Stepper Motor Driver Switching Circuit - Page 1
Forum section: electronics / beginners

author: dave_robinson_022
author_rank: Contributor
timestamp: April 27, 2020, 11:27:30 pm
content: I am looking at a circuit to switch the outputs from a 4 wire stepper motor driver over 4 possible stepper motors (which only one of which will be in operation at any one time).I am thinking that using some kind of DEMUX possibly 2 x SN54HC139 in combination with a PNP transistor or P Channel JFET for each output (as driver outputs 700mA / phase) could work. However this is starting to look a bit messy. Is there a more elegant way of achieving this?

author: oPossum
author_rank: Super Contributor
timestamp: April 27, 2020, 11:34:08 pm
content: The simplest least expensive solution is probably to just use three more stepper drivers. Stepper driver modules for 3D printers are cheap and have most of the necessary support components on the board. Creating an electronic (MOSFET) or electromechinical (relay) switch will probably be more complicated and less reliable.

author: wizard69
author_rank: Super Contributor
timestamp: April 28, 2020, 12:13:18 am
content: I have to agree with the idea of a separate driver per motor. If you have limited I/O I'd consider switching the control (step and direction signals). This can be done in a number of ways so you would have to determine the best avenue.

author: dave_robinson_022
author_rank: Contributor
timestamp: April 28, 2020, 10:04:48 pm
content: That makes a lot of sense; I didn't consider switching before driver. Yes the issue is control boards support for extra steppers. I want to use 3 on Z axis, A and B for motion and then up to 4 on extruders for tool change. As only one tool will be in use at once the I don't need I/O control over more than 1 driver at a time.Without having to concern myself with controlling the power from driver to motor I can just use a Dual 1:4 DEMUX like 74AC139 to switch step and dir pins; that way I only use an additional 2 I/O pins on controller.

author: langwadt
author_rank: Super Contributor
timestamp: April 28, 2020, 11:16:40 pm
content: Quote from: dave_robinson_022 on April 28, 2020, 10:04:48 pmYou don't need to switch the direction pins, the drivers that isn't stepping doesn't care about direction so you can just connect all the direction pins and then you might as well skip the mux and just do three extra step pins instead of two pins for a mux

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 28, 2020, 11:21:05 pm
content: Saw an early 90s "belt and suspenders" version of this. They used a boardchock fullof relays. Weighed about a kilo. (That was a 1-to-16 or 32 selector, I forget exactly what.)Nowadays I suspect you'll find not only is it more compact, it's also cheaper and more efficient to do it with individual controller ICs. At least you'd need some pretty big motors to justify otherwise, but then you'd need bigger relays (or contactors) to boot.Muxing logic is easy; a 1-of-N selector like 74HC138 on the \CS pin and you're set.Quote from: dave_robinson_022 on April 28, 2020, 10:04:48 pmFYI, use 74HC unless you need more speed or lower voltage operation. 74AC is HC beefed up -- essentially the same thing but draws huge shoot-through current, very demanding on bypassing. Similarly 74LVC is very fast, more refined like HC, but also kind of questionable at 5V supply; I recommend 3.3V or lower. (HC is fine on 3.3V as well, if you don't mind a few ns slower speed.)Most likely CD4000 is even fine here, with its 100s ns delays, and 5-15V supply range.Also, true analog muxes are available in both families (CD4051 and relatives; 74HC4051 is the HC family equivalent).Tim