On Sunday 15 March 2020 23:19:17 Peter C. Wallace wrote: > On Sun, 15 Mar 2020, Rafael Skodlar wrote: > > "... The outputs are push pull CMOS that will drive to the output > > supply rail of 3.3V. This is sufficient for TTL compatibility but > > may cause problems with some types of loads. For example when > > driving an LED that has its anode connected to 5V, in such > > devices as OPTO isolators and I/O module rack SSRs, the > > 3.3V high level may not completely turn the LED off" > > You left off a bit of the manual text: > > "To avoid this problem, either drive loads that are ground > referred, Use 3.3V as the VCC for VCC referred loads, or use open > drain mode." > To further discuss/clarify this, while open drain seems ok in stepper systems. I am very reliably controlling big 40 amp ssr's with open drain outputs, to the - terminal, same for stepper drivers applying open drain to the -input of the stepper drivers while bussing a solid 5 volts to the + terminals. No 3.3 volts exists in the control stuff that isn't internal to the pi's. But I have a drawer full of that stuff, so a conversiion would be fairly easy. Using 3.3 volts and open drain would seem to be a belt and suspenders approach if its enough drive.
So, should I stick a buck supply set at 3.3 volts to drive the + rail to that stuff? Is that sufficient drive for a stepper driver such as a DM542 or its ilk? Ditto the SSR's? And the + rail of the 7i42TA's, they are getting +4.87 volts for a logic high when the ATS667's are off. Ack their specs, they won't work at 3.3 volts. And it makes a certain amount of sense to restrict the 7i42TA + rail to 3.3 volts if it would help clip the noise etc. Thanks Peter. > Peter Wallace > Mesa Electronics Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
