On 8/17/2016 5:26 PM, [email protected] wrote: > I am wondering if a beaglebone black can be used to measure industrial > 4-20 ma loops? I see there is an ADC feature, but the voltage range is > only to 1.8V. Is it possible to set it up to work with the standard 24VDC > circuitry involved with most 4-20ma loops? > > A 90 ohm resistor carrying 20mA will develop a voltage of 1.8V. This is cutting it a little close, so I recommend 68 ohm, which is a more standard/easier to find value anyway. So, just terminate your 4-20mA line with this resistor, and connect it to the Beaglebone analog input. Of course if you're in an industrial environment you need to watch out for transients, noise and interference, especially since the Beaglebone inputs are famously fragile, so include some serious input protection (e.g. four diodes connected as two anti-parallel 2-diode chains, with a filter cap across it and maybe some series resistance). Then again, you could follow evilwulfie's advice to use a dedicated buffer op-amp.
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