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The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

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Old 12-11-2009, 07:19 PM
L_A_L_I L_A_L_I is offline
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Default why use timer 555


I'm interested with the project above which i found on the internet and I'm going to build it for my college assignment. One thing that i don't understand is why it used the 555 timer for the transmitter? What's the purpose of having the 555 timer in this circuit?
Will it still work without the 555 timer?
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Old 12-11-2009, 07:55 PM
Brother_of_the_wind Brother_of_the_wind is offline
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Its set up to run as an astable multivibrator - I think you need it if you want the lights to blink. What is this circuit trying to accomplish?
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Old 12-11-2009, 08:01 PM
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The project might be a challenge without component values.
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Old 12-11-2009, 08:03 PM
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It would have helped if you had included the link to the circuit description, like this:
http://www.redcircuits.com/Page40.htm

Circuit operation:
IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the car on the same line, a couple of centimeters apart, on a short breadboard strip fastened to the wall. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting inputs of three voltage comparators. These comparators switch on and off the LEDs, referring to voltages at their non-inverting inputs set by the voltage divider resistor chain R7-R10.

Now ask yourself, if you omit the IR transmitter portion of the circuit, where will the receiver get information?
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Old 12-11-2009, 10:43 PM
L_A_L_I L_A_L_I is offline
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Quote:
Originally Posted by SgtWookie View Post
It would have helped if you had included the link to the circuit description, like this:
http://www.redcircuits.com/Page40.htm

Circuit operation:
IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the car on the same line, a couple of centimeters apart, on a short breadboard strip fastened to the wall. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting inputs of three voltage comparators. These comparators switch on and off the LEDs, referring to voltages at their non-inverting inputs set by the voltage divider resistor chain R7-R10.

Now ask yourself, if you omit the IR transmitter portion of the circuit, where will the receiver get information?
Sorry bout the lack in my 1st post

At first I think the designer makes the proximity indicator LED to blink because the blinking transmitter, but with 120Hz frequency I think our eyes can't see the blink

@SgtWookie> Thanks for the addition

I mean will the circuit works if I connect the LED & resistor directly to the Voltage source and ground without connecting it to the 555 timer

Will it affect the output of the circuit?
If the circuit still works properly, then what's the 555 timer's function since its not a digital circuit...

Last edited by L_A_L_I; 12-11-2009 at 10:49 PM.
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Old 12-11-2009, 11:00 PM
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See C3? That effectively blocks the DC output of IC2A.

Otherwise, IC2A would just output a voltage corresponding to the ambient light level.

Since the IR emitter is flashing on and off, those transitions are coupled through C3, which blocks DC levels, yet passes the effects of AC; particularly sharp transitions.

So, it doesn't matter what the ambient light level is; as it's blocked.

If the IR emitter were on constantly, it would be blocked too.
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Old 12-11-2009, 11:10 PM
L_A_L_I L_A_L_I is offline
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I see
so that means the timer is very important
thanks for the answer Sarge
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Old 12-12-2009, 12:36 AM
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The circuit might indicate how close you are to a wall. It also indicates how clean or dirty is the wall because it shows the amount of IR that is reflected off the wall.

Hanging a tennis ball on a string and stopping when it touches your windshield is better.
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