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What i know is .....
To measure watt, we usually have voltage * current.
The meter reading for the kWh of our household will be accumulated by time.
What about **broken link removed** tells you?
It only displays watt instantaneously?
If you want to build the wattmeter project, you can modify the code to find kwh. Read the wattage every second, add the watts up, divide by 3,600 to get watt-hours, divide again by 1,000 to get kwh.
If you want to build the wattmeter project, you can modify the code to find kwh. Read the wattage every second, add the watts up, divide by 3,600 to get watt-hours, divide again by 1,000 to get kwh.
Mainly the fact that it's AC. R15 is a "shunt resistor", and this is fine for DC circuits, but for AC it gets a little more tricky. You need to amplify the sine wave on it first, then rectify and filter it to measure it.
Also because it's connected to the mains, you are going to want to isolate it. You may want to consider using something like an HCPL-7510-000E optoisolator (designed for this kind of work) or better still use a current sensing transformer like a LEM "LTS 15-NP" or equivalent so you don't have to dick with a +5V supply on the hot side of the circuit for the opto.
AC seems a bit tricky for me.
Well ... as the project goes i just wonder, how it knows the value of current and the voltage input?
Which of the component is responsible for this? As i know port A is getting the analog input.
AC seems a bit tricky for me.
Well ... as the project goes i just wonder, how it knows the value of current and the voltage input?
Which of the component is responsible for this?
I just told you - it's R15, the shunt resistor. Current goes through it, develops a teeny tiny voltage, the opamp multiplies it, the processor reads it. Standard way of doing it with DC. With AC you really want an inductive transducer.
Don't make a shunt resistor - buy one. It's too difficult to predict and read the actual value, copper wire has too high of a temperature coefficient to be trusted.
Don't make a shunt resistor - buy one. It's too difficult to predict and read the actual value, copper wire has too high of a temperature coefficient to be trusted.
ya.... i juz manage to get myself a 1Ohm resistor. I know the schematic doesnt use this value.
but seems like shunt resistor cost a lot too if compare to my project... sigh**
ya.... i juz manage to get myself a 1Ohm resistor. I know the schematic doesnt use this value.
but seems like shunt resistor cost a lot too if compare to my project... sigh**
A 12 Inches piece of 10 AWG Copper Wire is Close to .001 Ohms.
Its Not quite as good as a Proper Shunt as it will have more drift with temperature, But MUCH Better than your 1 Ohm shunt for the Resistance. (AND MUCH CHEAPER.)
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