# Thread: 38 khz ckt problem

1. ## 38 khz ckt problem

i have fixed the ir emmitter ckt given in this site.it is emmitting some radiation but the tsop 1738 is not responding accordingly.tsop is responiding i.e. i can see some voltage drop when i check it ith a tv remote.but i cud nt see any change with this emmitter ckt.plz help me.

shank

2. The o/p pin must go LOW when the sensor detectsn 38Khz IR.
The TSOP will need a continuously chopped 38Khz signal to reliably go low and stay there. It will not respond for long to a continuous 38KHz signal.

3. I have fixed the ir emmitter ckt given in this site

4. ## CHOPPED???

if i have to give a chopped signal.den how can i do it for object detection???i have to interface it with microcontroller.will i have to give the power to the emitter ckt in intervals.how cud i do it in ckt???plz help.ill try with ur suggestion.thanxx
--shank

5. Have you made a 38KHz osc using 555 IC ???
Then ., make another one with 10 times the RC value. You will get an oscillator working at ~3.8KHz.

Use this o/p to trigger the pin 2 of the 38KHz Osc.

Alternately, feed the 3.8khz and the 38khz into a AND gate. The O/p of the AND will be a 38KHZ chopped 3800 times by the second 555 osc.
Put a .1 to 1ufd cap from AND o/p to ground.

6. ## is it necessary ?

Have you made a 38KHz osc using 555 IC ???
Then ., make another one with 10 times the RC value. You will get an oscillator working at ~3.8KHz.

Use this o/p to trigger the pin 2 of the 38KHz Osc.

Alternately, feed the 3.8khz and the 38khz into a AND gate. The O/p of the AND will be a 38KHZ chopped 3800 times by the second 555 osc.
Put a .1 to 1ufd cap from AND o/p to ground.
you have always mentioned to " pule of pulses" concept ... I tried your one ..I works great .. what I did was I generated a 38Khz with my uC and the uC's enable pin was fed with another one uC(just tp test... ) what I found that it responds great ... upto a clearance of 3m !! ... but when I used 555 I did not need and thing as u mentioned above ... but still got a clearance of 27 cm ... can u plz tell me ..what it diff of generating 38Khz from uC and from that of 555,

Does 555 generate pulses of pulses... and uC doesnot ?

7. TSOP 1738 doesn't respond to continuos 38 KHz. To be triggered it requires pulses of 38 KHz.
Look at the datasheet for more information, it is given in detail.

8. you have always mentioned to " pule of pulses" concept ... I tried your one ..I works great .. what I did was I generated a 38Khz with my uC and the uC's enable pin was fed with another one uC(just tp test... ) what I found that it responds great ... upto a clearance of 3m !! ... but when I used 555 I did not need and thing as u mentioned above ... but still got a clearance of 27 cm ... can u plz tell me ..what it diff of generating 38Khz from uC and from that of 555,

Does 555 generate pulses of pulses... and uC doesnot ?
Confusing !! you generated a train of pulses from 2 uc, and then ask, if uc generate pulses??

its not just the pulses, its the CURRENT. 555 normally source more current than a uc. The more current, the better the IR intensity.
the max rating for pulsed current is always greater than the max rating for cont. current. So, be it a uc or a 555, as long as the shape of the pulses are fine, and you drive the LED with a good driver (say, a simple transistor), things will be just fine.

9. A uController generates clean pulses that are accurate and stable compared to a 555 oscillator. Besides, the 555 Osc RC components may not be stable because of bad /cheap capacitor. The pulses may not have sufficient amplitude, constant pulse width, undistorted wave form, symmetrical duty cycle......
The TSOP looks for clean pulse trains, compares noise versus Frequency and adjusts its gain according to the above mentioned conditions. his will lead to a simulated 'attenuation' of the modulated IR emission.
Since you have some expertise in uC programming, it will be better to derive the Modulated 38Khz signal from a uC itself.

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