Can somebody point me in the right direction with this? I want to measure the current passing through multiple circuits and display on an LCD. I've read about putting a resistor inline with the circuit and calculating the current based on the measured voltage. I want to do this for multiple (8) circuits and would like to keep them separate. What's the best/easiest way to get this done?
Thanks!
Maybe a way to isolate the circuit from the arduino?
use an optocoupler, the intensity of a led shines on an LDR or photodiode which resistance can be measured. YOu only need to make some hardware that controls the led in a well known way. Preferably linear because that would be easy to map() - for non linear there is multiMap - Arduino Playground - MultiMap -
You can also let the frequency of pulses change and detect that. This can be optical like above or maybe magnetic with a reed switch or a hall sensor.
just thinking out loud ...
Thanks for responding. I'm a total noob with this so I'm not sure I understand what you're suggesting exactly. I'll do some research based on your suggestions. Ultimately I don't want the power supplies to share grounds.
Why not use a shunt resistor in each line and calculate based on voltage across the resistor?
V/R = current
Use some DPDT relays for isolation & automated switching control.
Depending on the currents involved, a current transducer may also be an option. What's nice about them vs other methods is that they're non-contact. That helps with safety. The only downside is that you either have to know the voltage or make an estimate thereof to actually get power. Seeeed, iteadstudio and other like vendors now offer current transducers at pretty unbeatable prices.
CrossRoads:
Why not use a shunt resistor in each line and calculate based on voltage across the resistor?
V/R = current
dipmicro electronics
Use some DPDT relays for isolation & automated switching control.
This is the method I was looking at using but with multiple power supplies would it be important that they would all be connected to the arduino ground pin? That's why I wanted to isolate them from each other.
Think about how you use a multimeter - you just have 2 leads, the meter is 'floating' and only connected to what is being measured.
Use the relays the same way.
Connect all the Commons from one side of the shunts to arduino GND.
Connect all the Commons from the other side of the shunts to an arduino analog input.
The Normally Open side of relays connects to the shunts.
The Normally Closed side is not connected.
When you want to make a measurement, drive the coil for 1 and only 1 relay. The arduino GND and Analog inputs are now connected to the 2 sides of the shunt and you can take a reading.
The Arduino GND is not connected to the rest of the circuit so it can act like a floating multimeter.
As nice as shunt configs are, I prefer either power measurement ICs (like the Allegro gear) or current transducers (itead, Tamura, et al) To me, isolation is of key importance to Arduino longevity and ultimately user safety (depending on the currents involved). Allegro ICs are offered with current ratings up to 75A, several folk make evaluation boards for around $20 or less. The current transducers offered by iTead are even less expensive but inherently safe and isolate the Arduino 100% from transients, over-voltage, etc. And they're super-easy to implement thanks to the work that the openenergymonitor.org people have put into documenting their non-invasive power meter, including a Emon library that does all the heavy lifting for you.
CrossRoads:
Think about how you use a multimeter - you just have 2 leads, the meter is 'floating' and only connected to what is being measured.
Use the relays the same way.
Connect all the Commons from one side of the shunts to arduino GND.
Connect all the Commons from the other side of the shunts to an arduino analog input.
The Normally Open side of relays connects to the shunts.
The Normally Closed side is not connected.
When you want to make a measurement, drive the coil for 1 and only 1 relay. The arduino GND and Analog inputs are now connected to the 2 sides of the shunt and you can take a reading.
The Arduino GND is not connected to the rest of the circuit so it can act like a floating multimeter.
Interesting idea. May I ask why dpdt?
Constantin:
As nice as shunt configs are, I prefer either power measurement ICs (like the Allegro gear) or current transducers (itead, Tamura, et al) To me, isolation is of key importance to Arduino longevity and ultimately user safety (depending on the currents involved). Allegro ICs are offered with current ratings up to 75A, several folk make evaluation boards for around $20 or less. The current transducers offered by iTead are even less expensive but inherently safe and isolate the Arduino 100% from transients, over-voltage, etc. And they're super-easy to implement thanks to the work that the openenergymonitor.org people have put into documenting their non-invasive power meter, including a Emon library that does all the heavy lifting for you.
Thanks for the idea. I'll be reading up on this tonight.
