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Step 3Construct the AC-to-DC Conditioner Circuit
The main drawback with using an AC clamp is that the mV output is also AC. This isn't a problem for a multi-meter since it can be set for measuring AC voltages. However, the ioBridge module is expecting a DC voltage on its analog input pin. Therefore a little signal conditioning is required to convert the AC RMS value into a DC equivalent. The circuit I used was my own design and used components I had on hand, so I'm almost certain that it's less than ideal. After I was done soldering it up, I found a simpler circuit here. You may want to try it instead.
The main component in the circuit is an Analog Devices AD8220 instrumentation op-amp. This part only comes in surface mount style packaging. I needed to use a tiny SMT-to-DIP adapter board for my circuit. Don't feel like you need to use the exact same part. Any rail-to-rail instrumentation op-amp will work just fine. For example, the AD627 (Analog Devices) will work too and it comes in a breadboard friendly DIP package. In my circuit, I used a 16k resistor to achieve a gain of 4. Feel free to use a different resistor to get to a particular gain you need. However, any change in gain must be compensated for in the JavaScript of the webpage.
The other part of the circuit is a leaky peak detector made with a diode, resistor and capacitor. Its purpose is to translate the AC wave peaks into a DC voltage level. The 47k resistor causes the leakiness. Since the voltage level updates 60 times per second, adding that resistor increases the system's response time.
The potentiometer is used for offset calibration. I used a 15-turn pot for the best accuracy. To calibrate, power the circuit, make sure the AC clamp is not on any wire and measure the circuit's voltage output.
The main component in the circuit is an Analog Devices AD8220 instrumentation op-amp. This part only comes in surface mount style packaging. I needed to use a tiny SMT-to-DIP adapter board for my circuit. Don't feel like you need to use the exact same part. Any rail-to-rail instrumentation op-amp will work just fine. For example, the AD627 (Analog Devices) will work too and it comes in a breadboard friendly DIP package. In my circuit, I used a 16k resistor to achieve a gain of 4. Feel free to use a different resistor to get to a particular gain you need. However, any change in gain must be compensated for in the JavaScript of the webpage.
The other part of the circuit is a leaky peak detector made with a diode, resistor and capacitor. Its purpose is to translate the AC wave peaks into a DC voltage level. The 47k resistor causes the leakiness. Since the voltage level updates 60 times per second, adding that resistor increases the system's response time.
The potentiometer is used for offset calibration. I used a 15-turn pot for the best accuracy. To calibrate, power the circuit, make sure the AC clamp is not on any wire and measure the circuit's voltage output.
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2) In most places, the Meter is OUTdoors (where it can be easily read), while the breaker box is INdoors (where it is difficult for you neighbors to tamper with).