Breadboard for Timing Electronics

How do you build the electronics for timing, counting and comparing? How can you make it easy to modify? What did I build, and how did I arrange things?

Breadboarding Electronics

The easiest breadboard to use for IC's is the push-down pin array. You just press the hookup wire into the holes, and each group of five holes in a row are connected underneath. It's sold (at a rather high price) by Radio Shack and (at better prices) other places.

My breadboard is mounted on an aluminum box that also carries a 5v supply for TTL. It has sixteen LEDs with Darlington drivers along the right-hand side for debugging logic circuits.

Breadboard Photo

Breadboard Wiring

There are three sections of breadboard side-by-side, with longer thin strips for power distribution along the bottom.

The long gray cable for "timing control output" goes to the business end of the coilgun. It is an eight-wire cat-3 cable leftover from some telephone re-wiring at home. It has color-coded wire assignments of:

Comparator Wiring

There are three 8-bit comparators, each wired to a pull-up resistor block and an 8-bit DIP switch. The wiring gets a little messy in this area, with all the 8-bit buses running around. So here's a diagram showing the pin connections between the chips, and notes about which switch does what. All four comparators are wired like this.

Note the switch is labeled SW8 = LSB, because the engraving on my switch block says '8' but the wiring is connected to D0 which is the least significant bit of the counter.

Note the switch says On = "0", because again the engraving on my switch block says "On" but the wiring corresponds to a logic 0. Sorry if it's confusing, but it seemed easier at the time to orient the switch this way. I trust you will find a more sensible way than I did for this portion!