You have a messed up power supply. It is putting tons of noise on the power bus. Take a sensitive high impedance audio amplifier and connect it across Vcc and ground. Listen. It should be very quiet if it's correct. I bet yours has all sorts of hash in it. That hash will cause all sorts of weird circuit behavior.
On Friday, November 22, 2024 at 12:58:46 PM UTC-5 gregebert wrote: > 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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