All About Circuits

why use timer 555

L

Thread Starter

L_A_L_I

Joined Dec 11, 2009
3

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?
 
SgtWookie

SgtWookie

Joined Jul 17, 2007
22,230
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?
 
L

Thread Starter

L_A_L_I

Joined Dec 11, 2009
3
SgtWookie said:
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?
Click to expand...
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:
SgtWookie

SgtWookie

Joined Jul 17, 2007
22,230
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.
 
Audioguru

Audioguru

Joined Dec 20, 2007
11,248
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.
 
You must log in or register to reply here.
Thread starter Similar threads Forum Replies Date
micakoenig Timer-relay setup for reversing DC motor polarity General Electronics Chat 4
M Timer switch disco Analog & Mixed-Signal Design 5
U A circuit for a continuous running timer General Electronics Chat 5
R digital timer thc15a wiring General Electronics Chat 15
SyedAdilBukhari Trying to configure a 555 astable timer for a bike alarm but its not working!!!! Digital Design 11
Similar threads
Timer-relay setup for reversing DC motor polarity
Timer switch disco
A circuit for a continuous running timer
digital timer thc15a wiring
Trying to configure a 555 astable timer for a bike alarm but its not working!!!!

You May Also Like

Top