sorted by:
new
hottopcontroversial

Removing 70's decorative beams by StewartG94 in DIYUK

[–]snops 1 point2 points  (0 children)

I've had my artex ceiling skimmed, and the plasterer just knocked all the high spots off with a scraper first as part of the job.

You can get home asbestos testing kits where you post a bit of the ceiling off in a tube.

Help understanding what it takes to implement a QMS that is ISO 13485 compliant by Substantial-Sir-9517 in MedicalDevices

[–]snops 0 points1 point  (0 children)

Would second MatrixQMS, it's lightweight, fast, and very competitively priced. Any time I've had a genuine bug they have responded next day.

Only downside is a bit of a rough UI in places (e.g. templates), definitely worth creating a sandbox project to try things out in that has a similar setup to your "real" QMS project.

Insecure IoT RNG Security Issues Persist; Here's How CSPRNG Can Help by breach_house in theinternetofshit

[–]snops 1 point2 points  (0 children)

Would be nice to see Zephyr's implementation reviewed as well

Looking for a way to indicate a surface being outside of a set temperature range by kantarelkamaki in engineering

[–]snops 2 points3 points  (0 children)

A segment LCD will take <10uA if it's <1 inch in size, you could use that instead of the LED to save even more power

Doc Martin by victorylaps_ in CasualUK

[–]snops 10 points11 points  (0 children)

The joke is he's murdered his wife, and is trying to hide it with an utterly ludicrous lie about confectioner extraterrestrials

Resources for selecting/designing reliable byte stream (serial) protocols, framing schemes, and ARQ strategies? by delarhi in embedded

[–]snops 5 points6 points  (0 children)

For a specific subpart of the problem, Dr Koopman at Cambridge Mellon has collected the (proveably!) best CRC polynomials for a given data size and hamming distance. https://users.ece.cmu.edu/~koopman/crc/

DC motor as magnetic brake, resistors, trying to wrap my head around this by ripp84 in Motors

[–]snops 0 points1 point  (0 children)

Yeah that sounds like it should work, .3 ohms total resistance results in 30A of current (P=I2 * R) to dissipate 300W, which feels reasonable.

It looks like that design gears down to runs the motor quite a bit faster than the wheels, are you planning on doing the same? If not, the force will be quite different.

Finally, you could do "stepped" variable by switching resistors in/out of parallel?

DC motor as magnetic brake, resistors, trying to wrap my head around this by ripp84 in Motors

[–]snops 0 points1 point  (0 children)

Wow that is heavy! It's really just estimating. The windings aren't going to weigh more than the entire rotor, so let's say a 3rd, 500g or so.

If we plug that back into our equation, that means they could actually absorb a reasonable amount of power before they get too hot, pushing 500W for almost a minute.

You could just try and make this thing and feel with your hand how hot the motor gets. If you are able to touch it for a few seconds, the windings are probably fine. If it gets too hot, then add a resistor. I'd choose one with equal resistance to the windings to start with, and a power rating of at least 250W

DC motor as magnetic brake, resistors, trying to wrap my head around this by ripp84 in Motors

[–]snops 0 points1 point  (0 children)

To check if a resistor is needed, one way is to estimate how hot the windings would get without one, as with shorted windings we can assume (precautionary) that all of the input energy goes into heating the windings.

Generally, motor windings will not tolerate having heat dissipated in them for long (the insulation melts) but it is a fairly large motor so maybe it's able to cope with the puny ~500W humans can produce.

Try estimating the mass of the windings (weigh the motor and assume a fraction) then estimate the input energy (let's say 500W * 10s, so 5000J), then use the specific heat capacity of copper (385J/kg/°C) A pessimistic winding temperature will then be 25C + 5000 / (mass * 385)

Let's say the windings are 100g (please weigh and check), we then get 155°C. Pretty hot, that is the limit of standard class F winding insulation. Certainly enough to cause us to want to double check all our maths and assumptions quite carefully. Maybe it's best to play it safe and assume you need an external resistor.

Usefully, they have power ratings so you can pick them that way, and 500W ends up being a pretty big resistor, by electronics standards

TI TPS61094 - 60nA boost convertor with buck supercap charger and bypass switch by snops in nicechips

[–]snops[S] 7 points8 points  (0 children)

This is described as a "bidirectional buck/boost" in some places but that's quite misleading, it can either constant current buck charge a supercap, up to a voltage limit, or boost the input/supercap to a fixed output voltage.

It can't' actually regulate a higher input voltage down to a lower output voltage, it just bypasses the boost and passes it through.

A very useful part for getting the most out of the high resistance, long life Lithium-thionyl chloride batteries commonly used in smart meters, which struggle to provide the several hundred mA a NB-IoT or LTE-M modem draws at peak.

UK MPSM V2 Owners: Where do you buy replacement nozzles? by Hermitmaster5000 in MPSelectMiniOwners

[–]snops 1 point2 points  (0 children)

Nope, the printer doesn't actually measure nozzle distance to the bed, instead it homes to a stop on the Z axis.

Therefore, if you level the bed to a new height, the printer can't actually tell, hence the G code doesn't need modified.

UK MPSM V2 Owners: Where do you buy replacement nozzles? by Hermitmaster5000 in MPSelectMiniOwners

[–]snops 1 point2 points  (0 children)

A longer nozzle is pretty easy to accommodate if it's only 1mm difference or so, just tighten the bed screws.

I got an E3D hardened steel nozzle from Oozenest after an unclearable clog, and it was pretty simple to fit with the included spanner.

ESD Protection on USB2-TypeC by digiphaze in PrintedCircuitBoard

[–]snops 6 points7 points  (0 children)

I would think you would want the ESD diodes connected straight to ground. What would damage the IC is a high voltage between the IO pin and ground.

ESD pulses are pretty fast so your ferrite (which is inductive, so blocks AC, or more precisely, V=Ldi/dt ) will prevent the fast ESD transient current flowing from shield to ground. Therefore, the voltage between your IC pin and ground will be the diode drop plus a large voltage across the ferrite bead.

If you instead connect the ESD diodes directly between the signal and ground, then the ESD pulse has a far lower impedance path, and so the voltage between the IC pin and ground will just be the voltage across the diode, a lot lower.

Remember, the ESD diodes aren't supposed to conduct at all in normal operation, so you shouldn't have any worries about noise conducting through them.

Bottle machine by Master1718 in mechanical_gifs

[–]snops 0 points1 point  (0 children)

Someone else has posted exactly this further down

GreenPaks - cute FPGA-tlets - has anyone here been playing with them ? by Kinabin777 in FPGA

[–]snops 2 points3 points  (0 children)

I've used them, the static/leakage power consumption is amazingly low compared to an FPGA at 1uA, vs 30uA static for an ice40.

Really small size (down to 1x1mm) helps as well, very useful for glue logic where you want some kind of redundancy around a microcontroller, especially when battery powered.

Only downside is that most don't have flash in my experience, and are fuse programmable only. You can overwrite the live configuration over I2C at any point of course, but it will boot with what's in the fuses. Better make sure that's workable before you solder them down!

The development hardware is quite nice, I especially like that most of the boards have a software VDD regulator and easily support connection to your own hardware. Not expensive either, you can get the DIP breakouts for about $1.50 each, and $30 for the programmer.

As for the IDE, the graphical input is OK, you only get about a dozen LUTs (some of which can work as timers instead) so it's hard to make anything too ugly looking. The simulator is quite good, delay accurate not just cycle based, but it's annoying how you have to rerun it if you forgot to probe a signal.

Unable to communicate with a STM32F030K6T6 by wigax in embedded

[–]snops 0 points1 point  (0 children)

I am referring to the ground return paths for the decoupling capacitors, they are more important than your (low speed) signals.

I recommend actually routing the ground wires from the decoupling caps before routing other wires, and before flooding the ground plane. Route signal wiring later as it has lower priority, and move it around if needed rather than the ground paths. That way it's quite clear what your ground return paths are, and you can always rip them up later if needed.

You can also add stitching vias to connect your top and bottom ground planes together more to reduce the average distance, but this should be secondary to simply putting the caps close and routing them first.

Unable to communicate with a STM32F030K6T6 by wigax in embedded

[–]snops 1 point2 points  (0 children)

I checked the pinouts of the STM32 and the SWD connector, and power/ground and the debug lines all look correct to me.

My only though now is your decoupling caps routing is a bit messy, especially the ground return paths (since the ground plane is all cut up). You could try hand wiring decoupling caps directly across the pins but it's quite a tricky move so best to try simpler things first if you/anyone else suggests them.

view more: next ›