The beginnings of the project started HERE. Will create a new thread when I have something of interest to show. Doesn't belong in this thread though, though it will involve clock(s) of some form at some point. (Graphical LCD on the front panel)
Well, the interesting thing to note here, is that RGB LEDs are not cheap. After doing some looking, about the average price (for surface mount or through-hole 5mm RGB LEDs) is $1.59. If I figure 3 dots per segement, that's 21 LEDs for a single digit, and 84 LEDs for a 4 digit clock, adding 2 more for second dots, comes to 86 LEDs. That runs about $137! If I could get the same digits represented in 3 8x8 RGB matrix panels, I can get that for about $10 less...not to mention, I would then have a matrix display...I'll have to do a little drawing, to see if that would work out okay, but I may just end up going with the 8x8 panels. Anyone know of a cheaper place to get them, than the $43 that LEDtronics wants?
You'll be lucky to get RGB panels any cheaper than that, but for 5mm RGB leds, it may be worth looking on ebay at the ones from "jeledhk".
Thanks Stevey. I'll take a look at those when I get home. The nice thing about using 7-segment displays, is that the circuitry (for the 8x8 panels: 16 outputs + 3 PWM for RGB + 2 for panel select) and LUT in the PIC would be simpler. If I only wanted to hook up to the "LEDs of interest" to make a clock using the 8x8 panels, then it would be the same as a 7-segment, but seems like a waste of the 8x8 panels...
Hi guys...Hav a question about 7-segment displays. What is the lowest-valued resistor u can use to connect the segments to ground in a common-anode 7-seg display? I'm guessing that by using a low-value resistor, u lower the life of da segments inda display... has someone tried this? Cheers.
I'm not exactly making an LED clock here, but I am trying to multiplex some 7-segment displays. I am having problems with the transistor switches used to select the displays. To drive the segments, I am using a darlington transistor array (ULN2001A) and that part seems to work fine. But to select each display, I am using PNP transistors (PN2907). However, my displays are just staying on all the time. My input to the base of the PNP's is the output of a PIC chip, which can only supply 5V. However, I need a higher voltage to drive my displays, so the emitter of the PNP is connected to a +12V. I realize that to actually turn the PNP off, the base needs to be raised to +12V, which the chip output cannot do. Is this the reason why Turbokeu ended up replacing his digit select transistors with the TD62783A (or UDN2981A) High Side Voltage Driver?
Your PNP's are on all the time. You can easily fix this with some NPN's in open collector or cascode configuration to turn on the PNP's. Whichever works best for you
Yes. As SteveyG says you can easily fix this with some NPN's in open collector or cascode configuration. An example here: See T1 to T6. CD
ok, this is a really noob question on transistors: wouldn't you need a resistor in series with the base of the npn transistors T1, T3 and T5 because they are transistors (which switch on current) and not mosfets (which switch on voltage)? i'm obviously missing something, can someone explain this to me?
Crazy idea Wonderful and crazy one. i was planning to do dot matrix but not like this one. Where can get a schematic for small one , Im designing some one like 20*50 but the problem is how to make it a matrix using transistors 2n2222 or any transistors to have a good one thanx
What microcontroller are you planning on using? The schematic can be very simple - 20 PNP transistors driving the rows of LEDs, 50 NPN transistors driving the columns of LEDs and your choice of parallel latches, serial to parallel converters or whatever other mix of components you can think of to drive the transistors from your available number of output pins on your micro. You can make it even easier if you use maxim's matrix LED drivers along with an IIC or SPI interface to your micro.
SteveyG you should really do a write up on that display it is really fantastic and id love to know how you got all the usb interface working and the power supply is immense!
I ordered 8 red and 8 green 8x8 matrix blocks from ebay for £1 each which I'm planning on building two clocks/thermometers/calendars with in the near future. Obviously they'll be on a smaller scale so easier to write up / easier for someone else to reproduce. I have a bit of a backlog of projects going on at the moment though, I should probably finish the ones I've made PCBs for but not programmed. The usb interface was made with a USB enabled PIC (PIC18F2550?) operating as USB to serial converter - pretty much the same as the demo Microchip offer, but with CRC and Checksum on the serial side. Nothing fancy!
This thread inspired me to also construct a 4” LED clock. Many hours later I have it working. My thanks to all the contributors to this thread – I did not need to ask any questions as all the information is right here. My Clock uses the following: 6 x 4” Kingbright displays (SA40-19SRWA), PIC16F887, DS2003, TD62783AP, DS1307, I have added an IR remote control for setting the time and alarm – using a PIC12F675. Code was developed in SourceBoostC. Kind Regards
I've decided to have a go at a copy of the sparkfun clock. Progress is slow (because money's tight!) but here's where it's at so far: Our digit template. That's 4x A4 sheets stuck together. The template was put on to cardboard, and sketched on to polystyrene sheets. We copied this 6 times to show hours, minutes, and seconds. There'll be two colons eventually to seperate them. They'll flash every second too. I picked up 300 blue LEDs for £20. Each "segment" of the digit will have 6 LEDs. That's 42 LED's per digit. 252 LEDs in total. Here's the first run: My phone can't handle the brightness. It's insane. Nearly 0.2 amps for 6 LEDs. That's 1.4amps per digit, which is over 8amps total at 12v. So far I've built one digit, without the perspex front. Here's progress: Planning on running it off a PIC16F628 - just need to dredge up the little bit of micro programming I learnt 6 years ago! More to follow, as I get time and money. Any suggestions on diffusing the blue LEDs without dropping too much light gratefully received!
haha, thats awesome. maybe buy some blue tissue paper to diffuse the leds? the only problem i could see with that is that it would look "crinkly" (for lack of a better term), but maybe you could glue it to tighten it up somehow. what are the exact dimensions on one of those digits?
