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Trouble with LM567

George O'Brien

May 26, 2014
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May 26, 2014
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Hello,

I am trying to get an LM567 to respond to an output from a 555 timer in the astable mode. The R1 and C1 for the LM567 are 10KHz and 6.1uF. The other components are the same as on the data sheet in the drawing with the multiple tome decoders (I'm just using one of these tone decoder circuits). I may have damages the LM567 because the voltage I measured on the input was about 8VRMS which would give a peak voltage higher than the max tolerable on that pin. I lowered the voltage with a voltage divider but there was still 6 VRMS on the input although the divider output was 1VRMS. I don't know why. I don't have a scope. The LM567 output doesn't go low for any frequency in the range the 555 was set for. I will try to provide a schematic, but I need a little more time. I don't have a working scanner or cad software.

George
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Paintbrush works. Also there are several tools available on line
 

George O'Brien

May 26, 2014
5
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May 26, 2014
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Here it is. Sorry It is upside down. Perhaps I will have to return to the library to rescan it.
 

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duke37

Jan 9, 2011
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And here it is if you are in Australia!
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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With the components you have chosen, I calculate the capture frequency is about 14kHz.

The frequency is approximately 1 / (1.1 * R1 * C1)

See here.

Perhaps this is your problem? (possibly not, since the 555 should oscillate at between 13kHz and 16kHz based on your stated components.

My concerns with the 555 oscillator is that you are using a very low value capacitance. Any leakage could easily change the frequency significantly (as could stray capacitance). I recommend you increase your capacitor by a factor of 10, and reduce the resistors by a factor of 10.

I note that your C2 is larger than the value shown in a circuit in the datasheet. I'm not sure if this will have any effect.
 
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