# COMMUNITY

### LDR Grid + Smartphone = ?

Hi, I've got an idea but I don't know what it can be used for, yet. Maybe you'll have some ideas for useful applications based on this concept. The idea is to make a grid of LDRs which fits the size of a smartphone/tablet screen, write some code which draws a similar grid on the screen (or just switch images of that grid) so that each LDR will be affected by the light (and color) provided by each cell from the screen.

Posted by nivini 2 years ago

### how to use LDR as a relay for RC car to increase voltage to motor

Hi there,  I would like to know more about how LDR's work, its quite difficult to source 3 volt relays in South Africa, so I had an Epiphany, why not use 2x  LDR 1x for Forward and 1x for Reverse on an RC car, I don't know much about how responsive the solution is, how many seconds or milliseconds delay  there is? Does it work like a switch?  would it be a viable option on an RC car? I'm sure this could apply to little 3 volt RC cars upwards, I know brushless is the way to go, however this would indeed be a great learning experience.  kindest Regards, Lee Reddy.

Posted by Leereddy1818 2 years ago

### Fitlight trainer using arduino

I want to make a fitlight trainer with arduino. I want to make it with leds and LDR ligtht sensors. A random light pops up and when you hover over the sensor it sets it to LOW and then another random light pops up and over and over. Can anyone help me with this idea? I have the code for one light: int LDR = 0;     //analog pin to which LDR is connected, here we set it to 0 so it means A0 int LDRValue = 0;      //that’s a variable to store LDR values int light_sensitivity = 20;    //This is the approx value of light surrounding your LDR void setup()   {     Serial.begin(9600);              pinMode(13, OUTPUT);      } void loop()   {     LDRValue = analogRead(LDR);      //reads the ldr’s value through LDR     Serial.println(LDRValue);       //prints the LDR values to serial monitor     delay(50);        //This is the speed by which LDR sends value to arduino     if (LDRValue > light_sensitivity)       {         digitalWrite(13, HIGH);       }     else       {         digitalWrite(13, LOW);       }   }

Posted by JordyK4 2 years ago

### Transistor help.... very basic, LDR/LED

I'm trying to make a very simple circuit to light an LED based on light from an LDR. I have all the components, it's a white LED, I'm using two AA batteries, and the LED glows brightly when I attach it to the batteries, but when I attach it to the LDR, it is either dim or dimmer due to the resistance... I'm sure I need to use a resistor for this... I have some assorted PNPs and NPN2222As... I've looked at a couple tutorials, but none of them seem to work... does anyone know how to do this without any (or as few as possible) other components? Thanks

Posted by perkinsb1024 11 years ago

### Does anyone do Automated Car Wash System by using Arduino with LDR?

I wish to know how am i able to write a program which i could control the water spraying, brushing and drying by using arduino.  My project is to use a laser pointer which will send the signal to the LDR and it will trigger the water to spray, brush and dry the toy car on the conveyor belt. Can anyone help me?? I'm a diploma student, and my supervisor is a mad man which who asked me to do such project which he doesn't know either.  The first image is how i think my circuit looks like The second image shows what i had done

Posted by ahchuan.ycc 3 years ago

### What to do with old robot? / Cybot

I found an old robot that was part of one of those 'build it yourself' magazine series. I was gonna eBay it but found there was actually quite alot of cool stuff in there so I've compiled a list and I'm gonna make an instructable using some of the parts, But I need ideas / help.Here are (the best) parts.2x sets of ultrasonic emitters / receivers2x LDRs large2x smaller photoresistors (used for line following)2x set of inrfa red emitter& reciever leds2x bright white leds + various others2x 9v motors & gear housingsLCD display 5cm squreeepromspeed controllers selector switches etcand a load of pre programmed processors that can't be reused.some more technical details here

Posted by madmanmoe64 10 years ago

### photoresistor

Hey!!i started working on a project based on ldr and i realised dc motor and ldrs don't work together so before i buy ac motors i wanted to ask that will it work??thanks in advance.

Posted by robo10302 5 years ago

### Changing the sensor

Hello guys, I want to make this circuit I just don't want any light to be visible. So, I was wondering if I could just change this LDR sensor to a IR sensor and still get the desired results.  Thanks,

Posted by HavocRC 6 years ago

### LDRS (Large Dangerous Rocket Ships) Rocket Competition hosted by Kari Byron

I just finished watching Kari Bryon hosting a Rocket competition on the Science Channel in Lucerne Valley California I Missed the initial showing on July 5th.   But they seem to be replaying it now and then (I saw it on July 10th, at 10 PM EST

Posted by Goodhart 8 years ago

### Would this require Programming?

Hi! I'm building a laptop bag alarm for a project I'm working on, and I'm pretty new to electronics. Would anyone know how I could make a system where a switch would be flipped to turn 'the alarm' on or off, and when that switch is flipped, the system would do nothing when the security system is triggered. The security system being 3-8 LDR sensors inside the bag, that will trigger some sort of logical part, that would be able to make the decision whether or not to sound the alarm, based on the status of the switch (flipped or normal)  I'm a programmer, so the system looks like this to me:  IF ALARM_SWITCH_ON && LDR_TRIGGERED { TRIGGER LIGHT && SOUND }  IF ALARM_SWITCH_OFF && LDR_TRIGGERED { DO NOTHING }  ELSE { DO NOTHING } Anyone know how this could be made with circuitry? or whether it would require programming? If it required all circuitry, is there anywhere I could get help with drawing up a circuit diagram?  Cheers & Thanks!  Karan

Posted by KodeKaran 7 years ago

### Solar 3w led fibre optic outside tree decoration

So I have salvaged a solar panel and the battery that it charged from a wireless alarm. The battery is 6v 1.2amps. My plan is to have the panel charge the cell during the day (its Ni-Mh) and using an LDR light a 3w led when its dark. The led will be connected to a number of strands of 1.5mm fibre optic cord, with a number of these attached to a tree to make it look.....nice. I have tested three strands of fibre optic cord with lengths of 2m with a lesser led and all appeared fine. I have a 3.7v 700ma driver (coming from China) which will drive one 3w led, along with heat sink. Now is where I am struggling a little, I am not massively experienced in electronics. I think I want a diode attached to the solar panel to avoid battery drain. Then a resistor to reduce my 6v to 3.7-4v and the LDR. Does this look like it would work in principle? Would the battery run 2 of these drivers/leds or would it discharge too rapidly? Thanks for any input!

Posted by earton 5 years ago

### (SOLVED) Break circuit = Make circuit?

Basically, what I want to do is activate something when there is no current somewhere else. Examples of uses of this would include turning an LED on when there is no light on an LDR and turning it off when there is light, rather than the other way around, along with turning an LED on when a circuit is broken by opening a door. Apologies if I have not been clear enough. Is this possible?  EDIT: Thanks to NachoMahma, I have it set up with a transistor. I will post a schematic if anyone is interested.

Posted by __DELETED__ 7 years ago

### Using a 3.5 tt screen to display speed from a laser chrono set up

Posted by PhilB68 2 years ago

### Throwies reimagined - Really I did tried :) :| :/

Seeing other forms of making interactive throwies, eg using microchips impresses me.However i think it is important that we try parts of the B.E.A.M philosophyhttp://en.wikipedia.org/wiki/BEAM_roboticsNamely keeping things simple, and avoiding the use of microprocessor.The component of a interactive throwie is that it has1. Power storage2. Trigger3. Circuit4. LED5. (optional) Power collection of radiant energy.I like to see more suggestion on ways we can address each issues.But to kick start the issue, can you see if my idea is feasible.essentially for my prototype not-yet throwie, I used a circuit from http://unconventional-airsoft.com/2003/11/16/momentary-fan-switch/#more-21to create a throwie that on sensing motion, doesn't flicker but turns on for a while.By ensuring that i use few and simple componants, i hope to keep cost per throwing down.Unfortunately my problem is that using a resistor to keep the capacitor from draining too fast from the base, actually decreases the voltage drop to an unacceptable level at the led.On my end it is unsolvable for the moment. Maybe you can work out how to make a cheap throwie, that can still do these functions or more.Any ideas how to solve this?Other Ideas for throwies1.Open and attach a switch to a barometer, to have a air presser passive trigger.2. A leave shaped pad with two conductors that do not touch, to act as rain sensors. (Resistance increase when leaf dries)3. Is sensitive to infrared radiation from side, so that the throwie is trigger-able by other activated throwies. (As well infrared devices)4. Has a short loop of coil to recharged capacitors, by outside induction.5. If activated rarely, uses a tiny single solar cell to charge capacitor.6. Has a hook to be easily collected for recycling. (Using a simple loop of wire on a pole [Like a dog catcher pole] )7. A single thermistors in series with led.8. A tricolour LED, and a Two light resistor. One LDR acts to sense if it is day an night, if night a low power light is activated. Only when an object strays near, and reflect light into another LDR, does the throwie get triggered at all.9. A throwie triggered by vibration.10. A throwie that responds to radio waves.

Posted by akimbo m 11 years ago

### Someone on LDR!!!

I'm new to this site, I'm interested in someone in a long distance. We both live 1900 miles apart I live in New Jersey and She lives in Central America. I first known her who's actually beknownst to my Step-Siblings of mine while she still is and was an employer at a Teen Clothing Store about two years ago which a Step-Sibling of mine owns the place. Just a month ago just hours before My parents and I we're to go back home as our Spring Break Came to a conclusion, We exchanged phone numbers so we can reach contact after I asked her's. Then weeks later I called her home and she's only answered once. I called once again many times the problem is that she doesn't still answer the reason for this is cause she barely uses her phone due to the High Violence there. I know the phone number to her job but the problem is that I don't want to get her in trouble since her boss isn't there all the time. Some think that She's rejecting me and she's not because she did gave me her number. If she wasn't interested in me She wouldn't give me her number. She doesn't even know how to use the internet or chat. Another thing is that She doesn't have a Home Phone Either. I plan on sending her maybe a letter but I want to see if u can tell me if I could also give her a Friend card or anything at all so she can cheer up. I plan to see her once again when we come back there this August and i'll tell her the truth if not I might go on. She only lives with her brother and Sister. She and Her sister work together there. Sometimes I feel confused that I really want to get to know her. Some think she has a boyfriend but she told me she's not cause they said that she does but I really can't buy what othes might say so It's good to feel with me to drop some comments. I'll just enjoy life as always doing what I do during my normal routines. I haven't thinked of her much then before I will keep that as a promise. We'll thanxs anyway!!!

Posted by Pcons16 10 years ago