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Clock: A Good Time

A project log for DDL4-CPU

A Modular 4-Bit CPU Design

daves-dev-labDave's Dev Lab 05/25/2018 at 23:130 Comments

So the Clock Generator Module is assembled! Well... this is actually the second one I assembled. Last night I finished the first one and cleaned it in my heated ultrasonic cleaner, and then placed it in my reflow oven to dry it off. I have a pre-programmed "dry cycle" that heats the board to 105C for 2 minutes to dry up any moisture left on the board. Unfortunately, I wasn't paying attention and set it for a full "lead-free reflow cycle". I can back to check on the board just in time to smell plastic. After a cool down, I inspected the board.... every piece of plastic was melted... the buttons, the barrel jack, and the switches. In addition, it had reflowed the parts and there were a bunch of shorted pins! So I eneded up building another today. The Clock Generator Module was originally tested as part of the Digital Design Doohickey, and has basically remained unchanged, with the exception of added a reset button with a Schmitt trigger. The core is based on a 555 timer, and a Single-Pole-Double-Throw(SPDT) switch that lets me select a predefined clock rate of 2Hz or 10Hz. There is also a SPDT that allows me to use a step button connected via a Schmitt trigger to manually pulse the clock. A standard 2.1mm barrel jack provides a +5V input. I have a LED to indicate system power, and for the system clock pulse.

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