Classic Circuits You Should Know: Light/Dark Detector
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- Опубліковано 9 лип 2024
- Classic Circuits You Should Know: Light/Dark Detector
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I would think swapping the resistors in the divider would do it? Nice stuff we need more like this. Thanks for the video!
thank you so much for your tutorials!
Thank you for this. Another outstanding demonstration and explanation.👍👍
Dear Sirj ust a bright Thank You very much for all of your very interesting electronic projects! It‘s so easy to understand the way you explain all that to me/to us👍🏼 I hope you can go on! Boris🇨🇭
Really nice, man! Thanks a lot! 😊
Thanks buddy, i took this one and changed it a little for my garden lights, for ages i was getting the ones you spike in the ground but they were crappy so i would modify them, i just made my own using the Rotating colours LED's and marbles to refract the light and a stack of D-cells in a coffee jar, they will last about 6 months now, lol
O love this One! Thanks Sir!
Swap 10k and LDR. In that case when LDR get bright whough trasistor base voltage is rising to point (0.6V + Uled) where led start to work. Also don't try to use this type of circuit for normal lamp. Use common emitter circuit for better switching caracteristics and lower power loss in transistor. For big current lamps darlington is needed for enough high hfe or drive relay.
Edit:
There also is broblem when changin 10k and LDR. if LDR go enough low resistance when bright then transistor Ib is going high because LDR is only limiting factor for led current.
Edit2:
Good idea usually to draw all chematics if you are doing some circuits. That help people to understands how it's really connected.
Grate video. I have a radio shack circuit/component test kit and I just built both circuits but it’s downfall is it doesn’t explain why it works and you have just explained it for me. I will go build each one again and possibly answer the question. My lucky day as I am just a rookie at electronics teaching myself but this is a great channel. Thanks for sharing Artie 👍👍👍
Nice job!
This series is great!
Swap the ldr and resistor above. Being me, i would put a trim pot to vary the sensitivity. Love the simplicity of this circuit.
Nice. Thanks for the lesson.
Switch LDR and 10k resistor.
*Good one!*
You explained that perfectly! Well done! Thanks!
No big deal, but I wonder how much current is flowing when the LED is off. I’m guessing it’s pretty minimal.
Thanks again!
very new to this but I would guess at swapping the LDR with the other voltage divider resistor
Great video as always, may I please ask you a question: could that LDR not also be replaced by a NTC Resistors, to detect heat?
Classic fun first transistor circuit. When you swap the resistors in the voltage divider it works the exact opposite way. This was one of the first things I breadboarded when I started learning electronics. I’ll tell you one thing it took me awhile to wrap my head around the simple component swap reversing the behavior, but it hooked me. Great video Paul.
I put this circuit together, and it worked to turn on when dark. When I switched the 10k and LDR the led would be one when light, but would not turn off when the LDR was dark, it would only dim.
Did I do something wrong?
@@felixcosty It's using transistor as voltage follower and not like switch. "Simple" solution tweak resistor values and swap led and transistor place. With this you have to use base resistor if ldr going too small value.
@@LimbaZero the question at the end of the video. I do not have the knowledge to form the right question this the best I can come up with. Does switching the LDR and 10K answer the Question?
And if so the circuit created works more like a dimmer switch, then and on off, instead of being the opposite of the original circuit. Was the question at the end of the video to be and on off switch, but on in daylight and off at night, this is wear it gets a bit confusing.
@@felixcosty yes. switching 10k and ldr is right answer.Current version of circuit is "dimmer" style. 10k and ldr set voltage for base and emitter is about 0.6v under that. This circuit wotk this way with leds because they have treshold voltage. if normal lamp is used then it's dimming it. When led is stating to take more current then voltage over 22k resistor is close to 10k then it start limit current for led.
thank you ,thank you ,thank you
Good man!
Thanks Paul.
Nice video!
Are you sure about the common collector, I think it is common emitter.
Kind regards
Answer :- i just goona add the LDR in series of LED . Hence in presence of light LDR resistance drops and current can easily pass through it and glow up the LED.❤❤
Swap the base resistor/ldr round, I don't use this circuit much as I tend to use a photo transistor coupled to a pnp Darlington, it doesn't trigger so early when the sun goes down.
An interesting variation would be to use a light sensitive transistor. Perhaps you could do one with one of those for comparison.
If the photo transistor feeds a Darlington that also works and with more current handling
Replacing NPN transistor, with a PNP one.
I had to increase my resister values by quite a lot to get this to work.
Im curious if this works the way it does because of electron flow or conventional flow?
cool circuit
swap the LED from the emiter to colector, so emitter directly goes on GND and from VCC to 22k to Anode and katode to colector ?
Good one Buddy!! Let go deeper with it? Using pot and relay for output?
yep yep
replace the 10k resistor with a resistor having resistance equal to ldrs normal resistance which was about 0.8k in your case so that there is equal voltage drop and the current takes the path to the transistor and to the led
Swap the LDR and the base bias resistor
Yes
@@learnelectronics That would have been my answer as well, all thanks to arduino and this channel. I've learned so much from this channel over the last year. Thanks Paul.
I actually surprised myself by building this without no schematic. I also built an h-bridge without a schematic.
Not sure about the 22K current limiting resistor? Should it not be more like 220R?
Like I said, i carefully chose those values to limit the current.
Hey Paul could you do a review on the new must tool scopemeter when it comes out soon on banggood. It's an upgrade from th MT8205...Because I was hoping it would be a good buy. Thanks.
P.s. swap it with the bais resistor so that during the day the bais is more positive and stays on...
Ill see if I can get one.
you are correct!
Why doesnt the current ALSO flow through the transistor when the LDR has low resistance? why only to ground?
Well, it does, but at a much smaller current, thus allowing a much smaller emitter current. Think of it as a voltage divider with the 10k from Vcc to midpoint, and the CDS cell AND the transistor's base to emitter resistance from midpoint to ground. When the resistance of the CDS goes low, it pulls the voltage at the midpoint low, giving less voltage (and less current) at the base.
I made a light pen for the c64 using one.
Its like you build a simple NOT gate .
Swap the resistors on the VTG divider
Swap the base bias resistor and LDR to create a dark/light detector.
Works a treat but energy efficient... not so much.
Wouldn’t using a PNP transistor (Base pulled high using a higher value resistor) Base biased to ground via LDR be more efficient?
Or is that why you are using a NPN transistor as a high side switch?
Just guessing - will have to look that one up...
Thanks for your insights, I appreciate your videos greatly.
Makes me stop and think.
Especially as most espouse digital solutions when I am often looking for simplest solutions.
der bender nice - as a low or high side switch?
turn it around, I'm just learning, so that is really a guess. will be looking forward to the answer
Yes
Is the voltage rating on LED's the same as the voltage drop across them? Your using a 12v power supply and it looks like your limiting current but not voltage across the LED.
If you limit the current then you are automatically also limiting the voltage on the diode, because the resistor will drop the excess voltage. If the current is within the rating of the led, you are good.
@@cosimo8046 Just for fun I created a circuit with an app called EveryCircuit that used a 12v supply and an Led connected in series with a 22K resistor. I had to turn the power supply up to 800 or 900 volts to fry the Led. That huge resistor really limits the current!
Juz use PNP bjt, it will work in reverse.
And LDR said let there be light!
I thought current flowed from negative to positive. Was I taught wrong 60 - 70 years ago?
no that is right neg to pos. in the far past they thought it was pos to neg.
reverse the base
Put the LED in parallel
like
Welcome to darken lab😂
Let there be light! - God
Let there be more light! - Pink Floyd
Answer: Flip the resistor and LDR.
Correct
Did something similar with PNP transistor, but my favorite is with an Op-amp.
@@captainpugwash4100 op-amp is best for setting acurate tripping point. Also common emitter circuit is better for lamps and relays.
Kids be like - This was easier in Minecraft - LOL