Well, most TTL parts I've tried will recognize 3.3V. Still not saying it's reccomended. I've never blown a 3.3V input with a 5V signal as long as the 1k resistor is in place. I wouldn't do a commercial design like that, but on the hobby level is a different matter. Will a TTL part even recognize 3.3v as HIGH? I'm usually going the other way, running a strange 3.3v peripheral chip into a 5v CMOS microcontroller. a 5v AVR chip will definitely recognize anything above about 1v as high, but ancient TTL stuff.. Somebody on this list will know, not me.
In my opinion, mixing voltage needs in a design is bad design and should be done sparingly and only if it makes sense. For example: In the Uzebox, there is a 5v microcontroller, a 5v video encoder, & a SDcard. SDcards are 3.3v. However, this works fine because SDCards are low current (the separate LDO linear regulator looks like a transistor). The 3.3v outputs from the SDCard need no voltage translation to the microcontroller inputs and the microcontroller outputs need simple resistor dividers to talk to the SDcard inputs. Why are you using the particular microcontroller that you are using? Part of design should be to look at the voltage requirements of all of your devices and decide if the components you chose make sense. If the 74141 was the critical component, select a 5v microcontroller. If the 3.3v microcontroller is the critical component, select a nixie driver that will work at 3.3v. :) -Adam On Sun, Jul 31, 2011 at 1:58 PM, Jonathan Peakall <[email protected]> wrote: Disclaimer: I am not an EE and I don't even play one on TV. That said, I have done similar things plenty of times, as my uC of choice is CMOS (3.3V). I would supply the chip with 5V and then use a 1k resistors to the pins of the uC. I have a bunch of stuff running like that and so far have never blown a uC pin doing so. Some things won't work like that but I have never trashed a part trying. However, YMMV and don't cry if it doesn't work or blows a pin. Jonathan -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
