That sounds like you did not use pullup resistors on the outputs of the LM393, as Eric suggested. Since the LM393 has open collector outputs, you are effectively letting the 151 inputs float to a logic high, which is poor practice. Use resistors in the range 4.7k to 10k (value not critical) from each 393 output to Vcc.

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Ron

 

Thanks a lot. I have added a 10K resistor from both O/Ps to the Vcc.

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Someone please help me out! I don't understand this problem: When the LDR isn't detecting any light inverting input gives around +3V (reference voltage) and the non-inverting i/p gives about +4.8V. but when i tune the POT(100K) this voltage doesn't fall below +4.6V. What could be the problem?? Both the comparators are giving such value.

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If you don't have any light on the LDR, its resistance will be much more than 100k, so the voltage on the noninverting input will not change much when you change the pot. Illuminate the LDR with the desired light level, then adjust the pot until the comparator output changes.

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hi Roff

Can you please suggest me what's the best combination of resistance and voltage for making the LEDs brighter? I have used six LED (transparent which emits red light) but the light is not bright enough. that's why my LFR is not working satisfactorily.

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hi ruzfactor,
Will you please post a simple sketch showing how and where the LED's are connected, also what type of LED.

I have looked back thru the posts and I cannot see a circuit for the LED's.

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"Good enough is Perfect"

PIC tutorials:
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Bill's: www.blueroomelectronics.com/

 

Here's a picture of how i placed the LEDs:

I have connected the LEDs with a common wire. The wire is connected to +6V with a 320ohm resistance (100 and 220 in series). Should I add more LEDs? I have run my LFR over a black surface with track made of white tape.

Attached Images

LED.jpg (232.7 KB, 6 views)

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Hi,
Are you saying you have connected 6 Red LED's in series like the drawing.???

Each LED has a forward voltage drop of 2Volts.

OR...

the second drawing. Which is it.?

Attached Images

	Image1.jpg (5.1 KB, 2 views)
	Image2.jpg (6.8 KB, 2 views)

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Eric
"Good enough is Perfect"

PIC tutorials:
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Bill's: www.blueroomelectronics.com/

 

hi,
Look at this drawing.

Three pairs of 2 LEDs [Red].

Attached Images

Image3.gif (3.8 KB, 6 views)

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Bill's: www.blueroomelectronics.com/

 

The LEDs are too dim because their current is too low.

Attached Images

Image2.PNG (11.3 KB, 3 views)

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hi ericgibbs

Not in series. They are connected in parallel as your second schematic.

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hi audioguru,

i'm now using two 9V batteries and using a 7812 for +12V from +18V in the circuit. This +12V is also used in 7806 for +6V supply. Previously I used an adapter for this purpose. How do I resolve this dimming of LED??

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Which voltage do you want to use for the LED's.?

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Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Little 9V batteries have a low output current and don';t last long.

When you power 2V LEDs from an 18V battery then 89% of the power from the battery is wasted.
You can connect 6 LEDs in series and in series with a 240 ohm resistor for a current in the LEDs of 25mA when the batteries are new and a very low current when the batteries are each 6V.

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The voltage which would make the LEDs brighter. Really these LEDs driving me crazy. My LFR is finished and because of LEDs, it's not working properly.

So what do I do now? I used two 9V batteries because it's cheap. A 12V rechargeable battery costs a lot!

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