Adafruit PIR: Reducing (Tx + Ti) to less than 1 second

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KobeJohn
 
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Adafruit PIR: Reducing (Tx + Ti) to less than 1 second

Post by KobeJohn »

Is there some alternative way a newbie with a regular soldering iron (round tip) can reduce Tx and Ti on the Adafruit PIR? I think I'm likely to break my PIR with the method linked by Adafruit here.

I have 3 Adafruit PIR sensors that I'm using to make a motion-aware toy for the neighborhood kids. I need to catch movement with low lag so I'm monitoring it in non-retriggering mode. Maybe I should have gone with different sensors but I would like to work with what I have for now.

For the low lag time I need (Tx + Ti < ~1 second). I reduced the Tx POT to minimum which the information here suggests will reduce Tx to ~2.5 seconds. Actually my 3 sensors have a minimum Tx of 4s, 4s and 7s (This is Tx, not (Tx + Ti) since I have timed the high period). That means (Tx + Ti) is at minimum 5-6s for the sensors I have. In any case, it's too long for my application and any ideas would be appreciated.

By the way thanks for all the learning information on the site. It really does help a lot for people who are not well versed in the electronics industry.

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adafruit_support_bill
 
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Re: Adafruit PIR: Reducing (Tx + Ti) to less than 1 second

Post by adafruit_support_bill »

I don't know of any way that does not involve soldering and/or de-soldering of the surface mount resistors. You do need a steady hand and a fairly fine tip on your soldering iron. But the components involved (resistors) are not especially delicate.

KobeJohn
 
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Re: Adafruit PIR: Reducing (Tx + Ti) to less than 1 second

Post by KobeJohn »

Thank you for the reply. I threw a few more yen on the tool pile to pick up a t18-br02 (0.2mm) tip. I'm going to use filed chopsticks for poor mans ESD tweezers (like these). We shall see how steady my hand is and whether or not I can scrounge up small smd resistors from an old computer or something.

Getting to the details of changing the parts, it looks like either I don't know how to read these boards, or the actual PIR doesn't match up with the information on the page. Could you double check and post the specified values and locations of Tx (R and C) and Ti (R and C)?

Regarding Tx:
  • On mine, R10 is 202/2k when the page says it should be 103/10k (Suspect R10 highlighted in red in the attachment)
  • If I try to interpret the traces under the printed lines, I believe R13 is connected to the Tx POT and is indeed a 103/10k. Is that an error on the explanation page? (R13 is highlighted in yellow in the attachment).
  • On mine, C6 is unlabeled
  • Without C6, I can't confirm the calculation. However, assuming the cap value is accurate, to get the ~4s Tx that I have, there would need to be about a 20k resistor instead of 10k and definitely not 2k. I have to assume the (cap + resistor) are off by a factor of 100% to get double the specified Tx, or perhaps the Time POT does not actually zero-out. In any case, something is off.
Regarding Ti:
  • On mine, R9 is 105 (1M???). The page doesn't provide any Ti information for the Adafruit sensor so I can't confirm whether this is sane or not. It doesn't sound right though. (Suspect R9 is highlighted in red in the attachment)
  • The explanation page doesn't mention specified R or C for the adafruit PIR so I'm not sure what they should be.
Adafruit PIR.JPG
Adafruit PIR.JPG (303.08 KiB) Viewed 380 times

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adafruit_support_bill
 
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Re: Adafruit PIR: Reducing (Tx + Ti) to less than 1 second

Post by adafruit_support_bill »

It looks like your board is quite different from the one pictured. Have you experimented with the trim-pots on the top edge of the board? These may provide the adjustment you need.

We don't manufacture these in-house, so we don't have the schematics for them.

KobeJohn
 
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Re: Adafruit PIR: Reducing (Tx + Ti) to less than 1 second

Post by KobeJohn »

It looks like your board is quite different from the one pictured.
There are 2 pictures of "older/other" PIRs on that page that indicate what other PIRs people might have. There are 3 pictures of the Adafruit PIR on that page which is what I have and as far as I can tell those pictures match the picture I uploaded exactly.

----------------
Have you experimented with the trim-pots on the top edge of the board?
From my first post:
I reduced the Tx POT to minimum which the information here suggests will reduce Tx to ~2.5 seconds.
----------------
We don't manufacture these in-house, so we don't have the schematics for them.
I see. However, I hope you can still help me. The discussion on that page sounds like it is referring specifically to the Adafruit PIR because it includes the trim POT that the Adafruit PIR has in the calculations. The "older/other" one does not have the trim POT. This suggests that someone at Adafruit has figured this out before.

Perhaps you or the person that made the guide would be able to update it with the correct information or tell me where I have gone wrong?

If not, perhaps that part of the guide should have a note added to indicate that it is inaccurate?

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adafruit_support_bill
 
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Re: Adafruit PIR: Reducing (Tx + Ti) to less than 1 second

Post by adafruit_support_bill »

The page from Kieth's Electronics Blog that you referenced in your post was not written by Adafruit and all the photos on that page show a device with no trim pots.

Since at least one of the trim-pots on your sensor appears to be wired in series with a fixed resistor, you can try just shorting the fixed resistor to lower the overall resistance.

KobeJohn
 
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Re: Adafruit PIR: Reducing (Tx + Ti) to less than 1 second

Post by KobeJohn »

adafruit_support_bill wrote:The page from Kieth's Electronics Blog that you referenced in your post was not written by Adafruit and all the photos on that page show a device with no trim pots.

Since at least one of the trim-pots on your sensor appears to be wired in series with a fixed resistor, you can try just shorting the fixed resistor to lower the overall resistance.
I see where our miscommunication is. I'm referring to the Adafruit learning page that I also linked in the first post. Most of the discussion and calculations on the Adafruit page I linked are specifically referring to the PIR that Adafruit sells. The Adafruit page is what I have been intending to discuss in this whole thread and the information on the Adafruit page is what I would like to get updated/corrected information on. The page from Kieth's Electronics Blog was only referenced for the technique, not the PIR data.

If getting updated/corrected information on the Adafruit PIR is impossible, I was recommending that the Adafruit page be updated to note that the component labeling information may not be accurate so that other people using the page with little experience like me don't break their sensors when trying to modify them.

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