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 > > > >> The simplest solution I can think of is supplying both chips with 3.3V >> and hoping for the best. Altough I don't read russian, I can tell from >> the data sheet that the logic levels should match surpricinly well, >> but I cannot tell whether the rest of the circuit functions properly >> with a lower than expected supply voltage. I have limited capabilities >> to test the circuit properly (with nixies, cathode driver and >> microcontroller etc.) and therefore I wonder if anyone at Neonixie has >> used the K155ID1 like this before. I guess that the question is pretty >> generic really; is it possible to run a (early generation) TTL circuit >> at 3.3V reliably? Keep in mind that I don't require very quick >> switching, kilohertz are just fine here. >> >> The next step would be to add a 5V-regulator just to feed the driver. >> In that case, how/do I need to protect the outputs of the >> microcontroller? I have looked into the 'standard' schematics for TTL >> and it seems to me that a TTL input with a 5V supply would tend to >> pull its input high, possibly destroying a 3.3V output. Is series >> resistors sufficient or are transistors needed too? >> >> > -- > 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 neonixie-l+unsubscribe@** > googlegroups.com <neonixie-l%[email protected]>. > For more options, visit this group at http://groups.google.com/** > group/neonixie-l?hl=en-GB<http://groups.google.com/group/neonixie-l?hl=en-GB> > . > > -- 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.
