Solder smoke

by Chuck September 29, 2010

Occasionally, when I’m buying electronics gizmos, I’ll pad the purchase with interesting little bits of hardware that the supplier has on sale. This summer, when I was buying switches for Katie’s educational display, All Electronics  had some 8x2 LCD displays on sale for $5.50 each. Of course I bought two.

With the two displays in hand I went through my back issues of Nuts and Volts magazine looking for a “Picaxe Primer” column that I remembered, where Ron Hackett built up an LCD driver based on the Picaxe 14M chip. Look in the June 2009 issue for the column, or you can visit his Web site and buy all the parts that you need to build a serial LCD backpack. That’s what I did.

OK, so I didn’t order all the parts. I forgot to buy the 3-pin right angle male header that you need for the speed jumper. That just gives me an excuse to create an order for some other place – and pick up a few new gizmos to play with.

Building the LCD board was a simple and enjoyable job. The only problem I had was with R8. The assembly instructions say “See text” but the don’t say that the text in question is at the bottom of the page describing the LCD board. I eventually dug up the old Nuts and Volts back issue that had the discussion of the LCD backpack to figure out what was going on. Turns out R8 is the current limiting resistor for the LED backlight. If you just leave it off, you don’t need to worry about sizing it…

Anyway. I built up the board, programmed a 14M with the demonstration program, and turned it on. Nothing. Damn. Then I remembered to adjust the contrast pot – a few turns and there was the display flashing merrily away. I downloaded the serial LCD controller, plugged the LCD module into the backpack and the backpack into my breadboard, wired an 08M to send data, and that worked on the first try.


Finally, I ran down to Radio Shack (twice – always make sure that the package you grab out of the parts bin is actually the one that’s supposed to be in the parts bin) for some #2 nuts and bolts to attach the backpack to the LCD module.

The total cost for the two serial 8x2 LCD displays was about $40. At Digi-Key a single Matrix Orbital 8x2 serial LCD is $39.95. I’m sure that the Matrix Orbital display is faster and less “pic-y,” but I’m satisfied with the new ones that I built.



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