I am attempting to (output or 'drive') an Adafruit 1.2" high / 4-digit / 7-segment display (this thing pulls about 700 mA) from an Arduino , to display temperatures of up to about 2,300 degrees with an Adafruit Max-Integrated 31855 break-out-board & k-type thermocouple on the input side of the Arduino.
I would LIKE to power (5.5 volts?) the Arduino from the round-pin connector; and then use the USB-port ONLY to 'spit-out' serial data to a laptop (so as to not 'overload' the laptop's (Mac, Linux or Windows) USB chip(s))...
IS this possible ? (like, maybe cutting the + / - 5 volt wires on the USB-cable)? - or is there an easier way?
I would LIKE to power (5.5 volts?) the Arduino from the round-pin connector;
That takes 6.5 to 12V with 9V being about the optimum.
(this thing pulls about 700 mA) from an Arduino
Are you sure of that? I think you will find it does not take power from the Arduino but the Arduino controls the display. The power comes from the supply connected to the display. You might choose to connect this to an Arduino but you should not as you will not be able to supply the current through the internal regulator, it will get too hot.
and then use the USB-port ONLY to 'spit-out' serial data to a laptop
Do you know you will reset the Arduino each time you plug in the USB lead?
or is there an easier way?
The easy way is to wire up your display to the external supply not to any pin on the Arduino.
Thank you for all your considerable help and 'thought provoking' questions... - some answers:
the display ONLY gets it's power from the Arduino - so - YES - the Arduino is pumping-out 700 mils to power the display (amazing!) - but YES - it gets 'hot'!
I COULD - (YES) power the display externally, BUT that would require a second (or even third) cable, in the industrial environment (that I'm working in (soon, probably NOT to be working in!) that's something that could be done; or maybe I just bring-in the power cable into a housing, and split it there, part going to
power the Arduino and another part going to power the display, separately
My Arduinos (I think I have 15-20 of these) I do not 'think' reset - but maybe they do so and I don't know it - that's something that I should spend more time and attention evaluating...
- the 'data-file' that the Arduino Sketch spits-back over the serial (USB) connection doesn't care, either, it picks-up and 'extrapolates' lost-data (there's a routine running on the "laptop" that does this)
some EXCELLENT IDEAS that bear more research and evaluation - thanks - very much - for the ideas!
or maybe I just bring-in the power cable into a housing, and split it there, part going to
power the Arduino and another part going to power the display, separately
Yes that will do.
I do not 'think' reset
Every time you plug a USB cable into an Arduino it resets unless you have modified the circuit to disable the auto reset circuit.