Thursday, June 16, 2011

3-Digit 7-Segment Display With an SAA1064

Working on the grinder timer project, I built out a basic circuit (EAGLE .sch) with an NXP SAA1064 and resurrected a test sketch (Arduino .pde) for it. The SAA1064 works beautifully for driving common anode 4-digit 7-segment displays with constant current per segment, from 3 to 21 mA in 3mA increments; in this case I'm only driving three digits since that's what the design calls for.

There are two buttons in the test sketch (on D10 and D11), the first to change count modes (seconds, tenths, hundredths, hex, and "chase") and the second to cycle through the seven current settings.

This schematic is identical to one I did a board layout for with an SO24 package chip, but for some reason those boards didn't work; maybe something in manufacture or assembly bridged pins somewhere. I'll redo the layout and see what happens, with vias further from pads.

Wednesday, June 15, 2011

Minimalduino 105: Nice!

I built out one of the "V.105" boards I got a few weeks ago from the DorkbotPDX PCB order, and it works beautifully, almost identical to the version 107 I posted files of, with "5V/3.3V" voltage and "FTDI/IN" power selector switches. I mounted a mini USB socket and a 7805 regulator, in addition to the barrel jack for power in.

I've gone to whole number versioning btw, no need for "always under 1" versioning or major/minor versions, and if I need to go higher than 999 (huh?!), I can just use four digits.

Top and bottom labeling came out great, including the Open Hardware logo, though the letters mush together a little. Also, the "FTDI" header label didn't print at all, maybe there's a problem having two "FTDI" text labels.

One issue is that the drills for the main female headers are smaller than those on versions 89 and 97 boards, even though they use the same parts in EAGLE! I'll check the parts and maybe swap them out. That's a bummer-- I had to drill them all out to mount the headers, which ripped some of the pads off the fiberglass, but thankfully they stayed connected to the traces.

Minor edits for the next version:
  • Move the power input components to give electrolytic capacitors more room to accomodate shorter/fatter ones or taller ones mounted horizontally. As it is, the 100uF cap at the input is jammed between the .1uF cap and the barrel jack. [done]
  • Rotate LED's so they can be mounted horizontally for better side viewing when using a shield. [done]
  • Add heat sink polygon and vias under the 7805 tab.
  • Fix the Sparkfun mini USB through-hole part: its outline is on the bPlace layer, not tPlace where it belongs. Or just use a different part. [done]
  • Check female header drill diameters.
  • Add 2-pin header at the reset button to make it easier to add a remote panel-mounted reset button. [done]
  • Round the corners; looks nice on the Freetronics boards. Also check Uno outline and drills to make sure things are lined up right. [done]
I'm pretty happy with this for now though-- I have plenty of cheap, homemade, 5/3.3V-switchable Arduino-compatible boards to work with!