| Could be bad breadboard... | | -Adam Good point ! The quality of modern 'solderless breadboards' (called protoboards when I was a young whipper snapper) could be suspect.
I first used these back in the late 70's, and still have those, and they still make great connections. But I bought some newer ones ~2005, and within a year, the bottom fell out, along with many of the contact strips. Check it out. Get your ohm meter out (with the circuit off) and see if you get continuity. Put the one test lead on the pin coming out of your uC (PICaxe, ...) and the other on the 74141 pin where its suppose to go. Do this with all 4 BCD inputs. Also, for other general digital circuit guidelines. I always point people to Don Lancaster's TTL Cookbook. Yes, it was written around 1970, but there are many very good guidelines in it, that apply even today. We've got to find something as concise on the web, that does the same thing. Here are few rules, off the top of my head: (1) Use a good clean power supply. Connect it to your circuit with as fat as traces (or wires) as possible. (2) Sprinkle capacitors across power and ground all over your circuit. Preferably as close to the power and ground pins of each chip as possible. Usually they're 0.1uf (100nf) ceramic capacitors. Some big chips require you to use several near them, so read you datasheets. Chips are fast. Very fast. They can either generate very brief short circuits (in the ballpark of 10nS), and/or be susceptible to these very short glitches on the power rails. Also put a big fat cap (low ESR electrolytic, or tantalum) where the power comes in. Something bigger than 10uf. Watch the polarity of these. If the electrolytic is plugged in backwards, the safety score will split, and goo will ooze all over your board. If a tantalum is reversed, it may catch fire. I'm not a fan of tantalums for this reason. (3) Terminate ALL unused inputs. 'Terminate' means tie it to something. In digital that means tie them to gnd, or power (+5V, ...). Some older chips require a resistor between the input pin and power. TTL chips will internally pull themselves upto a logic-1, but its a weak logic-1. It may be susceptible to interference, and chatter low, intermittently. CMOS, which means most modern chips, basically will float, so you don't know where its going to be. Want a circuit that behaves randomly, just leave a few input pins unterminated. These are only a few of the most important guidelines. And the world has only gotten worse, since the TTL Cookbook first came out. -- 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.
