RobG 1,892 Posted October 16, 2012 Share Posted October 16, 2012 I got this very cool RGB matrix that is just begging for a Booster Pack. The overall size is 60mm x 60mm, but it should fit on 50mm x 50mm board. Any ideas on how to drive it? My initial thought was to use HT1632C with transistor arrays. Plain shift registers are another option. Quote Link to post Share on other sites
cubeberg 540 Posted October 17, 2012 Share Posted October 17, 2012 If it's common cathode - you should be able to drive the matrix with the HT1632C and different resistors for the different colors. I've used shift registers (I've got a couple of RGY displays from sparkfun), but it takes up a lot of CPU time to do anything except full off or on. Although - I haven't figured out yet (still need to read the data sheet in more detail) is if the PWM control for the HT1632C is by LED, or if it's for the entire display. I like the price you were able to find for the HT1632's - you'd probably have a hard time getting that good of a price on 3x shift registers and a ULN2803. The QFP package might make it a little more difficult as a kit - although I'd be willing to try it. Quote Link to post Share on other sites
RobG 1,892 Posted October 17, 2012 Author Share Posted October 17, 2012 Shift registers should not be that bad. During each second, we have to send 32 bits 2048 times (8 cols * 256 PWM levels.) @16MHz, that's about 7,812 clock cycles between each transfer. We would probably need 500-1000 cycles per transfer, so that leaves us with plenty of time to do anything else. How about on board MSP430 based controller? HT1632C has global PWM, not per pixel, so that would allow 3bit color only. Display has common anode rows and common per color cathode cols, so that would require extra drivers if used with HT1632. About the package, it's a 1mm pitch QFP, very easy to solder. Quote Link to post Share on other sites
touch 34 Posted October 17, 2012 Share Posted October 17, 2012 You could also use a CPLD or FPGA for controlling the matrix, but the problem is that the source/sink current is limited to something like 25mA per a pin, so you'd still have to use the transistors. Quote Link to post Share on other sites
RobG 1,892 Posted October 17, 2012 Author Share Posted October 17, 2012 New idea. For 24 cathodes, use one TLC5947/51 (constant current, PWM.) For 8 anodes, 8 transistors or sourcing array and either shift register or 74HC138 (138 requires only 3 pins and would be perfect for driving PNP transistors.) TLC5952 is another option, but PWM would have to be handled in code. Quote Link to post Share on other sites
RobG 1,892 Posted October 19, 2012 Author Share Posted October 19, 2012 First stab at this BP. It uses TLC5952 & 74HC138, but I will most likely make it also compatible with TLC5947. RETs are used to minimize parts count. The only thing that worries me is power consumption. I will probably have to add a power socket, an LDO, and another transistor for switching current (Iref resistor.) 4 pins are used for columns (TLC,) 3 pins for rows (HC138.) The total cost of parts (sans PCB, the display, and S&H) should be around $3 ($4 with LDO option.) EDIT: Updated image, there will be no LDO, no TLC5947 compatibility, darlingtons instead of RETs, and there will be 2 extra headers, one for constant current control and one for external 3.6V power. BTW, the outer gray border is the display. xpg 1 Quote Link to post Share on other sites
RobG 1,892 Posted November 17, 2012 Author Share Posted November 17, 2012 I don't have 5952 driver yet (and I am too tired to write it now) to show off what this thing can do, so for now just a few pictures. When powered from LP, each LED gets ~6mA. It's not much, especially when you consider 12.5% duty cycle, but at least it works w/o any external power. When external power supply is used, LEDs will be much brighter. xpg 1 Quote Link to post Share on other sites
RobG 1,892 Posted November 17, 2012 Author Share Posted November 17, 2012 3bit color (no PWM) bluehash and johnnyb 2 Quote Link to post Share on other sites
xpg 127 Posted November 17, 2012 Share Posted November 17, 2012 Looks really good. I am playing with the same RGB matrix (I think) using sinking shift registers (TPIC6B595). I have not been able to achieve the same good colors as you do. What resistor values are you using? Quote Link to post Share on other sites
RobG 1,892 Posted November 17, 2012 Author Share Posted November 17, 2012 I am not using resistors, I am using constant current driver. In my pictures, leds are driven at ~6mA, 12.5% duty cycle from LP's 3.6V supply. Here's another one, with PWM enabled. And schematic: Quote Link to post Share on other sites
xpg 127 Posted November 17, 2012 Share Posted November 17, 2012 I am not using resistors, I am using constant current driver. In my pictures, leds are driven at ~6mA, 12.5% duty cycle from LP's 3.6V supply. Doh, of course Quote Link to post Share on other sites
t0mpr1c3 91 Posted November 17, 2012 Share Posted November 17, 2012 Saw this the other day, it uses HT1632C. http://logos-electro.com/rgb-led-matrix-backpack-1/ Quote Link to post Share on other sites
RobG 1,892 Posted November 17, 2012 Author Share Posted November 17, 2012 I was considering using HT1632, but it doesn't have PWM, so all you get is 3 bit color. The only plus is that you don't have to do multiplexing in software. Also, Holtek can typically source only 60mA on COM output (it can sink 350mA,) which means 2.5mA per LED, not sure why they don't have an extra source driver. Quote Link to post Share on other sites
RobG 1,892 Posted April 17, 2013 Author Share Posted April 17, 2013 New board, replaced TLC5952 with TLC5947. 12 bit color is now possible. Available on Tindie. roadrunner84, bluehash and cubeberg 3 Quote Link to post Share on other sites
cubeberg 540 Posted April 17, 2013 Share Posted April 17, 2013 Cool - when are you going to start selling those Want! What's the other IC? Is that how you're handling the columns, or is that all done by the TLC5947? Quote Link to post Share on other sites
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