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Electronics => Electronics => Topic started by: aruna1 on April 21, 2011, 09:32:24 AM

Title: LM567 help need
Post by: aruna1 on April 21, 2011, 09:32:24 AM

Hi
I'm working on a tone decoder for my ultrasonic receiver. my goal is to detect input signal and verify whether its 40kHz. I'm using LM567chip for this. circuit is tuned for 40kHz and measured at pin 5.

my problem is circuit isn't working as it should be (according to data sheet)


EDIT: please note in following diagrams C4 should be 0.02uF. I have incorrectly marked it as 0.001uF.


First attempt
This is the first circuit I tried

(http://i51.tinypic.com/24fepo4.jpg)

In this circuit LED does not light for the 40khz input signal. actually LED wont turn on what ever input it get.

Second attempt

Then my second attempt is disconnecting capacitor C1 from pin 1. then LED turned on dimly when there is no input and LED lights brightly when detecting 40kHz signal. this is the circuit

(http://i52.tinypic.com/11kjtll.jpg)


Third attempt

in my third attempt I connected 100k resistor from 5V to pin 1. after that LED is turned off when there is no 40khz input and LED turns on when detecting 40khz signal. but problem is now circuit responds to sounds other than 40khz signal.sounds like clapping and tapping sounds. when clapping LED blinks faintly.
here is the circuit
(http://i55.tinypic.com/bfhwdx.jpg)

Forth attempt

here I connected both C1 and R3 as in data sheet but result is same as attempt 1. LED doesn't turn on with or without signal
this is the circuit
(http://i56.tinypic.com/ab7tg.jpg)


This is kind a funny. I cant figure out what the heck is wrong. first I thought LM567 was burned so I brought another but results are same.

can someone help me here? I'm pretty frustrated. ??? :P
thank you

Title: Re: LM567 help need
Post by: MikeK on April 21, 2011, 02:40:24 PM

You might need to run your numbers again.  I used this calculator: http://www.vk2zay.net/calculators/lm567.php (http://www.vk2zay.net/calculators/lm567.php) with your values and got 181kHz with the pot at middle (5Kohm).

Title: Re: LM567 help need
Post by: aruna1 on April 21, 2011, 07:30:58 PM

oops sorry C4 is 0.02uF. I marked it in the above diagrams incorrectly. in actual circuit I have used 0.02uF as timing capacitor and it gives 40kHz when timing resistor is about 1.136k ohms.

as i said before I measured frequency at pin 5 and it is 40kHz.

Title: Re: LM567 help need
Post by: billhowl on April 21, 2011, 08:20:39 PM

I think your C1 & C2 is too large, try C1 0.02uF, C2 0.01uF

Title: Re: LM567 help need
Post by: aruna1 on April 21, 2011, 08:53:46 PM

Quote from: billhowl on April 21, 2011, 08:20:39 PM

I think your C1 & C2 is too large, try C1 0.02uF, C2 0.01uF

nope that didnt work LED wont turn on with input of 40kHz