Do you get such a thing as a sensor that can be permanently connected between the DC power supply and circuit that will feedback (to the arduino) the amps the complete system is drawing ? Kind of like what the ds18b20 does for temperature.
If so, what should I be searching for ( component description or part number ) ?
If you don't mind surface-mount components the Zetex ZXCT1009 is a workhorse that often fits the bill.
For higher currents hall-effect IC's like the Allegro ACS712 are a popular choice.
It depends a lot on the range of currents you're trying to measure.
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It depends a lot on the range of currents you're trying to measure.
Am running 3 voltages from the DC supply : 13.28v, voltage reg down to 9v and also to 5v ( for the arduino itself ). I don't expect the current to exceed 3 amps.
Would be happy (first prize) if I could measure the current on each circuit -- raw DC supply, and after each voltage regulator.
Then I'd use 3 ZXCT1009's on each regulator input. The raw DC supply will be the sum of the 3 so you don't need a separate sensor for that. I'm assuming these regulators are all in parallel? If you have a 9V regulator followed by a 5V regulator then you only need 1 sensor in this string since for a linear regulator, current in equals current out (minus 5-10mA for the regulator itself).
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So if I understand this correctly, I can hook the ZXCT1009FTA up to each of the 3 circuits, and each will output a voltage relevant to the current passing thru the sensor. The maximum voltage this sensor can output to the arduino is 5V ?
Assuming the above is correct, I then need to connect that output to an analog input pin on the arduino and measure the incoming voltage. I assume there is some formula to convert that voltage to an Amps value ?
So if I understand this correctly, I can hook the ZXCT1009FTA up to each of the 3 circuits, and each will output a voltage relevant to the current passing thru the sensor.
If you look at the datasheet for the current monitor, you'll see you need a shunt resistor:
http://www.diodes.com/datasheets/ZXCT1009.pdf
This device outputs a current based on the voltage across the shunt. That current goes through another resistor that develops a voltage for you to measure on the Arduino's analog input.
OK. Thanks for the link.
Being a real newbie at this stuff, I have a few questions :
If I look at the "Application Information" on page 4 :
I don't see anything that relates to the voltage on Vin and To Load. Am I correct in assuming that the resistor ( Rsense ) is just going to create a small difference between the 2, so voltage is immaterial to this - it is the difference created by the resistor that is measured ( as long as I stay in the 2.5v to 20v range ) ?
So from the example, Rsense should be 0.1 ohm and Rout 100 ohms.
The diagram on page 1 does not show what the I-out is connected to. I assume that the bottom line is Ground and the V-out goes to the analog input pin.
From values I see in the example, the analog input will receive 0.1v for every 1A passing through the component. Would this be on a set scale, so 0.2v = 2A and 0.05v = 0.5A ?
Would it not be more practible to change the resistor values to give a V-out of 1v per 1A. The system would definately never draw more than 3A as the glass fuse would blow at that point, and I 'think' the analog input pin can handle 5V.
If so, am I correct with the following calcs :
vSense = 1v @ 1A
rSense = 1 / 1 = 1 ohm
Rout = Vout / ( Vsense x 0.01 )
Rout = 1v / ( 1v x 0.01 )
Rout = 100 ohm.
So using Rsense = 1 ohm and Rout = 100 ohm, the V-out would be 0.1v @ 0.1A, 0.5v @ 0.5A, 1v @ 1A, etc.
pololu has a pair of nice current sensors.
+/- 5A with analog output.
the other is +/- 30A
And the best google search term is probably "high side current sensor" (or transducer).