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by emma1997
Sat Nov 16, 2019 2:55 am
Forum: Automation, sensing and robotics
Topic: 12v DC proximity detector for use on truck (2-3 feet range)
Replies: 12
Views: 233

Re: 12v DC proximity detector for use on truck (2-3 feet range)

If you are talking about the cheap Chinese 'radar' modules https://www.ebay.com/itm/RCWL-0516-Switch-Microwave-Radar-Sensor-Module-Induction-Human-Board-Detector-TR/352666551849?hash=item521c908629:g:HWEAAOSws3lc3ln8 , first they are not radar at all but sloppy 3ghz doppler detectors. Second they ca...
by emma1997
Thu Nov 14, 2019 7:58 pm
Forum: Advanced users
Topic: Is it possible for RaspberryPi 3 B+ to power a 6V device
Replies: 14
Views: 419

Re: Is it possible for RaspberryPi 3 B+ to power a 6V device

Yes, that seems to be the case, at least according to theory. However in my experience that parasitic diode does not seem to cause a problem emulating keys in a battery operated remote. Maybe the low voltage doesn't interfering with such a small DC offset since the key scan signal is low. All I can ...
by emma1997
Thu Nov 14, 2019 4:20 pm
Forum: Advanced users
Topic: Is it possible for RaspberryPi 3 B+ to power a 6V device
Replies: 14
Views: 419

Re: Is it possible for RaspberryPi 3 B+ to power a 6V device

Reviewing posts I see now that as usual you were more on top of things. Yes, the best remotes do use those tact type, specially if there's only one or two. Elastomer don't shine until number of buttons gets up there like the one in todays other thread. BTW for matrix type (probably not the case here...
by emma1997
Thu Nov 14, 2019 3:31 pm
Forum: General discussion
Topic: Fixing the Pi 4 usb C issue by hand
Replies: 39
Views: 7057

Re: Fixing the Pi 4 usb C issue by hand

I doubt any company would create an adaptor for commercial sale as it would probably be too costly given the small market for such a board What do you mean 'small market'? There have to be at least 3 individuals here in the US alone desperate for such a solution. Considering design and tooling shou...
by emma1997
Thu Nov 14, 2019 3:11 pm
Forum: Advanced users
Topic: Is it possible for RaspberryPi 3 B+ to power a 6V device
Replies: 14
Views: 419

Re: Is it possible for RaspberryPi 3 B+ to power a 6V device

In my experience the 4pin so call 'tact' buttons are less common for this type device. Cheap remotes usually have elastomer keypads with contacts being PCB traces like in todays other thread on the subject. We don't know exactly what type here but probably the same. A good photo like the one in the ...
by emma1997
Thu Nov 14, 2019 2:58 pm
Forum: Beginners
Topic: Operating a 433mhz remote control with a Raspberry
Replies: 8
Views: 225

Re: Operating a 433mhz remote control with a Raspberry

I can't figure out how to mimic a button press with gpio pins. Has anybody already tried (and succeeded, maybe) this? Many have (even recently on this same website) as a quick search would have found: https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=256738&p=1565688#p1565688 . That was right...
by emma1997
Thu Nov 14, 2019 2:47 pm
Forum: Advanced users
Topic: Is it possible for RaspberryPi 3 B+ to power a 6V device
Replies: 14
Views: 419

Re: Is it possible for RaspberryPi 3 B+ to power a 6V device

Optoisolators are an excellent solution where high voltages or long wires are involved. I would not be concerned with sensitivity as the output current is very low, microamp or nanoamp range. I've been able to use as high as 10k to drive the LED with 3n28 which is about the crummiest/cheapest there ...
by emma1997
Wed Nov 13, 2019 8:16 pm
Forum: General discussion
Topic: New Pi 4B v1.2?
Replies: 28
Views: 1975

Re: New Pi 4B v1.2?

Not surprising to me at all. I think RPF/RPT may want to 'flush the pipes' to avoid Osbourne Effect. I know I wouldn't mind treading water for a month or two, maybe even longer, in order to get latest and greatest.
by emma1997
Wed Nov 13, 2019 8:02 pm
Forum: Off topic discussion
Topic: What dictates the accuracy of a gps module?
Replies: 8
Views: 272

Re: What dictates the accuracy of a gps module?

I use lots of Neo6m too because they are cheap as chips. Specially just the chip itself which does function with nothing more than piece of wire antenna. As little as $2 for chip and $3 for PCB with chip, free SH from China. They also do an excellent job compared to older brands. Aside from weather,...
by emma1997
Wed Nov 13, 2019 6:52 pm
Forum: Advanced users
Topic: Is it possible for RaspberryPi 3 B+ to power a 6V device
Replies: 14
Views: 419

Re: Is it possible for RaspberryPi 3 B+ to power a 6V device

What i want to connect is remote for my garage door and simulate key press on remote using raspberry pi relay or GPIO pins, Best way to activate keys is with MOSFETs like 2n7002. Cheap and available everywhere. Old tech bipolar transistors (ie 2n3904) also work but require extra components. The poi...
by emma1997
Tue Nov 12, 2019 5:57 pm
Forum: General discussion
Topic: Raspberry Pi 3 is getting hot even kept idle
Replies: 20
Views: 489

Re: Raspberry Pi 3 is getting hot even kept idle

I was asking about protection diode maximum forward bias not GPIO drive current. However if there are no diodes at all that does, if true, explain a lot of strange readings by myself and others on the internet regarding input voltage tolerance. Mostly I was wondering if this is documented anywhere a...
by emma1997
Tue Nov 12, 2019 5:06 pm
Forum: General discussion
Topic: Raspberry Pi 3 is getting hot even kept idle
Replies: 20
Views: 489

Re: Raspberry Pi 3 is getting hot even kept idle

Thank you for that link mahjongg. I don't know how I missed it all this time. Specially since it's listed as sticky but apparently not in an area I've ever visited. For CMOS devices there is often specified a typical latchup current limit (usually microamps) and also maximum forward current for clam...
by emma1997
Tue Nov 12, 2019 1:05 am
Forum: Troubleshooting
Topic: Cannot read pin if used.
Replies: 11
Views: 235

Re: Cannot read pin if used.

I don't see any pic with 470 to ground but just replacing with 10k is not a good solution. If so then it's probably right on the edge and could stop working if temperature increases 1 degree. As mentioned, you could either add a SERIES resistor between base and pin or just rewire that BC337 as commo...
by emma1997
Tue Nov 12, 2019 12:52 am
Forum: Off topic discussion
Topic: Logic NOPE gate IC
Replies: 15
Views: 437

Re: Logic NOPE gate IC

I though humor was frowned upon here. Lol. Actually I found a few (at least some members of AHCT family) make YEP gate (always high regardless of input) in that state.
by emma1997
Tue Nov 12, 2019 12:10 am
Forum: Troubleshooting
Topic: Cannot read pin if used.
Replies: 11
Views: 235

Re: Cannot read pin if used.

If that was a MOS type transistor (2n7002) no resistor is needed. A bipolar transistor (BJT) in follower mode no resistor is needed. In this case, common emitter BJT, a 1k or so between base and pin would be a good idea. However IME not likely to 'damage' without it. I'm also convinced LED by itself...
by emma1997
Sat Nov 09, 2019 10:48 pm
Forum: Troubleshooting
Topic: 2x failed Pi 4's
Replies: 22
Views: 1000

Re: 2x failed Pi 4's

Scope was a 60ghz Lecroy so able to catch quite small pulses. Typically picosecond or less. I agree on the timeframe. In a previous life working in wafer fab I learned that things can happen very fast. Depending on type of abuse it's possible to damage a junction quickly. Not so much in cases of hea...
by emma1997
Sat Nov 09, 2019 3:57 pm
Forum: Troubleshooting
Topic: 2x failed Pi 4's
Replies: 22
Views: 1000

Re: 2x failed Pi 4's

If PSU is suspect that can be checked with a scope, even $10 Ebay one. Poorly designed switchers are susceptible to a sometimes fatal startup-overvoltage design flaw. One of my recent buck prototypes showed a 21v pulse on the 5v rail every time powered up. Yikes! Unlikely to damage anything due to d...
by emma1997
Sat Nov 09, 2019 5:20 am
Forum: General discussion
Topic: How to Wire 5V and Battery
Replies: 25
Views: 547

Re: How to Wire 5V and Battery

Lol. You confused me with a post from your friend Lewis. ( where did I leave those meds.. :) ) His comments made no sense. If you keep that battery fully charged, above 4v, which is a good idea anyway, it should work. Not something I would use for Mars Lander or medical machine but can be a fun proj...
by emma1997
Sat Nov 09, 2019 3:04 am
Forum: General discussion
Topic: How to Wire 5V and Battery
Replies: 25
Views: 547

Re: How to Wire 5V and Battery

Sorry, Lewis. Wrong on both counts. Two batteries can be connected together, either in series or parallel. If connected in series, the voltage out is the sum of the individual batteries (i. e, two 3.7V 2A batteries in parallel produce 7.4V output at 2A; two 3.7V 2A batteries in series produce 3.7V ...
by emma1997
Thu Nov 07, 2019 9:50 pm
Forum: Beginners
Topic: Does the GPIO send current when its not activated?
Replies: 7
Views: 174

Re: Does the GPIO send current when its not activated?

Thanks again. I must say I've learned a lot about technical aspects here from you and other Santas Helpers. You know who you are! :)
by emma1997
Thu Nov 07, 2019 9:42 pm
Forum: Troubleshooting
Topic: RPi 4 doesn't boot: ACT LED remains dark
Replies: 14
Views: 423

Re: RPi 4 doesn't boot: ACT LED remains dark

The only time I got same symptoms (no green LED) with a good card was when wrong pin was connected to the enable input of a PSU (UART instead of digital output). So an unstable DC can do this even though measured 5v with meter. Scope showed the real problem. Don't seem possible in this case though. ...
by emma1997
Thu Nov 07, 2019 9:19 pm
Forum: Beginners
Topic: Does the GPIO send current when its not activated?
Replies: 7
Views: 174

Re: Does the GPIO send current when its not activated?

GPIO 0-8 have weak pull-ups to 3V3 enabled at power-on. The other GPIO have weak pull-downs to ground enabled. In addition GPIO 2 and 3 have hard wired 1k8 resistors to 3V3 on board. Thank you for that. Wonderfully simple summary. I came to similar conclusion but only after half hour with DMM. I ha...
by emma1997
Thu Nov 07, 2019 8:50 pm
Forum: Troubleshooting
Topic: Problems with power on Pi 4
Replies: 11
Views: 327

Re: Problems with power on Pi 4

QC is a bit better compared to the Chinese cheepies but having purchased thousands of these for various clients last few years from both venues I found no big difference in reliability. Maybe single digit percent difference at most for 5x the cost. Mission critical applications then yes, but even th...
by emma1997
Thu Nov 07, 2019 8:24 pm
Forum: Troubleshooting
Topic: Problems with power on Pi 4
Replies: 11
Views: 327

Re: Problems with power on Pi 4

Since this is going thru a DC DC converter and a set of batteries, I wanted the extra (although tiny) bit of built in protection as opposed to just jamming the power unprotected into the GPIO AFAIK unlike previous models Pi4 does not have any 5v protection. 5v inputs&outputs are all directly connec...
by emma1997
Thu Nov 07, 2019 7:36 pm
Forum: Beginners
Topic: Does the GPIO send current when its not activated?
Replies: 7
Views: 174

Re: Does the GPIO send current when its not activated?

Welcome to the forum. As an EE I also find the subject of electrical characteristics and IO interesting. Not likely a Pi was fried with 330ohm resistor. There is lots of fear mongering on this subject but IMO Pi are very rugged devices. Maybe not up to Arduino but not far from it. Dim LED syndrome i...

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