Hello,
I want to build a DTMF (Dual Tone Multiple Frequency) project and need some help. I'm using a MT8870 decoder IC that takes a signal from the phone and decodes it to a binary output. I seen one on youtube: - YouTube and went with it. Yet, the LEDs are always on??? At 1.715 volts. The decoder does decode the input phone signal and the LEDs get brighter in relation to the correct digit pressed. So first question is should I put a resistor before the led to have a voltage drop so the LEDs turn on dimly at ~.7 V??? Now, here comes the real question I need some support on. This decoder outputs four digital signals. I need to route these to my Arduino Uno R3. I'm wanting to put them directly into the digital inputs. But, the manual says they the Arduinos digital inputs are running at 5V. Will the decoder output be read by the Arduino??? And if so how would I program the Arduino to take these inputs from the decoder output and control a motor. For example if I pressed 1 the motor turned on. Then if I pressed 2 it ran faster and 3 faster, etc. And zero to turn off. I appreciate all your help on these questions ad any intuition you can provide me.
I can't help with the DTMF side of things but the Arduino side of things sounds relatively simple.
I suggest that you test it first using pushbuttons as inputs. That way yo don't have to worry whether the DTMF system is working.
Wire 4 pushbuttons to 4 Arduino input pins using a resistor between the pin and GND to hold it LOW and the pushbutton between the pin and 5V to take it HIGH when when the button is pressed. Note that there is a simpler way to wire them that does not need an external resistor but it may not be appropriate when used in conjunction with the DTMF unit, hence this suggestion, but see below. Now use the examples in the Arduino IDE Digital section to experiment with reading the inputs and reacting to them.
You will not be able to drive the motor directly from the Arduino as it cannot provide enough current so you will need a motor shield or at least some external electronics connected to an output pin in order to do it. Connect the motor however you decide to do it and try outputting a PWM signal to the pin controlling it and the speed should vary. The IDE Fade example will show you how to do this.
The next phase is to combine the 2 ideas. Read an input and when it changes from LOW to HIGH (IDE State Change example) change the output PWM value appropriately. Take it one step at a time an don't try to do everything at once. Use Serial.print() to show you the value of variables at various points in the program and to indicate which section of code is being executed. Once everything is working you can take them out.
Once you have the DTMF sorted out you can replace the pushbuttons with connections to the DTMF circuit to take the Arduino inputs HIGH. If the the DTMF unit takes them LOW then you can reverse the Arduino logic and wiring to accomodate this.