> Thanks John, > > I would never have figured that out! > > For anyone else reading this thread in the future here's a link that > discusses what John mentions above. I found it using the new knowledge > (pull down resistors) from John's post. > > http://www.msilverman.me/2010/06/z573m-nixie-tube-and-arduino-counter/ > A note on pulldown resistors with TTL. Old standard TTL draws 1.2mA on the input when pulled down. A valid logic-0 needs to be 0.8V or lower. A quick and dirty calc shows that 0.8V/1.6mA=500 ohms. So your pull down needs to be at most a 470 ohm resistor, or smaller. For your test, you can safely, just ground all of your BCD inputs, without harming the chip. No resistor needed.
Get yourself a copy of Don Lancaster's TTL Cookbook. Its all explained there, in a hobby friendly fashion. Its the same info given in old TTL databooks, but you don't need to be an engineer to interpret the info. TTL compatible: Input: logic-0 0.8V max, logic-1 2.0V minimum. Output: logic-0 0.4V max, Logic-1 2.4V minimum. Standard (no S, LS, ALS, H, ...) inputs draw 1.6mA when presented with a logic-0, but only ~40uA when presented with a logic-1. The inputs naturally drift high (logic-1). If unconnected sit ~1.6V which is in 'no-mans' land, though still look like a logic-1 to the chip. NEVER LEAVE ANY INPUT UNTERMINATED ON A DIGITAL LOGIC CHIP. Tie it either to 0 or 1. Pull ups are most common, since they tend to be a high value which can be dragged low easily, by chips of the same family (ie TTL driving TTL). This is even more important on MOS chips (CMOS, uCs, ...), since those inputs are high impedance, and tend to float in neither direction. They're also more sensitive to static. -- 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.
