Battery powered PIR

[Mrlynx]

@m26872 I am looking at xc6206 and tc2117 that have a low quiescent current and a dropout of 50-100 mV at low currents.

[Yveaux]

@therik I recently observed the same behaviour with a step-up regulator based on a 2108A.
The strange thing is that the sensor behaves erratic when powered from 2 fresh AA alkaline batteries (approx. 3.2V input to the regulator) but works just fine when powered by some older AA alkaline batteries (approx. 2.6V input).
I quickly inspected the output of the regulator with a scope, but saw no clear differences between the two. Maybe the output was less stable at 3.2V input.
Next I'll try using a diode to lower the voltage a little, either before or after the regulator.

[riaan003]

I am trying to figure out if running this modification from 3 AAs at 4.5V will work (it is for a setup with a attiny85 that I want to run from 4.5 down to 3.3v - it currently works well from 5 down to 4.5 with exactly the erratic behaviour explained above from about 4.4v and down). When looking at the datasheet for the BIS0001 then it seems like it will fine? What am I missing? :)

[therik]

A couple of questions.

1. Did you remove the voltage regulator from the PIR?
   a. if not, I would suspect that the voltage regulator on the PIR drops out and cannot supply the voltage for the PIR IC below 4V5.
2. Where do you derive the power for the PIR?
   a. If it is from the µC, the µC may be adding noise on the voltage supply to the PIR and with the PIR voltage regulator removed the supply voltage may be too noisy.

[riaan003]

The regulator was not removed yet, no, the behaviour was with my unmodified sensor. I have actually now started looking at an alternative power setup so that i can use this mod at 3.3v and drop the requiment for it to run from 4.5v (which was based on running it upregulated from 3 AAs with an attiny85 woken up from sleep mode - which worked well and consumed ~0.1mA overall). Back to the drawing board :)

[Igor Katkov]

How did you produce that nice ripple charts? Oscilloscope connected to a computer? What is the model?

[Haakon]

Thanks for sharing, @therik. Where can I get the high-ripple-rejection-ratio regulator you are describing? I cannot find an FT531IA on Ebay. (Or if therik is no longer following the topic: Anyone else know a specific regulator I gan get from Ebay?)

Thanks in advance.

[LastSamurai]

It's still on aliexpress. Could a AMS1117 work too though? It's ripple rejection isn't bad for what I have read. Although I don't get the part of the specs.. if you use a fixed version do you still need a capacitor on the GND (adj) pin for the ripple rejection?

[Haakon]

Thanks, @LastSamurai! I have ordered a few to try them out. (Not sure about the question about AMS1117, hopefully there are someone here who are.)

[n1ck1355]

Hi :)
does anyone know where i actually find the FT531IA? on aliexpress there are only FT531EA with output of 2.5V :(