On 3/15/2019 3:42 PM, Shane Roebuck wrote: > Hey guys I have machinekit setup on beaglebone with probotix--bb cape, I have > 24 volt pwr supply hooked to cape and stepper driver, the signal coming from > the cape for direction is little over 4 volts, my driver says it needs 5+ do > I need a voltage step up between the cape and driver? The driver is a Chinese > stepper driver.
The step/dir pins on the Probotix cape are buffered and should be able to directly drive most any stepper driver. The schematic on the Probotix page shows a 74LS244DW used as the buffer. If this is _really_ a 74LS series (bipolar TTL) it will have asymmetrical drive and will be able to pull down better than it drives a high signal (the more modern HC and HCT series CMOS parts have symmetrical drive). So if you're driving an opto on the stepper driver, it may work better to hook it between +5V and the step/dir signal vs. the step/dir signal and gnd. If you do this, invert the pin in your HAL file to compensate. It should work pretty well either way, but it depends on the specifics of your stepper driver. Typical LS Series output specifications for reference: # Driving high Voh = 2.0V (min) at -15 mA Voh = 2.4V (min) at -3 mA # Driving low Vol = 0.5V (max) at +25 mA Vol = 0.4V (max) at +12 mA If the actual part on the cape is really an HC or HCT part[1], you will have symmetrical drive and don't really need to worry about driving high vs. driving low. [1] I don't have a cape handy to check, and it's common to use old LS part numbers on schematics because they exist in just about every vendor's library, and the newer HC, HCT, ACT, etc. families are pin-compatible with the older LS stuff. So just because the schematic says "74LS..." doesn't mean that's the part that gets used. -- Charles Steinkuehler char...@steinkuehler.net -- website: http://www.machinekit.io blog: http://blog.machinekit.io github: https://github.com/machinekit --- You received this message because you are subscribed to the Google Groups "Machinekit" group. To unsubscribe from this group and stop receiving emails from it, send an email to machinekit+unsubscr...@googlegroups.com. Visit this group at https://groups.google.com/group/machinekit. For more options, visit https://groups.google.com/d/optout.
