5 volt sensors interface
The large majority of the sensors (modules) one can get these days are 5 volt based. Yet the Propeller is running at 3.3 volts,
So I am assuming that all the I/O pins are also 3.3 volt logic based. I didn't see anything stating otherwise, hopefully I missed
something.
So now if we are going to use these I/O devices and sensors it implies that we will need to do a lot of level shifting.
I am not looking forward to the extra H/W on my circuits to do this for all those I/O pins. How is Parallax addressing
this to help the user community?
Jeff
So I am assuming that all the I/O pins are also 3.3 volt logic based. I didn't see anything stating otherwise, hopefully I missed
something.
So now if we are going to use these I/O devices and sensors it implies that we will need to do a lot of level shifting.
I am not looking forward to the extra H/W on my circuits to do this for all those I/O pins. How is Parallax addressing
this to help the user community?
Jeff
Comments
As an input, a 1K-10K resistor will provide needed current protection from a 5V device.
-Martin
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Martin Hebel
Southern Illinois University Carbondale - Electronic Systems Technologies
Personal Links with plenty of BASIC Stamp info
StampPlot - Graphical Data Acquisition and Control
For 1 and 2-way traffic a real level shifter could be used. Like one of these 3 chips:
SN74LVC8T245
GTL2010
ADG3308
NO DIP format that I can find. This world is not getting hobby friendly
Regards
Tim
You'll have to do a little NEWTHINK, but it's really not such a problem. For example,
I2C works fine at 3.3 v. Just make sure the pullups go to +3.3v, and maybe use slightly smaller resistors.
Proper I2C device interface with the clock and data lines as open collector (thus the pullups). They don't power the lines.
Many CMOS devices likewise will work just fine at the lower voltages. I use 8 Pin Pic chips al the time at 3 v. with no problems,
Likewise Sharp IR sensors and lots of other stuff. A good example is the 24LC256 used for the Propeller memory- It'll run at either voltage.
In fact, circuits are more forgiving with regards to overcurrent at those levels. I'm not saying you should do it, But it is possible to run an
LED right off a PIC pin with no resistor and not sustain any damage at 3 v.
The transition is pretty easy. Datasheets for devices will get you started, and if you are stumped, here's the place to ask..
I look foreward to running projects off of just a single lithium battery.
Larry
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Some 3.3v devices are 5v tolerant, other not.
The chip designer is the only one that should specify the max specs.
Now for 5V analog signals, a resistor divider must be used to maintain the linearity of the signal.
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1+1=10
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Jon Williams
Applications Engineer, Parallax
Jeff
module to minimize this interfacing will be provided by parallax?
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Jon Williams
Applications Engineer, Parallax