Forums

Tone decoder debug

Started by Ralph Olsen December 31, 2011
I have been trying to get this circuit to work all morning. The LED's
are supposed to turn on when a 19.2KHz tone appears on the LM567's
input.

Here is the circuit. Originally downloaded off the net (identical from
2 sources) but I re-drew it in DipTrace to send here for clarity.
Click the image to enlarge.

http://www.4shared.com/photo/c5MHZYBD/Tone-decoder.html

Any suggestions where the problem might be?  ... apart from me that
is.

Ralph


On Dec 31, 8:09=A0pm, ralphol...@montrose.com (Ralph Olsen) wrote:
> I have been trying to get this circuit to work all morning. The LED's > are supposed to turn on when a 19.2KHz tone appears on the LM567's > input. > > Here is the circuit. Originally downloaded off the net (identical from > 2 sources) but I re-drew it in DipTrace to send here for clarity. > Click the image to enlarge. > > http://www.4shared.com/photo/c5MHZYBD/Tone-decoder.html > > Any suggestions where the problem might be? =A0... apart from me that > is. > > Ralph
Just glancing-- o Two of the wrong LEDs in series won't light from +5v. Try shorting pin 8 to GND -- the LEDs should light. o 470 ohms looks like a hefty heavy load for pin 5. The datasheet doesn't spec drive capability, but 4.7k and 10nF would be safer. -- Cheers, James Arthur
On Sat, 31 Dec 2011 17:59:25 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

>On Dec 31, 8:09�pm, ralphol...@montrose.com (Ralph Olsen) wrote: >> I have been trying to get this circuit to work all morning. The LED's >> are supposed to turn on when a 19.2KHz tone appears on the LM567's >> input. >> >> Here is the circuit. Originally downloaded off the net (identical from >> 2 sources) but I re-drew it in DipTrace to send here for clarity. >> Click the image to enlarge. >> >> http://www.4shared.com/photo/c5MHZYBD/Tone-decoder.html >> >> Any suggestions where the problem might be? �... apart from me that >> is. >> >> Ralph > >Just glancing-- > o Two of the wrong LEDs in series won't light from +5v. Try >shorting pin 8 to GND -- the LEDs should light. > > o 470 ohms looks like a hefty heavy load for pin 5. The datasheet >doesn't spec drive capability, but 4.7k and 10nF would be safer.
Yep. I dug up a TI data sheet (watermarked OBSOLETE on every page; not comforting ;-) that shows "R1 6.8 to 15K" as "typical" values. I could be wrong but 6.8 ohms is a bit of a reach for a low end value so I'd go with their intent being 6.8K to 15K typical and use a good ol' 10K for a starter. I dug one of these out of the drawer (surprised I could find it, much less that I had one) and breadboarded up a quick test. With R1C1 at 10K and 4.4 nF (two 2.2 in parallel) the datasheet formula worked out to 20.7 KHz, with the actual response at 16 KHz. So, it kind of works. -- Rich Webb Norfolk, VA
Ralph Olsen wrote:
> > I have been trying to get this circuit to work all morning. The LED's > are supposed to turn on when a 19.2KHz tone appears on the LM567's > input. > > Here is the circuit. Originally downloaded off the net (identical from > 2 sources) but I re-drew it in DipTrace to send here for clarity. > Click the image to enlarge. > > http://www.4shared.com/photo/c5MHZYBD/Tone-decoder.html > > Any suggestions where the problem might be? ... apart from me that > is. > > Ralph
Is that 19.2 KHz signal a fairly clean sine wave? If not, it won't work. BTDT with a 1024 Hz pilot signal to monitor tower lights on one TV broadcast site at another that was 40+ miles away to meet FAA tower light requirements. I had a crystal controlled square wave and had to filter it to get the distortion to an acceptable level. -- You can't have a sense of humor, if you have no sense.
Thanks for the advice everyone. I changed C1 to a 472 and put a 50K
pot in series with R1 as a "sensitivity" control. All is good. now.

Happy New Year, 

Ralph
On Sun, 01 Jan 2012 22:23:47 GMT, ralpholsen@montrose.com (Ralph
Olsen) wrote:

>Thanks for the advice everyone. I changed C1 to a 472 and put a 50K >pot in series with R1 as a "sensitivity" control. All is good. now. >
Sorry, I meant C4.
On Jan 1, 5:23=A0pm, ralphol...@montrose.com (Ralph Olsen) wrote:
> Thanks for the advice everyone. I changed C1 to a 472 and put a 50K > pot in series with R1 as a "sensitivity" control. All is good. now. > > Happy New Year, > > Ralph
Happy New Year indeed! Thanks to Rich too, for breadboarding it. -- Cheers, James Arthur