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Monday, October 31, 2016

Breadboard computer - experimenting with switch board

I got my first delivery of parts, and I wanted to try testing if breadboard is a viable alternative to soldering, starting with switch board. The idea is very simple:

  • power lines on top of the breadboard are connected to +5V
  • power lines on bottom of the beadboard are connected to GND
  • there's direct connection from GND to bottom of every switch, using 8-wire cables
  • there's individual 8-wire cable with output from every line
  • there are individual resistors (I used 220 Ohm) connecting top of every switch with power line
Here's a quick electric diagram of each of eventually 7x8 output lines:
I can already see weakness of this design - I have 56 resistors to connect (7 switches of 8 each), but there's only 50 lines (10 groups of 5 each), which forces connecting them to lines under each other. As resistors have long leads, they end up touching each other, so testing shows that that this is already not working properly.

Possible solutions:

  • get resistors with common terminal (like 8 resistors with common terminal), so that I'd only need 7 connections to power lines, not 56 – that was actually my original idea, and what I used in my original (soldered) design, but I strangely couldn't find any on amazon or other sites
  • cut resistor leads to smaller length – might still not be enough
  • use second board for just resistors, connect them like DIP elements
  • use fewer switches per breadboard to reduce crowding - it will still be awkward due to inconvenient 5-grouping on power lines, but presumably if I only had 5 switches, I could use two 5-groups per 8-switch
There's one more minor issue - on these breadboards power lines are broken in half, so if I connect them I'd only have 93 out of 100 connection points (1 to get power in, 3x2 to connect the lines) and some extra awkward cabling.

The plan right now is to have a working switch board (doesn't necessarily have to be 56-wide, 40-wide would be fine), and a diode-board. These were invaluable debugging tools during my first attempt.

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