RobG 1,892 Posted July 31, 2011 Share Posted July 31, 2011 Here is a little LED Display Booster pack (a.k.a. Shield) I have created for LaunchPad. It has 2 595's, uses 3 wires to communicate with LP, and supports both, common cathode and common anode displays. All LP's pins are accessible on the shield, any pin can be used to drive the display. Four unused 595 outputs are also accessible. Transistors are MMBT3904 NPN for CC (R14 0ohm and R13 empty) or MMBT3906 PNP for CA (R13 0ohm and R14 empty.) If interested, bare boards are $4 shipped to continental US, 2 for $6. bluehash, pine, gwdeveloper and 1 other 4 Quote Link to post Share on other sites
cde 334 Posted August 1, 2011 Share Posted August 1, 2011 Nicely done. Are the 595's outputs also available on the header? If not, wouldn't it be nicer to have a (pair) BCD to dual 7 segment display controller? Quote Link to post Share on other sites
RobG 1,892 Posted August 1, 2011 Author Share Posted August 1, 2011 Unfortunately not. Parts are mounted on both sides and there's not much wiggle room, but I will think about that. Quote Link to post Share on other sites
zeke 693 Posted August 1, 2011 Share Posted August 1, 2011 Are the 595's and NPN's SMD parts? Quote Link to post Share on other sites
Mac 67 Posted August 1, 2011 Share Posted August 1, 2011 Hi Rob, Looks nice. May I ask if you've built a prototype and characterized it yet, please? I'm curious about duty cycle (25%), peak and average current per segment, and perceived brightness. Thanks Quote Link to post Share on other sites
RobG 1,892 Posted August 1, 2011 Author Share Posted August 1, 2011 Are the 595's and NPN's SMD parts? Yes, all SMD. Transistors are MMBT3904 NPN for CC (R14 0ohm and R13 empty) or MMBT3906 PNP for CA (R13 0ohm and R14 empty.) ...May I ask if you've built a prototype and characterized it yet, please? I'm curious about duty cycle (25%), peak and average current per segment, and perceived brightness... I have a prototype but I don't have those specifics yet. Peak current is limited by 595, display's pulse forward current is 150 mA and DC forward current is 30 mA. Displays are very bright, at 10mA typical luminous intensity per segment is ~80 Mcd. Quote Link to post Share on other sites
cde 334 Posted August 1, 2011 Share Posted August 1, 2011 Unfortunately not. Parts are mounted on both sides and there's not much wiggle room, but I will think about that. Ah. Didn't see the schematic before. The displays are multiplex, so require scanning to display all 4 digits. Hmm, at the least, bringing out the last 4 available outputs on the second shift register would be nice. Either with or without transistors. Quote Link to post Share on other sites
Mac 67 Posted August 1, 2011 Share Posted August 1, 2011 Rob, what kind of power can you get from the Launchpad board? Does USB give it 500-ma or 100-ma? Is the Launchpad regulator 3.6v at 100-ma? Sorry for all the questions... Quote Link to post Share on other sites
cde 334 Posted August 1, 2011 Share Posted August 1, 2011 Rob, what kind of power can you get from the Launchpad board? Does USB give it 500-ma or 100-ma? Is the Launchpad regulator 3.6v at 100-ma? Sorry for all the questions... I've gotten nearly 500ma out if it (lcd + backlight nearly 400ma). Depends on if computer is strict with usb standards, does the 100ma blocks regulation (100,200,300, etc as requested) or does just 100 or 500, or does just 500, or if it is a high current port that does more. The regulator is TI TPS77301 Single Output LDO, 250mA, Adjustable(1.5 to 5.5V), Fast Transient Response, SVS Quote Link to post Share on other sites
Mac 67 Posted August 1, 2011 Share Posted August 1, 2011 cde, If it's a 250-ma regulator, wouldn't that imply that you're not going to get more than 250-ma from it? How could you have gotten nearly 500-ma from it? Quote Link to post Share on other sites
cde 334 Posted August 1, 2011 Share Posted August 1, 2011 cde, If it's a 250-ma regulator, wouldn't that imply that you're not going to get more than 250-ma from it? How could you have gotten nearly 500-ma from it? LCD and Backlight were being powered from the 5v TP near the usb connecter. So powered from the usb port. Only thing I had on the 3.6v regulator side, is the g2232. Quote Link to post Share on other sites
Mac 67 Posted August 1, 2011 Share Posted August 1, 2011 What I'm trying to figure out is how much brightness you can expect from Rob's design. It looks like he's using the LaunchPad 3.6v supply for the 74HC595 drivers and for the LEDs. If Rob can get 250-mA from the supply then it seems the 74HC595's will be the limiting factor, as he said, because if he could get 30-mA from each 74HC595 output (is that even possible?), he would need 240-mA to light all eight segments of a single digit at the same time. I'm not sure a 74HC595 output can supply 30-mA "peak" current to each segment at 1/4th (25%) duty cycle, but if it can, you can expect the same brightness level that you'd get by supplying the segments with 7.5-mA "average" current. So I guess a slightly more refined question would be, how much "average" current (brightness) per LED can you get from Rob's design? 3-mA? 4-mA? Quote Link to post Share on other sites
RobG 1,892 Posted August 1, 2011 Author Share Posted August 1, 2011 This is pretty much it. Quote Link to post Share on other sites
RobG 1,892 Posted August 2, 2011 Author Share Posted August 2, 2011 Here are my almost finished boards, first board as described in the original post, second board requested by cde with remaining 595 outs and P2.0-P2.6 broken out. I have little cleanup to do and off to Seeed. Quote Link to post Share on other sites
RobG 1,892 Posted August 25, 2011 Author Share Posted August 25, 2011 It's finally here! See my original post for more pictures and the movie. zeke 1 Quote Link to post Share on other sites
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