# get on/off information from switch connected to 16v, 500mA motor (record player)

Hi, I have a problem with my project and since my electronics skills are not the best and my Arduino experience is still kind of small I thought I'd ask around:

I have a record player that is started and stopped by a switch. I want my computer to know via serial from arduino if the device is turned on or off.

The power source is labeled with 16V, 500mA, Type: AC . My Voltmeter reads 21V AC at the switch (and directly at the power supply) when it's turned off, and 0 when the record player is turned on. Don't know why this is inverted, and why the measure is way higher than the 16V the power supply is labeled with.

Anyways: What I want to do is to have the Arduino check if the Record Player is switched on or off, but I am not sure how to do this properly.

I thought about connecting a second pair of cables to the switch and then putting the + into one of Arduino's Analog Inputs to have it read if there is voltage or not.

But: Do I have to lower the Voltage of 16V, and how? Can I just put a second pair of cables to the switch that controls the motor? How would I wire this properly?

Any help is greatly appreciated. Also if there is a different way to do this, please give me a hint. Thanks

Don't know why this is inverted,

Because the voltage across the switch is zero when the switch is on, the switch then is a short circuit.

Turn the AC into DC with a diode and capacitor, then reduce the voltage to 4V with a potential divider. Feed that voltage into the arduino input, and connect the grounds together.

One way to do it would be to use a voltagedivider and a diode (as it is AC)

A voltage divider: two resistors of ex: 4,7 Kohm and 33Kohm. If you measure over the small resistor through a diode it should give you a reading of about 3 V that kan be measure by your Arduino.

thanks for all the replys. first i will try to get me some dc current here to make it arduino compatible.
i foundt out why the reading is higher than the output is labelled. seems to be because it is an unstabilized power supply that draws higher currents when not in use.

because it is an unstabilized power supply that draws higher currents when not in use.

You need to get your thinking and terms straight. It does not draw any current when not in use, it has a higher voltage because there is no current drawn. When you start to draw current the voltage drops. The voltage printed on the supply will match the actual voltage out when the current printed on the supply is being drawn.