they're selling spice, or the woes of affordable smd's
Fred Hawkins
Posts: 997
( I hate my laptop. Especially when my moderately entertaining post disappears when my overlooked thumb does something with the lame touchpad.)
2nd try: RGB LEDs have three leads plus a common cathode or anode. 74hc595's have 8 registers. So every 8 LED's match every three shift registers. Which works on the breadboard, sort of, but in my real world I have visions of rats nests, spaghetti and scary dreams. So today I was wishing LEDs were smarter, and then thought, what if shift registers were dumber?
So, I was trying to work out how to use TI's little logic to make a 3 bit shift register in smd, all the better to drive the pins on my pile of RGB LEDs. (think:·a tiny·pcb with serial input, two or three little chips·dwarfed by a big LED. Serial line plus power lines go off to the next little board down the line...)
Alas, the short end of the story is that while they are small, and they are rudimentary, they sure aren't cheap. Plus I have to buy a reel of 3000. Or maybe 250, if I spend .43 each... Fairchild's tinyLogic was pretty much the same. And Mouser just plain scared me half to death.
Which leads me to my questions: where do real (hobby budget aka married) people get ahold of smds? Does anyone? Or are they the realm of worked out mass produced commerce and best left to the big kids?
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2nd try: RGB LEDs have three leads plus a common cathode or anode. 74hc595's have 8 registers. So every 8 LED's match every three shift registers. Which works on the breadboard, sort of, but in my real world I have visions of rats nests, spaghetti and scary dreams. So today I was wishing LEDs were smarter, and then thought, what if shift registers were dumber?
So, I was trying to work out how to use TI's little logic to make a 3 bit shift register in smd, all the better to drive the pins on my pile of RGB LEDs. (think:·a tiny·pcb with serial input, two or three little chips·dwarfed by a big LED. Serial line plus power lines go off to the next little board down the line...)
Alas, the short end of the story is that while they are small, and they are rudimentary, they sure aren't cheap. Plus I have to buy a reel of 3000. Or maybe 250, if I spend .43 each... Fairchild's tinyLogic was pretty much the same. And Mouser just plain scared me half to death.
Which leads me to my questions: where do real (hobby budget aka married) people get ahold of smds? Does anyone? Or are they the realm of worked out mass produced commerce and best left to the big kids?
·
Comments
-Phil
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'Still some PropSTICK Kit bare PCBs left!
In terms of SMDs, I used both digikey and mouser depending on who has it and the price though I find mouser package SMDs better, each in a separate re-sealable bag.
More is possible, but I haven't figured out the maximum.
If you really want SMD parts, you don't mind dealing with ebay and you're not in a hurry, Sure Electronics (China) may have what you're looking for at affordable prices. I've ordered quite a bit from them and they are reliable but pretty slow on shipping (1-3 weeks). A lot of items ship free if you're not in a hurry.
Below are a couple of examples that could get you started with a good "starter" inventory of SMD 0805 parts.
http://cgi.ebay.com/50-Value-0805-SMD-Resistor-Kit-0R-10MR-5-5000pcs_W0QQitemZ230269751546QQihZ013QQcategoryZ4664QQcmdZViewItemQQ_trksidZp1742.m153.l1262
http://cgi.ebay.com/SMD-0805-50-Value-Resistor-32-Value-Capacitor-Kit_W0QQitemZ230269753316QQihZ013QQcategoryZ4662QQcmdZViewItemQQ_trksidZp1742.m153.l1262
Duffer
Virand: my 'problem' is that the LED's are spaced about 8 inches apart and probably need to be un-multiplexed. Seems like my wiring hassles would get worse if I tried that. Ah well, maybe I can fall back on Suzy Crafty's Hotglue Gun Solution ("if it moves, squirt it") to bring order.
Another option would be to use a small micro to drive each LED. For example, the Atmel ATTiny13 with 8 pins (6 of them usable) can be had for $0.88 each (quant. 25) from DigiKey. Three pins could be used for the LED and one or two for communication on your daisy-chained bus. At this price, it's reasonable to think of such a micro as configurable logic, rather than being overkill.
-Phil
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'Still some PropSTICK Kit bare PCBs left!
Meanwhile, there's this proof of concept: http://www.attiny.com/rgbled.htm
Which suggests that the challenge would be coming up with a smart protocol·that lets the prop set it and forget it.
Post Edited (Fred Hawkins) : 7/16/2008 7:59:04 PM GMT
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Tracy Allen
www.emesystems.com
There are a variety of shift registers designed for use with LEDs like the TLC5940. Thanks Timmoore for the plug! At Brilldea I sell the LED painter. Though this is an SMD design, it uses the DIP package.
I like Digikey for SMD parts in small quantities. Many items I can also get locally here in Hong Kong or in the electronics market in Shenzhen. That isn't exactly an option for most people, but I bet that is what the company Duffer recommends is doing.
Nice idea about the microcontroller too. There are several low cost MCUs that would work in this situation. Deciding on the protocol is the hard part.
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Timothy D. Swieter, E.I.
www.brilldea.com·- Prop Blade, LED Painter, RGB LEDs, uOLED-IOC
www.sxmicro.com - a blog·exploring the SX micro
www.tdswieter.com