Hello -
I am working on a project that involves reading the open/closed state on a open collector output (1A @ 28V). This signal conveys whether or not a motor is running.
I am planning on connecting the output pin to a pullup resistor on the arduino and connecting the ground pin to one of the arduino ground pins.
Should I be able to get away with this without frying the Arduino?
bort:
Hello -I am working on a project that involves reading the open/closed state on a open collector output (1A @ 28V). This signal conveys whether or not a motor is running.
I am planning on connecting the output pin to a pullup resistor on the arduino and connecting the ground pin to one of the arduino ground pins.
Should I be able to get away with this without frying the Arduino?
What pin would you use?careful with the amount of current you sink to one pin,arduino pins are not very tolerable and 1a at 28v already sounds problematic to me.
If it's truly open-collector there is no voltage until you supply it, so there should be no 24V or 28V, and the internal Arduino pull-up should be fine. Check the voltage on the collector and if you don't measure anything you're good to go.
If there is already a pull-up you can use a voltage divider (2 resistors) and if it's unregulated add a [u]protection diode[/u].
Or, an optical isolator offers even more protection.
A diode (1N4148) is commonly used between Arduino pin and open collector output of a sensor, with the cathode(ring) on the sensor side, and internal pull up on the pin.
Leo..
If we have this right, and what you have there is a motor [or motor driver] that presents an open collector [assuming NPN] monitor circuit, and your mention of 1A @ 28V has nothing to do with the monitor circuit [very likely it doesn't], then the following circuit probably applies:
R1 is a guess. If that doesn't work, you'll need to try other values.
R2 & D1 are optional and are a precaution to prevent damage to the Arduino due to voltages higher than 5.5V [the max input voltage on a 5V Arduino].
Q1 probably goes low [saturates] when the motor turns on. But, it's possible that logic is reversed. But, that's easy to deal with in the software [i.e. the Arduino Sketch]. Experimentation will tell.
+Vin is simply a voltage between 7.0V and 12V [standard Arduino input power]. Or, the Arduino can be powered from the USB port, etc. but I neglected to include that in this diagram -- since that's standard Arduino fair.
And BTW: that 1A 28V spec might be the limitations on that Open-Collector output. For instance, my circuit, above, connects R1 to 5V, but that voltage could go has high a 28V, if indeed, that's what that spec is. Also, 1A would be the maximum current that open-collector transistor can safely sink.
