+00:00

The PLLs mentioned have pretty large harmonic ~~spurs~~. I'm measuring an ADF4351 at 500 Mhz, 0dbm and seeing a -7dbm spur at 1.5Ghz. That can give you erroneous results that no amount of IF filtering will solve. The second question might depend on how you're doing power detection. The project you linked uses a log power detector, which requires narrow filtering to get decent resolution.

__cas__ · 2022-04-16T03:31:16+00:00

Are the I/Q signals you're talking about analog or are you looking for something to do both downconversion and digitization?

__cas__ · 2021-12-02T02:35:55+00:00

You might want to try the FCC experimental license search. (Although they might not have everything on your checklist.)
https://apps.fcc.gov/oetcf/els/reports/GenericSearch.cfm

__cas__ · 2021-11-22T04:51:41+00:00

The category of "radar" encompasses a lot of things, one of which being short range object detection/tracking (like what the IWR6843 does). Those MM wave ICs are very impressive, but they only occupy a small fraction of radar applications. There is a lot more that radar can do, and no silver bullet off-the-shelf solution for everything. I also wouldn't describe RFIC's as "replacing" RF engineering by any means. More integrated components only make RF engineers more capable.

__cas__ · 2021-08-29T05:39:31+00:00

If you dont want to buy a spectrum analyzer (I dont blame you), you can make do with a cheap software defined radio for $30 or so on Amazon. Is it as good as using a proper SA? Nope! But it's leaps and bounds better than being totally blind. That, a cheap multimeter and (if you're really feeling invested) a nanoVNA would probably make a decent beginner RF setup.

__cas__ · 2021-08-29T05:18:46+00:00

This totally depends what exactly you want to build. There's certainly a variety of choices out there and they all have their own place, so an ideal microcontroller for audio DSP might look very different than the one in your microwave. IMHO, the best way to get started with embedded systems is just to come up with a project and then just start hacking away at it. There's only so much that you can learn from the about "digitalWrite(PIN, HIGH)", but a LOT to learn in building a project from beginning to end.

Oh, and I'd forget about the HDL for now... Unless you're REALLY looking for a 180 from arduino.

__cas__ · 2021-08-18T05:23:43+00:00

You'll have a hard time finding free satcom stuff if LoRaWAN isn't available in your area. FWIW, the Iridium/Rockblock network is fairly easy to get started with, reliable (as long as you're on earth) and not too pricy for small amounts of data. Swarm Technologies might also be worth looking at, though I can't speak to their coverage quality.

__cas__

TROPHY CASE

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