1watt step down 240ac > 16vac Transformer + Arduino

OK, I decided to not take any risks, my Transformer (dinky little thing) arrived today.

Thing is, I want to monitor that 16v ac feed, before I place a resistor divider and feed it into analog in port, how's the negative voltage side go? my aim is to read in the waveform to see how clean it is, for simplicity sakes i'll run it through a diode and only pass + waveform, that way i can have 0-5v via the divider.

my concern... should i use a Zener 5v1 diode to clip the voltage? (Obviously, my goal is to check the condition of the power, under voltage, over voltage... maybe place my voltage divider to give 4v (max) and >4.1v flag as over voltage?. that way I could definitely use a zener to clip the voltage 5v since it should never reach 5v (unless there's a power spike)....

As long as the transformer cleanly replicates the sinewave and it's signal....

I've often wondered how clean electricity when storms are around, i'm curious to see if lightning strikes and other disturbances could be filtered out and detected, even if it's just to flash an LED to indicate fluctuations for now.

You can find a lot here: http://openenergymonitor.org/emon/

A transformer can be used to monitor the primairy voltage, but only if it is not used to power something else and if the the iron core of the transformer is not in saturation. So you can’t use that transformer to power the Arduino.
If the transformer gets warm without any load, the iron core is in saturation and you better use another one.
Or you could use two identical transformers in series.

You have to bring the AC voltage into the 2.5V range. You can use a resistor divider for that. You could even pass the voltage of the resistor divider to an analog channel of the Arduino.
I think the AC signal should be between 1…4V. If you are expecting high peaks, perhaps 2…3V.
A larger voltage is no problem if the current is not above 1mA, but you better use clamping diodes to ground and 5V and an extra 1k resistor to the input of the Arduino.

What kind of disturbances do you want to measure ? What should the sample rate be ?
Turning on a washing machine or electric kettle should cause a disturbance, you can use that to test the sketch.

Ah ahhh!

Nope, i'd be using the transformer for nothing except to feed it into the analog 0 port, and get a value, 1k resistor and a voltage divider to drop it to 3.5v...

And yes, I'm curious to see how switching on appliances effects the wave form, heavy traffic going by (spark plug disturbance) hell yes...

as for sample rate, I'm sure Arduino can handle a 50hz signal right? lol Sample rate, a low one but one high enough of a resolution to detect voltage spikes ...

But what do you think should be done with the negative half of the cycle? would the analog value go into the minus range? eg 1024 = max . 0 = min does -1024 exist? never looked, the Arduino will be powered from a seperate source, i'll get the shrink tubing out and power this transformer and check for any heat.


I was going to post it's "specifications" but when it says "Material " Metal, Magnet, Electric Parts" it's not exactly very useful information.

I'm using an Uno, I could get a higher sample speed from the Due, but i'd have to use something like 0-1.5v :O nah uno sounds a lot better....

Spikes is the problem. How short are the spikes you want to detect ? Perhaps 1000 samples per second ? That should be possible.

You should read/study the openenergy site.

Not just 1k to arduino input !

Take a look at this. http://openenergymonitor.org/emon/buildingblocks/measuring-voltage-with-an-acac-power-adapter

The signal is set into the 2.5V range with a resistor divider (they use 2 * 470k plus capacitor). The signal is lowered with voltage divider (they use 100k and 10k). After that, the signal from the 100k/10k can be clampled with diodes to GND and 5V and extra 1k to the Arduino input. But everything else is still needed.

The adapter does influence the waveform a little. http://openenergymonitor.org/emon/buildingblocks/different-acac-power-adapters