Hey group, so some advice on the internal vs external power, im converting a Multi-cam cnc router to our loved ddcsv. to original control is from 1998 and has to be drip feed... and sucks with fast 3d moves. I've built many CNC mills etc from the ground up but this one im doing more of a conversion reusing 90% of whats there it has nice IMS drives and power supplies and magnetic home switches etc.
So here is my question the drives have a nice 5v supply already tie'd to drive for the opto (3 wire 5v+,step,dir) can I leave the 5v from the PSU and not use the 5v from the DDCSV, as the grounds will still be the same so the signal will be driven low either way. second is the home switches, they are magnetic 3 wire but are tied to the 24v psu will the home input take a 24v v.s the 12V as noted and supplied from the ddcsv, I would hate to need to swap these out for 12v ones, or I can try and source a level converter. Basically, there is a real nice5/12/24v PSU all wired up already in there and am wondering if I can/should use it v.s the DDCSV power outputs and only tie the signals in, my concern is some of the loads such as these 1998 magnetic switches and opto drives may pull more than the DDCSV step down regulator is putting out.
Reading back a bit here about your mill and the power supply question.
Often AC to DC power supplies are fine sharing house keeping duties and will live together just fine sharing grounds. It's done all the time and shouldn't be a problem.
But I see a lot of people that tend to over think level shifting and resort to more trouble than they need. For example, it sounds like you need to shift 24VDC out of your magnetic sensor down to 12VDC?
I would advise you not to try to put 24VDC into a port that expects a maximum of 12VDC. It's likely optoisolated but you'll probably smoke the opto. Just don't do it.
That said, a simple resistor voltage divider is what you need! Two resistors is all that you need in fact. I've seen people suggest opamps at half gain and weird stuff like that which is totally overkill. A lot of parts that only end up going to waste.
I'll let you research the math
but there is a quicker shortcut...
There are voltage divider calculators on the web that will let you input your starting voltage, your desired voltage and whatever resistor you choose for one leg, and it will give your the value for the other. The better calculators will tell you how much power your resistors will dissipate and how much current it will be drawing. Since you are dividing your voltage in two, it's really easy. Just choose two resistors of the same value! But since you are dropping half of 24 volts, you need to pick higher value resistors! Two 100k ohm 1/4 watts would probably be just fine. This will lessen the current draw on your sensor output and dissipate less heat, use less power and save more trees.
Bowden's hobby circuits hosts my favorite divider calculator because it calculates power dissipation and current. And it does the math!
Just use the 24 volt signal output out of your your magnetic sensor and tie it to the top side of the divider, the other end of the divider to ground, and the middle of the divider is now your new 12 volt DC magnetic switch signal. Easy. The grounds should already be shared.
Shifting up would require active circuitry or relying on the higher voltage supply and whatnot of course, but there are chips made just for that, opamps are great for amplifying AC, but a lot of hassle for D.C., just use a purpose made chip for DC shifting, no extra components and oscillation issues.
Sorry if you know all this already, but I see people who could stand to learn that you don't always need a complex circuit to do a simple job that a couple of simple resistors can do!
-Ryan
