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i have small type ldr !!! please anybody, provide a circuit diagram with some details to use it with microcontroller(89s52)]]> Mon, 26 May 2008 02:49:02 -0700 http://www.8051projects.net/forum-t9752.html Re: help with ldr http://www.8051projects.net/forum-t9752.html 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 meter


Arun]]> contact@nospam.com (Ajay Bhargav) Mon, 26 May 2008 12:08:23 -0700 http://www.8051projects.net/forum-t9752.html Re: help with ldr http://www.8051projects.net/forum-t9752.html
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.

]]> contact@nospam.com (Ajay Bhargav) Mon, 26 May 2008 14:07:43 -0700 http://www.8051projects.net/forum-t9752.html Re: help with ldr http://www.8051projects.net/forum-t9752.html contact@nospam.com (Ajay Bhargav) Mon, 26 May 2008 18:35:27 -0700 http://www.8051projects.net/forum-t9752.html Re: help with ldr http://www.8051projects.net/forum-t9752.html 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 this
VCC ------ LDR ------- 1K resistor -------- uC(ADC)
]]> contact@nospam.com (Ajay Bhargav) Tue, 05 Aug 2008 21:30:47 -0700 http://www.8051projects.net/forum-t9752.html Re: help with ldr http://www.8051projects.net/forum-t9752.html
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]]> contact@nospam.com (Ajay Bhargav) Wed, 06 Aug 2008 02:39:22 -0700 http://www.8051projects.net/forum-t9752.html