Working progressively: Part III (Breadboarding it)

Posted Sun, Feb 27, 2005 at 06:50 PM

Trucking along from Part II...

Click on any of the above for a larger image.

Some things to note:

1) I couldn't find any stores that sold transistor arrays downtown so I ended up doubling up on PN2222A transistors to create a "darlington pair".

Hence, the need for spilling over onto two breadboards. I did order some (TD62783) online though so the next version should be much smaller.

2) Sorry, I forgot to put on the diagram that the resistors used with the darlington pair are 1K resistors (brown black red). (Nevermind... Go Photoshop!)

3) PN2222A transistors are NPN transistors. They are triggered when they receive a "HIGH" (5 volts) from the Basic Stamp and they are connected to the positive rows.

In electrical jargon, that means that they are providing the "source" for the LEDs -- thus creating a "common-row cathode matrix" configuration.

How I have it set out so far works but I have one article tell me that I only need the source (or a "sink" if I was to connecting it to the negative leads)... and then I have other articles/people tell me that I need both a sink and a source.

I will need to get this sorted out!