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How to build your own homebrew computer: Make a prototype

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So you've scoured the internet and found just the right schematic for your first homebrew computer. Now you want to build it yourself and are wondering how to go about making the circuit. There are many options but three very common approaches you might consider. Let's pick this one for example:

http://z80.info/gfx/z80test.gif

The first and probably easiest is to use a breadboard. These are simple devices you can get from Radio Shack, Jameco, or many other electronic vendors. Depending on your circuit you may need several to fit all your components. I use a small 10" x 10" piece of plywood with several breadboards connected side by side. Here is one from Radio Shack:

http://www.radioshack.com/product/in...ductId=2734154

You follow the circuit and use 24 gauge solid core copper wire to make the connections. I like to reuse old Cat5 Ethernet or telephone wire scrap since it is cheap and effective. You'll need a wirestrippers to pull off about 1/4" of insulation. Put the ICs in the center all facing in the same direction (the notches or dots on the same side) and connect the wires along the holes extending out from the pins. Normally the power supply voltage and ground rails are plugged into the outer rails with some bypass capacitor (typically 10 uF electrolytic) across them.

Breadboards work fine for temporary circuits but you'll soon notice their many limitations. For one, they are small so don't lend themselves to complex circuits. There is a lot of capacitance between the pins so the circuit generally has to be slow (4 MHz or less). Also the wires will start to pile up and get messy. Be careful when you add or change wires because if you bump something it can disconnect and be difficult to find. Use your VOM to check and double check your circuit before you apply power to ensure you've got it connected properly.

While investigating various 6809 type simple computers like these I used breadboards to make quick circuits and test them out. Generally they worked fine although they were delicate and a bit finicky. For short term investigations they work fine. I like to use them for small circuits like PIC or testing various logic combinations or even testing a component.

http://www.sbprojects.com/projects/n...2/nano6802.htm

http://www.anynewgizmos.com/simon680...simon6809.html

Building prototypes with breadboards has its benefits but a lot of problems too. Using a breadboard is a great way to get started since it is cheap, easy, and a whole lot of fun to get that first circuit working! Next time we'll discuss using prototyping boards for point to point soldering construction.

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