# Quad Tone Decoder Board



## pshort (May 6, 2008)

At the moment I've designed a 4-channel tone decoder board using four LM567 chips. It's a 1.45" x 2.5" PCB which has an audio input channel that drives four tone decoder chips. The idea here is that by using four adequately separated audio tones that four completely separate outputs can be created. These outputs could be used to independently drive four LED outputs (similar to what goneferal is describing), or four general digital outputs (such as those that halstaff is using for sending signals to a PICAXE), triggering motors, or used to send control signals to other devices, such as a PWM chip.

At the moment this is all experimental, just to see how things work out.


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## HomeyDaClown (Oct 3, 2009)

Sounds good. 

I remember years ago using similar 567 based designs to control things. I always ended up using multi-turn pots to be able to get an accurate tone decode. 

Now I prefer the newer chips that are crystal controlled, they decode much quicker (nice for prop triggering) and never drift off frequency.


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## pshort (May 6, 2008)

That's why it is experimental.

One thing that I will try to do, though, is to place the frequencies as far apart as possible and to make the passbands as wide as possible. Hopefully this will prevent or minimize the potential problem that you noted. Part of the testing, of course, is to deliberately install components that are at the ends of the tolerance bands, or even outside the bands.


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## fritz42_male (May 5, 2009)

I'm playing with a DTMF decoder board to do much the same. I bought the board in to save time but easy enough to build. Based on a crystal controlled HT9170 chip. Output is binary coded decimal so I just need to get that to straight outputs and then 10+ relays etc are no problem!


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## hedg12 (Jul 6, 2008)

My limited experiences with the LM567 were very much like Homeys, in that I never could get the things to hold frequency. But then again my analog design kung fu is not strong... 
I've often wondered if I would have had more luck if I would have filtered the audio signal ahead of the 567 with a simple bandpass filter to limit the range of frequencies it had to deal with. Just a thought.
I'll be watching this with great interest.


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## halstaff (Nov 18, 2009)

This sounds very interesting and I'll be watching this thread closely.


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## pshort (May 6, 2008)

Hmm...that DTMF solution seems a better choice. And since there are questions, I might just get some parts and test them further on a solderless breadboard. Especially since I have another project underway for my PCB prototyping dollars...


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## fritz42_male (May 5, 2009)

The board I'm using is from CS Technology and they give you a circuit diagram in the data sheet:

http://www.cstech.co.uk/dtmf_detector_details.pdf

I also have this diagram which shows how to drive the relays using a flip/flop so you send one tone to switch on and another to switch off. However, I want to send the BCD from the device into a decoder THEN the flip/flop so instead of driving 4 relays I can drive 10 or more.

http://www.electronic-circuits-diagrams.com/remotecontrolsimages/5.gif


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## pshort (May 6, 2008)

That, of course, assumes that the outputs of the DTMF chip don't glitch as the input tones transition.


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## fritz42_male (May 5, 2009)

The chip is designed to sort that out. If you want an extreme case then the chip provides a Data Valid signal which only goes high when certain conditions are met.

DTMF is tried and tested and been used for decades for such stuff.


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## corey872 (Jan 10, 2010)

If you're looking to go the DTMF route, there are some simple kits around which can handle the decode and output 16 channels:

http://www.hobbytron.com/R-TT-7.html

20mA output, so you could drive a LED or two directly, or use a relay for larger loads.


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