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Friend of mine wants to increase the time ON for a light with this motion detector. Right now it only shines for about 20 seconds and he would like about 2-4 minutes .Theirs no adjustment but I'm thinking that if I increase the value of R7 that should do the trick.
Now from what I understand the 56nF cap is charged by pin 4 then when theirs a trigger C3 discharges across R7 into pin 3 keeping pin 2(Vo) High for a period of time until C3 is discharged.
Am I correct in my thinking?
https://cdn-learn.adafruit.com/assets/assets/000/010/133/original/BISS0001.pdf -
Looks like you'll want to change R10 or C6.
From your link:
Tx: time duration during which the output (Vo) remains high after triggering.
Tx ~= 24576 x R10 x C6 -
For some reason my first post didn't include my attachment.What am i doing wrong?
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Can't be sure just looking the photo. But check if R7 terminal is at same node as Pin 4 and C3.
Anyway, for me it also looks possible that it's going to R8, and the schematics doesn't show this connection.
See the orange circle in attached image. It looks like there is a track right in the middle of the circle.Looks like you'll want to change R10 or C6.
@Kasper, from picture posted later it seem that PCB and Schematics have different annotation.
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Can't be sure just looking the photo. But check if R7 terminal is at same node as Pin 4 and C3.
Anyway, for me it also looks possible that it's going to R8, and the schematics doesn't show this connection.
See the orange circle in attached image. It looks like there is a track right in the middle of the circle.
Just a badly cleaned board. See attachment
The first problem I'm having for some reason not all of my post is being uploaded. weird.
What I'm having trouble with is at pin 3 and pin4 the values marked on the photo would give the right time . But the true values are 47K at pin 3 .It's Marked Code is 473 and measures close to 47K .
At pin 4 my measurement has to be wrong for I get conflicting values at different test frequencies.At 100hz C3 is 6uF . 1kHz is 510nF ,10kHz is 30nF , 100kHz is 10nF
I guess I'll have to pull the cap and test it then .
The other problem is the formula given on the data sheet doesn't explain the magnitude of each value . Is the time in seconds ,mili seconds ,micro seconds ? Is the capacitor in nF ,uF ,F ? Is the resistor Kohms ,Ohms ? I put the values in the equation because they just happen to work but actual values don't make any sense.
Also the data sheet refers to a "timing chart" . Wheres the timing chart on the data sheet ?
Sorry about confusing everyone but this is frustrating when data sheets are crappy.
On a happy note I'm really pleased with my new microscope.
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Using the formula, 47k/10nF is 11.6sec, 47k/22nF is 25sec so you likely have a 22nF there.
47k 100nF gives 115 sec. almost 2 minutes. I see even 470k 10nF used, or a 1MEG trimpot.
I would just add a 100nF on top and see what you get. Or 220k-470k resistor instead of the 47k. -
Looks like you'll want to change R10 or C6.
@Kasper, from picture posted later it seem that PCB and Schematics have different annotation.
Yes, it looks like R10 and C6 in datasheet = R7 and C3 on PCB.What I'm having trouble with is at pin 3 and pin4 the values marked on the photo would give the right time . But the true values are 47K at pin 3 .It's Marked Code is 473 and measures close to 47K .
At pin 4 my measurement has to be wrong for I get conflicting values at different test frequencies.At 100hz C3 is 6uF . 1kHz is 510nF ,10kHz is 30nF , 100kHz is 10nF
I guess I'll have to pull the cap and test it then .
The other problem is the formula given on the data sheet doesn't explain the magnitude of each value . Is the time in seconds ,mili seconds ,micro seconds ? Is the capacitor in nF ,uF ,F ? Is the resistor Kohms ,Ohms ? I put the values in the equation because they just happen to work but actual values don't make any sense.
Also the data sheet refers to a "timing chart" . Wheres the timing chart on the data sheet ?
Sorry about confusing everyone but this is frustrating when data sheets are crappy.
On a happy note I'm really pleased with my new microscope.
I would assume the units are seconds, ohms and farads but that doesn't really matter, you can test and figure it out. Replace the cap with one about 10x more farads (since you want 10x more delay) and test it. If you set it in non-retriggerable mode it should be easier to get accurate timing measurements during your test.
To test C3 it seems you'll need to remove it but you could skip all that and just add the cap you think you need based on the formula and then test it. Add a capacitor between south side of R7 and south side of C3 or on top of C3. Either way it should be in parallel with C3 which would add to the capacitance of C3 so your new formula would be:
C3b: cap added in parallel with C3
Tx ~= 24576 x R7 x (C3 + C3b)
Since C3b should be 10x bigger than C3, you could remove C3 from the equation without loosing much accuracy.
Tx ~~= 24576 x R7 x C3b
I think when they reference timing chart they mean the 2 images titled '...waveform'