Microphone for TT7 tone detector kit

[demon4]

I am trying to connect a microphone to the TT7 kit's audio input. Is there a circuit diagram available for this? I would like to use either MC1 Miniature Electret Condenser Microphone from Ramsey for input or a simple condenser microphone from Radio Shack 270-092.

I would like to use the amplifier part from the circuit on the bottom this page: http://members.cox.net/rbirac3/Snuffy/tone_detect.htm using a simple 741 op amp circuit (1458 chip is two 741s) . However, the tone detector chip they use NE567 has a much lower input resistance of 20 K Ohms while the TT7's MC145436 chip has an input resistance of approximately 100 K Ohms. I am worried that the higher resistance will for the TT7's chip will require more amplification but don't want to damage the chip. I am also considering using a Audio amplifier such as this one LM386.


I can't anything on the manual. Thanks!

[RDEngineer]

The circuit you are refering to is a simple single tone detector. You need only the amplifier before it for your purpose. You need to have an input signal level between -29dBm and 1dBm for the HT9170 tone decoder in the TT7 to operate properly. Since a microphone typically has a very low level input and you are going to use an electrite microphone you need to have the amplifier and a bias setup for the mic for the circuit to operate. It appears that your circuit will provide everything you need. We don't provide design suport for custom applications but try it and see. Maybe someone on the forum will share there knowledge with you. You're on the right track.

Have fun and enjoy.

[demon4]

Not having any luck. Any tips? I can't get the microphone to work even on a set of speakers.

Thanks for the advise.

[RDEngineer]

The circuit you refered to should work fine. Make sure you include the coupleing capacitor that is connected to the 576 in your setup. If you are using an op amp you will probably not be able to drive a speaker. If you have a high impedance set of headphone,(many headphnoes today are 40 ohms or more) you may be able to hear a signal on the op amp output. Otherwise you will need an oscilloscope to "see" the signal. You don't need to be able to drive a speaker. As long as you have the proper levels and everything si working properly then it should work. Half the fun of a hobby is making it work and learning. Make sure you have everything wired correctly. Not knowing how you are sunig the "system" it is not possible to tell you what the problem is. Again we can not provide design/troubleshooting services for custom applications.

[demon4]

Thanks RDEngineer. Working now! Ramsey is a great company to provide excellent products and such quick support. The circuit was okay but I had to put the microphone up very close to the speakers for the decoder to detect the tone. I would like to be able to use this from 1-3 feet away from a cell phone speaker phone. Is this a pipe dream or could a better amplifier circuit do it? Thanks again and sorry if this is a custom application. Just want to know if it's worth my trouble to continue or if it is probably not possible. My speaker is pretty good, about 85 dB at 4 inches away. Right now I'm using one op amp from a LM324 chip and the amplifier portion of the circuit diagram I posted earlier. Is there a amplification kit I could buy from Ramsey possibly? Thanks again!

Here are some possible amplification circuits I am considering:

http://www.josepino.com/circuits/ind...fier_lm386.jpc
http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

http://www.techlib.com/electronics/audioamps.html
http://headwize.com/projects/showfil...=opamp_prj.htm figure 12b

http://www.tricountyi.net/~randerse/amp.htm

[RDEngineer]

There are too many variables involved to give you an answer. The key is to have enough clean signal level into the decoder. Sensitivity of the micc, gain of the amplifier, amount of ambient noise, attenuation of the sound level as you move away form the source and on and on and on, all come into the equation. The probablilty of being able to have it work reliablilty at that distance is probably very small under normal conditions. Just try and learn.