http://www.8051projects.net/ Learn to make simple microcontroller projects, pic, 8051, avr and arm projects. download 8051 projects, tutorials, libraries, sample codes. join the microcontroller discussion forum and ask doubts regarding electronics. the best source for 8051 over internet. en-gb 2009-01-08T12:07:17-08:00 contact@nospam.com hourly 1 2000-01-01T12:00+00:00 http://www.8051projects.net/forum-t9752.html 2009-01-08T12:07:17-08:00 i have some ldr and i want to make photo sensors with them !!! i tried to google but not found any circuit !!!i have small type ldr !!! please anybody, provide a circuit diagram with some details to use it with microcontroller(89s52) http://www.8051projects.net/forum-t9752.html 2009-01-08T12:07:17-08:00 Arun Kumar V Hi,i don't know your skill level with micros but you can try reading the LDR value with ADC and micro, display the value on lcd - simple light/lux meterArun http://www.8051projects.net/forum-t9752.html 2009-01-08T12:07:17-08:00 pdi33 note that an LDR responds in an extremely non-linear way to the light intensity. The resistance of a LDR aries from a few meg-ohms in dim light to a few kilo ohms in bright light (maybe even a few ohms depending upon the light intensity and LDR used.). So I would suggest that u first connect the LDR as shown below:VCC ------ LDR ------- 1K resistor -------- GND. and plot the voltage across the !K resistor w.r.t different light intensities on the LDR.then connect this voltage output to a ADC via a simple non-inverting op-amp ampilifier and connect the ADC to the uC as Arun suggested.U may require to make a lookup table in the coding part to convert the readings to a LUX value. http://www.8051projects.net/forum-t9752.html 2009-01-08T12:07:17-08:00 rahuljin thanks to both of u !!! i will try this http://www.8051projects.net/forum-t9752.html 2009-01-08T12:07:17-08:00 electronicfreak pdi33 wrote ...note that an LDR responds in an extremely non-linear way to the light intensity. The resistance of a LDR aries from a few meg-ohms in dim light to a few kilo ohms in bright light (maybe even a few ohms depending upon the light intensity and LDR used.). So I would suggest that u first connect the LDR as shown below:VCC ------ LDR ------- 1K resistor -------- GND. and plot the voltage across the !K resistor w.r.t different light intensities on the LDR.then connect this voltage output to a ADC via a simple non-inverting op-amp ampilifier and connect the ADC to the uC as Arun suggested.U may require to make a lookup table in the coding part to convert the readings to a LUX value. can i connect directly to micro other than connecting to GND ,like thisVCC ------ LDR ------- 1K resistor -------- uC(ADC) http://www.8051projects.net/forum-t9752.html 2009-01-08T12:07:17-08:00 Arun Kumar V hi, No,you cannot connect LDR that way, you would be measuring Current and not Voltage.you need to connect one end of 1K resi to Gnd and connect the junction of LDR and other end of 1K resi to ADC, this way the analog voltage is referenced to Gnd.Arun