LDR detector
in [Design]
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From: abajan on 19 Jun 2006 01:27 Hi I want explain my project in brief . please help me about make it . I want to have a LDR detector with variable range of light . let me explain more I connect a LDR to a LM2903 comparator and I want detect output in any condition ( in brightness and darkness ) but it not possible . I am amateur in electronic and I don't know what is wrong Please offer me a circuit for solve it . Thanks
From: Adelec Bakkal on 19 Jun 2006 02:30 You did not state the purpose of the circuit. Anyway you can try this: Combine the LDR in series with a fixed-value resistor to make a simple voltage divider which can act like a voltage source that varies with light. This makes the first part of it. Let's call the voltage at the LDR V_Light. Now you have converted the resistance of the LDR into voltage which can be compared to a reference. Now use a potentiometer to create a programmable voltage reference. You will use this to set the level that will trigger the comparator.Let's call this reference voltage V_Ref. The point is to have the comparator compare two voltages. And now you have them, V_Light and V_Ref. All you have to do now is to connect V_Ref to the 'reference pin' on the comparator, you can connect it to the 'inverting input', next is to connect V_Light to the 'V_in', or just the 'non-inverting input'. Going this way, the comparator will output a logic 1 if V_light is greater than V_ref, and a logic 0 if V_light < V_ref, and the other way around if you interchange V_Light and V_Ref (choose according to application). The behavior of the circuit depends on the trigger level you have set with the potentiometer, and the value of the resistor you have put in series with the LDR to form a voltage divider. You set the potentiometer according to the transition level between 'dark' and 'bright', this goes with trial-and-errors untill you get the satisfactory behavior. The comparator needs a pull-up resistor. Connect the output of the comparator to the positive supply through a 3K resistor. Any close value should do. Good Luck!
From: abajan on 21 Jun 2006 02:49 Adelec Bakkal نوشته است: > You did not state the purpose of the circuit. Anyway you can try this: > > Combine the LDR in series with a fixed-value resistor to make a simple > voltage divider which can act like a voltage source that varies with > light. This makes the first part of it. Let's call the voltage at the > LDR V_Light. Now you have converted the resistance of the LDR into > voltage which can be compared to a reference. > > Now use a potentiometer to create a programmable voltage reference. You > will use this to set the level that will trigger the comparator.Let's > call this reference voltage V_Ref. > > The point is to have the comparator compare two voltages. And now you > have them, V_Light and V_Ref. All you have to do now is to connect > V_Ref to the 'reference pin' on the comparator, you can connect it to > the 'inverting input', next is to connect V_Light to the 'V_in', or > just the 'non-inverting input'. > Going this way, the comparator will output a logic 1 if V_light is > greater than V_ref, and a logic 0 if V_light < V_ref, and the other way > around if you interchange V_Light and V_Ref (choose according to > application). The behavior of the circuit depends on the trigger level > you have set with the potentiometer, and the value of the resistor you > have put in series with the LDR to form a voltage divider. You set the > potentiometer according to the transition level between 'dark' and > 'bright', this goes with trial-and-errors untill you get the > satisfactory behavior. > > The comparator needs a pull-up resistor. Connect the output of the > comparator to the positive supply through a 3K resistor. Any close > value should do. > > Good Luck! Dear friend ; Thank you very much for your answer ; I used your idea and got good result Now I want advanced this circuit as I explain Imagine we want this circuit work in darkness and brightness automatically ! I mean when we change to sun light for example it can auto calibrate ref voltage . I explain more : In my project I use a laser beam that incidence to LDR and then I want detect it in op-amp output but it must work in room environment with normal light and sun light automatically without any adjust of potentiometer . in fact it must determine thresholds of voltage in both environment ..is it possible or no ? I think I need a auto adjust voltage changer that can make threshold voltage May you help me ? Thank you and I'm sorry for my poor English A.jafry
From: Ken Moffett on 21 Jun 2006 20:20 "abajan" <abdolahj(a)gmail.com> wrote in news:1150872573.829638.176200 @y41g2000cwy.googlegroups.com: > > Adelec Bakkal ????? ???: >> You did not state the purpose of the circuit. Anyway you can try this: >> >> Combine the LDR in series with a fixed-value resistor to make a simple >> voltage divider which can act like a voltage source that varies with >> light. This makes the first part of it. Let's call the voltage at the >> LDR V_Light. Now you have converted the resistance of the LDR into >> voltage which can be compared to a reference. >> >> Now use a potentiometer to create a programmable voltage reference. You >> will use this to set the level that will trigger the comparator.Let's >> call this reference voltage V_Ref. >> >> The point is to have the comparator compare two voltages. And now you >> have them, V_Light and V_Ref. All you have to do now is to connect >> V_Ref to the 'reference pin' on the comparator, you can connect it to >> the 'inverting input', next is to connect V_Light to the 'V_in', or >> just the 'non-inverting input'. > > > >> Going this way, the comparator will output a logic 1 if V_light is >> greater than V_ref, and a logic 0 if V_light < V_ref, and the other way >> around if you interchange V_Light and V_Ref (choose according to >> application). The behavior of the circuit depends on the trigger level >> you have set with the potentiometer, and the value of the resistor you >> have put in series with the LDR to form a voltage divider. You set the >> potentiometer according to the transition level between 'dark' and >> 'bright', this goes with trial-and-errors untill you get the >> satisfactory behavior. >> >> The comparator needs a pull-up resistor. Connect the output of the >> comparator to the positive supply through a 3K resistor. Any close >> value should do. >> >> Good Luck! > > > Dear friend ; > > Thank you very much for your answer ; > I used your idea and got good result > Now I want advanced this circuit as I explain > Imagine we want this circuit work in darkness and brightness > automatically ! > I mean when we change to sun light for example it can auto calibrate > ref voltage . > I explain more : > In my project I use a laser beam that incidence to LDR and then I > want detect it in op-amp output but > it must work in room environment with normal light and sun light > automatically without any adjust of potentiometer . > in fact it must determine thresholds of voltage in both environment > .is it possible or no ? > I think I need a auto adjust voltage changer that can make threshold > voltage > May you help me ? > Thank you and I'm sorry for my poor English > A.jafry > > A. Jafry, I think I understand what you are trying to do. You are trying to distinguish when a laser beam touches your LDR in either sun or low light conditions. You are looking for the "change" form a background light condition. Is this correct? Ken
From: Jim Thompson on 21 Jun 2006 20:24
On Thu, 22 Jun 2006 00:20:33 GMT, Ken Moffett <KMoffet(a)mn.rr.com> wrote: >"abajan" <abdolahj(a)gmail.com> wrote in news:1150872573.829638.176200 >@y41g2000cwy.googlegroups.com: > >> >> Adelec Bakkal ????? ???: >>> You did not state the purpose of the circuit. Anyway you can try >this: >>> >>> Combine the LDR in series with a fixed-value resistor to make a >simple >>> voltage divider which can act like a voltage source that varies with >>> light. This makes the first part of it. Let's call the voltage at the >>> LDR V_Light. Now you have converted the resistance of the LDR into >>> voltage which can be compared to a reference. >>> >>> Now use a potentiometer to create a programmable voltage reference. >You >>> will use this to set the level that will trigger the comparator.Let's >>> call this reference voltage V_Ref. >>> >>> The point is to have the comparator compare two voltages. And now you >>> have them, V_Light and V_Ref. All you have to do now is to connect >>> V_Ref to the 'reference pin' on the comparator, you can connect it to >>> the 'inverting input', next is to connect V_Light to the 'V_in', or >>> just the 'non-inverting input'. >> >> >> >>> Going this way, the comparator will output a logic 1 if V_light is >>> greater than V_ref, and a logic 0 if V_light < V_ref, and the other >way >>> around if you interchange V_Light and V_Ref (choose according to >>> application). The behavior of the circuit depends on the trigger >level >>> you have set with the potentiometer, and the value of the resistor >you >>> have put in series with the LDR to form a voltage divider. You set >the >>> potentiometer according to the transition level between 'dark' and >>> 'bright', this goes with trial-and-errors untill you get the >>> satisfactory behavior. >>> >>> The comparator needs a pull-up resistor. Connect the output of the >>> comparator to the positive supply through a 3K resistor. Any close >>> value should do. >>> >>> Good Luck! >> >> >> Dear friend ; >> >> Thank you very much for your answer ; >> I used your idea and got good result >> Now I want advanced this circuit as I explain >> Imagine we want this circuit work in darkness and brightness >> automatically ! >> I mean when we change to sun light for example it can auto calibrate >> ref voltage . >> I explain more : >> In my project I use a laser beam that incidence to LDR and then I >> want detect it in op-amp output but >> it must work in room environment with normal light and sun light >> automatically without any adjust of potentiometer . >> in fact it must determine thresholds of voltage in both environment >> .is it possible or no ? >> I think I need a auto adjust voltage changer that can make threshold >> voltage >> May you help me ? >> Thank you and I'm sorry for my poor English >> A.jafry >> >> > >A. Jafry, > >I think I understand what you are trying to do. You are trying to >distinguish when a laser beam touches your LDR in either sun or low >light conditions. You are looking for the "change" form a background >light condition. Is this correct? > >Ken Modulate the laser, then AC-couple (and/or DC-restore) the receiver. ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |