DTMF circuit with LM8705

SgtWookie

Joined Jul 17, 2007
22,210
We won't be able to help you unless you give us a lot more information.

Like, the schematic to your circuit, what it is and is not doing, and if there is anything different between your circuit and the schematic.

It would help a lot if you could also post a photograph of how you built your circuit.
 

praondevou

Joined Jul 9, 2011
2,942
1st question:

Are you supplying 22VAC to the LM7805? I don't hope so. The AC needs to be rectified, smoothed and then you pass the obtained DC to the 7805. Should be similar to this:


It would be interesting to know if 22VAC is really the maximum you can get out of the transformer. Under no load condition the DC would be very near to the maximum input voltage of the 7805. You also waste a good amount of power in the regulator.

2nd question: How did you hook up your mobile headset to your circuit?
 

praondevou

Joined Jul 9, 2011
2,942
What do you measure at Vdd and VRef , pin 18 and pin 4 of the DTMF decoder?

Can you post a picture of what you have built?

What exactly does the circuit do? Nothing? Or not what you expected?

Do you have an oscilloscope to measure the input voltage level?
 

JingleJoe

Joined Jul 23, 2011
186
Oh no, this is "one of those threads".
Maybe the poster has some sort of linguistic impairment, but I get the feeling they may be beyond help. ... Or beyond my ability to understand them in order to help.
I give you chaps credit for trying. Carry on the good work :)
 

praondevou

Joined Jul 9, 2011
2,942
this is my circuits is it correct th +5V and -5V same i connected to the circuits or I have to but Ground to the circuits ?
It looks correct, except for the fact that -5V shouldn't be called "-5V" but "Gnd" or "zero".

Check if you have 5V from pin 18 to pin 9.

If you have an oscilloscope, check the signal at GS and OSC2, pin 3 and 8 and post the results here.

What is pin 6 connected to? It should be left open or tied to Gnd.
 

SgtWookie

Joined Jul 17, 2007
22,210
The outputs have VERY low current source/sink capability. You really need to use transistors or MOSFETs in order to drive your LEDs. The LEDs will be quite dim unless you use driver transistors.

We do not know where you are, so we don't know what kind of parts you can get. You should put your Country and state or province in your profile. Click on the "User CP" link below the thread title, then click on the "Edit Your Details" link on the left, and then fill the information in under "Location" - then click the "Save changes" button near the bottom.

For the transistor driver, you will need ~2K resistors from the IC outputs A-D to the bases of general purpose NPN transistors.
The emitters of the transistors get connected to ground.
The collectors of the transistors get connected to the cathodes of the LEDs
The anodes of the LEDs are connected to the 220 Ohm resistors
The other side of the resistors is connected to +5v.
 
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SgtWookie

Joined Jul 17, 2007
22,210
In your circuit, "ground" is the 0v reference point. You have to declare some point in your circuit to be 0v/GND, or else it becomes difficult to report measurements.

If you changed all of your "-5V" notations to "GND", or simply omitted (remove) them where there is a GND symbol, then you would be less confused.
 
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