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Topic: AC Voltage & Frequency Monitor Project (Read 7 times) previous topic - next topic

chrismyers81

I know that this thread is really old, so no one may be watching it anymore, but I thought I'd ask anyhow in case someone was ^o^

Out of random curiosity -

Is the transformer for this 9v with the center tap at 4.5v? Or is it 18v with the CT at 9v? Or is it 36v with the CT at 18v? It looks like the main voltage gets applied to CN4, and is AC, while the CT voltage would be applied to CN3, and be DC, correct?

Also, are my assumptions here correct about the connectors on the schematic?
CN1 = voltage measurement to arduino board
CN2 = frequency measurement to arduino board
CN3 = 9V in (top pin is +9v, center is ground, bottom is -9v)
CN4 = AC in (9v?)

Thanks much!

raschemmel

That's funny , I was going to ask the same thing but when I read your post you answered all my questions.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,
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chrismyers81

Lol...don't take my assumptions as final on it; I'm not anywhere remotely an EE, and only a beginner when it comes to circuit design, so I may be totally off-base ;)

Hopefully someone "in the know" can validate/contradict my interpretations of the schematic, and also be able to confirm the AC voltages that the system is expecting to have as inputs :)

chrismyers81

OH - and, for someone who does know circuit design, I'm hoping to implement something like this on an Arduino Due most likely (through an UDOO.) However, the Due only supports 3.3v GPIO. What all would I need to do to make it properly output for 3V3 GPIO rather than 5V? (short of using some sort of level converter, unless that would be required...)

raschemmel

I have a BSEET (Bachelor's of Science of Electronic Engineering Technology, or Electronic Engineering Technician degree)
but sometimes I'm too lazy to read the fine print....
There is also a CN5 (+5v for frequency measurement).
Here's his two inputs:
Code: [Select]
byte inpulse=2; // square wave input digital  pin
byte voltpin=1; // Vout input anaalog pin 


I think a V/F converter with step-down resistors would be simpler but I guess this works.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,
DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

raschemmel

You can use resistors and diodes (see photo attached).
Are you talking about sending signals from Arduino to GPIO or GPIO to Arduino ?
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,
DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

chrismyers81

Haha, I guess my noob-ness is coming out - I thought that GPIO was just the output pins of the Arduino?

Thanks for the voltage limiter diagram too :) I'm planning on building a GPIO protection board with zeners that I can put inline with any sensors I use, so I'll probably try to build a 5v->3v3 converter board as well, because I can see that coming in handy.

When I was a kid I was super interested in electronics, especially because my dad was an electronics technician. When I got a bit older, I started digging into computers a lot more, and ended up making my career (thus far at least) related to that (linux sysadmin/java developer). But even though I didn't really do anything with electronics, I never really lost the interest in them and in how stuff works. When I bought a house, I started wanting to be able to keep tabs on stuff when I'm away (make sure the heat is working, the basement isn't flooding, the power is staying on, etc.,) and wasn't sure how to really do that short of spending a small fortune on a commercial environmental monitoring system. But then they came out with the Raspberry Pi and I became really intrigued. And as I've been doing more and more research into things, I've started to want to actually start doing something with that interest, which is what got me to looking at Arduino. I'm thinking about doing an udoo because I want the system to be standalone (so that it can keep functioning if the power goes out, etc.) The "watching for a power failure" (so I can know if I need to leave work early to hook the generator up) is what got me to this thread :)

Yesterday I found this article which appears to do the same basic thing (just voltage monitoring, not frequency as well, but I don't really care about monitoring the frequency so much,) but is a lot simpler design:
http://openenergymonitor.org/emon/node/58
They also have a "stepped up" version using an opamp for more accuracy:
http://openenergymonitor.org/emon/buildingblocks/acac-buffered-voltage-bias

And they have what seems like a good article on the "why's" and "how's" of how it: works
http://openenergymonitor.org/emon/buildingblocks/measuring-voltage-with-an-acac-power-adapter


raschemmel

What is your use of the term "GPIO" ?
To me it means "General Purpose Input / Output"
I realize that all of the Arduino I/O falls into this category but no one here refers to it as "GPIO".
They just refer to it as analog I/O or digital I/O or just Arduino I/O, since adding the "GP" is really redundant.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,
DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

chrismyers81

Cool. General Purpose Input/Output for me too :P I was generically speaking about the pins on the Arduino, in this case one of the analog input pins. I'll keep that in mind as I dig deeper into stuff and ask questions, so that I can make sure to ask the right ones :)

Thanks for all your help, input, and feedback so far!  8)

raschemmel

That's a novel use of an opamp as a voltage follower to bias the monitored voltage to the midpoint for
the Arduino input.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,
DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

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