Alarm Clock Integration via Speaker Voltage - Newb

Hello all. I’m a novice to this when it comes to microprocessors. I’m looking to start my first project but have a very basic question that I can’t seem to find any information on, mostlikely due to my ignorance to the terminology. Project entails taking a previous alarm clock and using the buzzer as an input to do other actions with the arduino. I know this is very basic but is this easily achieved as it will be just reading for voltage… After seeing all the tutorials on adding pots and light sensors I’m realizing these are resistors that work by putting current through them and measuring difference in resistance. What happens if there is already current through them and using it as a switch more or less. Again, pardon my ignorance. It seems like I would either need to use a transistor or a relay of some sort for this correct? Let me know if I’m way off or if I’m heading in the right direction. Thanks again guys. :grin:

I know this is very basic but is this easily achieved as it will be just reading for voltage... After seeing all the tutorials on adding pots and light sensors I'm realizing these are resistors that work by putting current through them and measuring difference in resistance.

Usually, you are looking for a change in voltage caused by a change in resistance.

For example, with two resistors in series, the voltage gets divided aross the resistors proportionally to the resistance ratio. If apply 5V across two equal-value resistors in series, each resistor will have 2.5V across it. If you increase the resistance of one resistor, the voltage across that resistor goes up.

It would be helpful for you to study some basic electronics (Ohms Law, series & parallel circuits and how voltages divide & current flows in series & parallel circuits, etc.) If you were studying electronics in school, you'd take at least a year of electronics before learning about microcontrollers. ;) I'm not saying you need to study for a year before you start having fun... I'm just saying there's a LOT to learn...

What happens if there is already current through them and using it as a switch more or less.

If a photoresistor is being used in a circuit, you should be able to hook-up an Arduino input to detect the change in voltage without affecting the existing circuit.

The biggest danger is connecting the Arduino to an unknown voltage that's too high (or negative), damaging the Arduino.

Maybe I'm not explaining this correctly. Basically I want to digital read a wire from an external source to see if it has voltage or not. Almost using the voltage to switch/notify the arduino to do other commands. Weather this input voltage is 9 volts or 5 volts I can change it with a resistor. I'll give an example of how I would think the circuit would go. A standard alarm clock will be plugged into the wall (Alarm clocks Power Source). At a desired time the alarm will sound the buzzer as it was designed to. Say I want to eliminate the buzzer and make the positive wire from the alarm clock a input to the arduino so the arduino can output to a LED lets say. Do I have to use a relay or transistor to do this or can I just resistor the line in from the buzzer and read from that? My confusion resides in connecting the two circuits. Is it an issue to do this as they both don't have a common ground? Thanks.

So, I just did it, works fine on analog pins. The Buzzer/Speaker from the alarm is running at 6.5 volts when buzzing. On the negative wire of the buzzer I did a 200ohm voltage divider with my output to an analog in pin (brining it down to 3.25 volts. Made some basic serial read code and it works fine. Don't know exactly what this did on the alarm side because the buzzer still work but not worried about that. Thanks