I'd agree with the above. To make sure you are avoiding any indeterminate states, pull all of the inputs up to +5v with a resistor of about 2k2 to 4k7. Then, for the inputs you want low, jumper those inputs to ground. The pull-up resistors will mean you get a good solid '1' without the jumper, and a good '0' with a jumper to ground.
When designing with TTL,back in the day, we tended to work with negative logic as a preference, because of the nature of the inputs being connected to the emitters of bipolar transistors. On Wednesday, 27 September 2023 at 10:14:46 UTC+1 Craig Garnett wrote: > I tried those suggestions and nothing changed, there's around 4ma total > through the LEDs now so it shouldn't be in meltdown mode. > > On Tuesday, 26 September 2023 at 17:45:06 UTC+1 Craig Garnett wrote: > >> Thanks, >> I'll give those suggestions a go. >> >> On Tuesday, 26 September 2023 at 16:05:17 UTC+1 gregebert wrote: >> >>> 74xx TTL devices have a rather high input-low current, on the order of >>> 1mA, so you should use a much smaller pulldown resistor, say 100 ohms, or >>> perhaps none at all. Logically, it should not be possible for more than 1 >>> output to get driven low on the 7441, but that only applies if all >>> parameters in the datasheet are met. I suspect that the 100K pulldown isn't >>> really pulling-down to a logic-zero, and the IC has gone to some >>> intermediate logic state which is non-deterministic. >>> >>> For the LEDs, I would recommend having a 2K series resistor and driving >>> from +12 VDC. That works out to around 5mA of current which is enough to >>> make many LEDs visibly glow and well-below the 7mA max current rating of >>> the 7441. >>> >>> On Tuesday, September 26, 2023 at 6:30:15 AM UTC-7 Craig Garnett wrote: >>> >>>> I bought a 74141 on Ebay and I had a bit of trouble with the delivery >>>> but it arrived eventually so I'm trying to test it on the breadboard. >>>> >>>> I've hooked up LEDs from +ve to all the outputs and pulled the 4 >>>> address lines down to ground with 100k >>>> >>>> When I power it up 6 of the LEDS are on and raising any of the address >>>> lines does nothing. >>>> >>>> It doesn't look good does it? >>>> >>>> Craig >>>> >>> -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/6caa8908-2581-43d9-8f44-f8def128e3b3n%40googlegroups.com.
