For the PIR sensor, the LDO regulator datasheet doesn't spec the minimum input voltage (Terrible, I say). I measured +3.3 out with my DMM, but that doesn't tell the whole story, so I would need to put a scope on it to be sure it's stable.
For the RasPi, the datasheet says we can run down to 3.5V and still get 3.3V reliably. So that explains why I never had any crashes, etc. Later today I will get the supply fixed back to +5V and see what happens. On Friday, November 22, 2024 at 8:11:33 AM UTC-8 Instrument Resources of America wrote: > Having only a 1/2V of headroom is not good. I'm surprised that you're > getting your 3.3V. Anything else operating from that 5V supply could be > real iffy. > > Ira > > > > On 11/21/2024 10:50 PM, gregebert wrote: > > So I checked my supply voltages, and that opened an unexpected can of > worms. The PIR sensor has it's own onboard linear regulator, and it's > pumping-out the expected 3.3VDC. The weird thing is the main 5V supply was > only putting out 3.8V. Despite that, the Raspberry Pi also had the correct > internal 3.3V supply (it also has it's own onboard supply). > > So, the first mystery is why a DCDC converter rated for 1amp, and > typically supplying 400mA conked-out when it's not getting warm or > overloaded. I confirmed the RasPi typically uses around 200mA, and > occasionally peaks around 280mA. > > I have to dig further into the regulators on the RasPi and PIR sensor to > understand why they still produce 3.3V when their input is way-below > 5.0VDC. I'm glad that they do, but I want to confirm why. > > I'll see what I have laying around for replacing the 5V DCDC converter, > and if they beefier ones I have will fit on the PCB. > > Once I get this thing back together, I'll see if the PIR sensor is back to > normal. I have some replacement PIR sensors on the way. > > Why the DCDC converter failed is another mystery; I use these on all my > projects, and seeing one fail is disturbing, especially because many of my > gizmos dont have onboard A/D converters to monitor the power supplies. > > On Thursday, November 21, 2024 at 5:08:19 PM UTC-8 Max Di Noi wrote: > >> I had that problem once and it was due to a faulty capacitor on the high >> voltage power supply creating instability on the HV circuitry and affecting >> the PIR circuitry, which was odd as that itself had its own capacitors >> located close to the chip and the main power supply had plenty of >> stabilised power. >> >> Now I'm trying to stabilise a microwave motion sensor that I designed >> based on one of those commercially available. It's embedded in the pcb, >> works OK but I need to figure out how to calibrate it more easily. It >> depends on temperature and material of the pcb. I purchased a frequency >> receiver up to 6gHz and I can see the signal on the screen. So that's a >> good start! Sorry, got sidetracked, slightly off topic :-) >> >> -------- Original message -------- >> From: newxito <[email protected]> >> Date: 21/11/2024 17:04 (GMT+00:00) >> To: neonixie-l <[email protected]> >> Subject: [neonixie-l] Re: PIR sensor got very sensitive >> >> Maybe you have to clean the trimmer resistors or there is a little bug >> inside, I had that problem but it was with an outside PIR :-) >> >> gregebert schrieb am Donnerstag, 21. November 2024 um 07:50:38 UTC+1: >> >>> Here's a strange story....a few weeks ago, I noticed my 7971 clock was >>> running a lot more than it was a few years ago. After some experimenting, I >>> found out the PIR sensor is getting a lot of false triggers (no movement in >>> room, even covering-up the sensor didn't keep it off). Turning-back the >>> sensitivity 1/4 turn did nothing, so I put it at minimum sensitivity and it >>> seems to stop the false triggering. It still detects motion. >>> >>> Anyone else see this happen ? The sensor has been in-use for about 6 >>> years; it's one of those cheap 5V units that cost about 1 USD and worked >>> fine for many years. >>> >>> >>> -- >> You received this message because you are subscribed to the Google Groups >> "neonixie-l" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion, visit >> https://groups.google.com/d/msgid/neonixie-l/f054d906-771b-4e73-9593-53c3e95e56f5n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/neonixie-l/f054d906-771b-4e73-9593-53c3e95e56f5n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > > To view this discussion, visit > https://groups.google.com/d/msgid/neonixie-l/340ffb9a-b775-4a49-b1ae-0fde15e3ac6bn%40googlegroups.com > > <https://groups.google.com/d/msgid/neonixie-l/340ffb9a-b775-4a49-b1ae-0fde15e3ac6bn%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. 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