Was wondering if anyone could either make for me or point me in the right direction for components for a motion or proximity sensing led setup. More specifically, I had a last minute thought for that 10x10 show and don’t want to have to worry about whether or not there are any usb slots left open so need a real simple circuit supplied by 9v battery that will have a single bright led turn on for a few seconds whenever someone walks by. Hoping to keep it as small as possible to keep it hidden and self contained within the 10x10(x4). I’m guessing it would just be a motion or proximity sensor/switch, the led battery and resistor or 2? idk
Bear with me here, I intentionally didn’t become an EE because I can’t make the mental transition from a wiring schematic to real world objects. Is my re-drawn version correct? Also, the 3k to 10k resistor - is that just anything within that range will work or is it dependent on the specs of the actual led? Please forgive my ignorance…
There’s one too few resistors in this schematic. 3k-10k is not critical.
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You’re missing the resistor on the LED between it and the transistor in your translated drawing.
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It got lost in translation… * sad & horrible rimshot * - I got all confused and figured the resistor was “shorthand” for the actual LED. It doesn’t help that schematically the PIR looks just like a surface mount led (other than an extra lead), but again… I blame my brain. Moving forward, I just picked up the PIR, transistor and a couple different (non-red) leds - so just gotta dust off an old EE textbook and figure out the resistors. Thank you both so much for your help!!!
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Make sure you use the Adafruit PIR or equivalent, since that one takes 9V but not all of them do (or make sure yours does)
The schematic symbol for the PIR is just a thing I drew that kinda looks like a PIR sensor. Nothing magical about it–
Regarding the EE book, that should not be necessary, just plug in the forward voltage of the diode, the desired LED current, and do that calculation. Pick the next higher standard value. Feel free to post your results here to check your work.
I’d use a simple 9 volt Vellman sound to light solder kit from Tanner. Just change the input from microphone to IR somehow and connect to led, depending on the strip power should be fine. not fancy but …
I did make sure to get the adafruit pir and 1 clear and 1 uv led - i’m not sure which way to go yet with that. The led’s were just thrown in a big so I spent awhile last night trying to figure out what the specs generally are for these (they’re both 5mm). Then lit them up with just the 9v battery and tried both a 300 ohm and 275 ohm resistor. Works well so far - now need to add the transistor, pir and 2nd resistor - which is the only part I’m not clear on (the resistor value i mean), but can probably fumble my way through. I hate all of this so much - it’s beginning to pique my interest… I need another interest about as much as I need another (insert thing I don’t need anymore of here).
If you use a multimeter and measure the voltage across the LED with your battery and resistor, that should give you a good measure of Vf. Almost any LED can handle 20mA max, so that’s usually the max I design for unless I have more info.
Just a safety note about the UV LEDs though, it would probably be appropriate to design it so that a viewer cannot look directly into it. It may not look very bright, but as it’s partially invisible it can damage your eyes under certain conditions.
Yah - the led will be completely blocked from direct viewing regardless of color - I’m using it for indirect lighting. From what I read last night, it looked like the Vf for the clear led was between 3.0 -3.6V and the UV was 3.5V and I used 20mA. If I’m only going to have the led go off for 10 secs (I think that was the minimum amount of time the PIR does) I might try bumping it up 25 or 30 mA if I’m not getting the effect I need - I should’ve bought a handful of them when I was at tanner so I could pop a few. On that 2nd resistor - can I just split the difference and throw in a 6k or 7k and be done with it?
Thanks for info on multimeter! - measuring now…
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…Both measured within a few 1/100s of 3.3
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Yes that’s fine