On 2/15/2014 5:12 PM, [email protected] wrote: > I'm aiming to use a Beaglebone Black to measure some voltages. I have > no problems with sorting out voltage dividers etc. to get the measured > values down to less than 1.8 volts but I'm not so sure about how to > protect the inputs against transients and at any time the Beaglebone > isn't turned on. > > Firstly, what's the usual method for preventing transients getting > into the Beaglebone inputs? This will be a moderately noisy > environment (a boat with 12 volt car style electrics). > > Secondly how do you ensure all the inputs are off until the Beaglebone > has come to life? The measured voltages are going to be there 'all > the time' regardless of what the Beaglebone is doing so there has to > be some way of preventing the input being actually presented to the > Beaglebone until it has powered up. Is there a standard (and simple!) > way of doing this?
There are a variety of chips designed to facilitate hot-plug or live insertion that would probably work. See for instance the various CBT products from TI and others, which are low-resistance pass transistors when on, and open circuits when off. They can be used to prevent damage when the power is off, provide voltage level translation, and in a variety of other ways. As an example, something like the following ought to work: http://www.ti.com/product/sn74cbtlv3861 Alternately, you could put an op-amp filter/driver circuit in front of the ADC inputs, powered by the ADC 1.8V rail. Then you have to protect the ADC inputs, but typically there's a series resistor as part of a filter circuit so you don't have to worry about exceeding the devices maximum clamp current. There are many other ways to do this as well. One of the fun things about engineering is there are so many different ways to solve the same problem. -- Charles Steinkuehler [email protected] -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
