Ty_Eeberfest wrote: Yep, I recognize the design. See the attachments on Post #1 and Post #7 of this thread:
May not be an exact copy but it's really damn close.
Jeff wrote: I get all misty when I look at the hand tape-up artwork someone produced so very long ago.
wise65vw wrote: Interestingly,the clock appears to share the last 7490 for both hours digits. The 7410 I'm assuming is for the 12-1 transition like on the Texas Instruments design. The other gates are probably used for controlling the tens of hours and the reset on the last 7490. It also looks like this clock uses transistors to take the incoming 60hz signal and convert it to a squarewave pulse. Not sure how good that would be with line noise.
wise65vw wrote: It'd be easier to know if I could see where the diodes are. If they come right off the 60hz output, usually a Zener is used to help square up the output. However, I have seen some methods where two diodes can be used instead of one zener, used to limit the max and minimum signal level to help "snap" the signal to a certain state.One connects to a 5v source at its cathode, and the other diode's anode connects to ground. The signal passes through the middle of them, the point where the anode of the first connects to the cathode of the other and is either pulled to ground or to 5v. They also help with line noise.