Looking a bit more, I believe I should be able to connect one of these step-up regulators to the 5V and GND GPIO pins on the RPi and the other side to a JST to plug directly into the power input JST port on the display’s driver board… does that sound right?
Depends how much current the display needs @ 12V and how much current can be supplied by the RPi output.
As an example 100mA @ 12V needs 240mA @ 5V plus allowance for efficiency which could be 80%. At 80% the 240mA becomes 288mA.
This is all a little bit over my head, but my understanding is that the display can run on anything from 6v to 12v, and likes around 0.5 A + (some variation depending on voltage, but I can’t seem to find the table I was looking at for that…)
It is published in the Tech Specs on Core web site. 12V @ 0.5A or 500mA.
If you plan on using the Step up Regulator previously mentioned or any other step up from 5V the numbers translate to.
12V @ 500mA = 5V @ 1200mA or 1.2A, assuming 80% efficiency you will then require 5V @ 1.44A to power the display.
I don’t know but I doubt the RPi 5V output can supply this sort of current. Even if it could don’t forget the power TO the RPi will have to supply this additional current as well as powering the RPi device.
With all this in mind having 2 power leads may not be a bad option. At least you know it works.
and probably the easiest way to go. Particularly if she who shall be obeyed has decreed one power cord (no “h”) only. I still would advise do the numbers first so you don’t go out and purchase something which will not do the job and finish up being a door stop.
I can see that for a step-up, I would connect RPi GPIO pins to the stepper, then connect the stepper to the power input JST socket on the display.
But for a step-down… I imagine I need to go from the stepper to the GPIO power pins on the RPi, but I don’t know where I could connect from the display to the stepper… there’s no “power out” socket, so I’m guessing I’d need to solder somewhere?
You guess right. At the end of the day to do as you require is going to involve some physical effort re connecting all this together. Unfortunately helping with this remotely is not very feasible. If you are not capable in this you may need someone you know to help.
There are power supplies out there which have dual outputs like 5V and 12V. I am not going to suggest any of these as they involve making 240VAC mains connections and should be done by a licensed electrician and by reading your posts I don’t think you would have the necessary expertise to safely carry out this task. Also this mains connection and low voltage connection are on the same terminal block which adds to the risk of mistakes even though connections are clearly marked.
Your 12v power pack will take input from the mains, and provide 12v. That 12v will power the display directly. Then your 12v-to-5v adapter will take that same 12v supply and convert it down to 5v. The 5v will supply the Pi. A picture will show the arrangement.
So you will need to cut the 12v supply from the power pack to wire in two new leads, one for the display and one for the converter. Then you will need to make a supply wire from the converter to the RPi.
There’s not that much involved. There are splitter cables available, but as the step-down converter is likely to have a different input socket you will likely need to make up at least part of that cabling. But the bits and pieces needed should be readily available. A suitable splitter is: 2.1mm DC Splitter Cable 1 Socket to 4 Plugs | Jaycar Electronics
For instance, if the step-down converter has screw terminals for the input side you could cut off one of those plugs and wire the loose end straight into the step-down converter input. If you select a step-down converter that is designed for replacing a USB source, then it will have a USB connector that you can plug the existing RPi USB cable straight into, such as https://www.ebay.com.au/itm/393230859976
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