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I'm looking into designing a badge for a tech conference and we're thinking of creating a small PCB with one or more LEDs on it.

Requirements:

  • Less than $5 per unit for 2500 badges
  • The PCB has to be around the size of a 3.5" floppy with place to add a sticker with the participant's name of it
  • A silk layer would be nice to show of the parts and complete the "geek" feeling
  • Ideally it would run on a "button"/"cell" battery, but a AAA battery might be needed.
  • It would be nice if it would run for up to a year, but the conference is two days so anything that would run for at least three days is doable

Options we're thinking of:

  • Blinking a single red LED
  • One "glowing" RGB led that changes between the three different colors of the event's design
  • A strip of RGB LEDs making the whole badge "glow"
  • Using some kind of plastic to use less LEDs to illuminate more of the badge

The question is: what kind of architectures should I look into?

The LM3909 is supposed to be nice, but out of production. Are there any replacement components like that?

For stuff that glows I see two possibilities some MCU (MSP430 perhaps?) to do PWM between one or three colors or use a D/A to set the voltage of the LED to an appropriate level.

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  • \$\begingroup\$ Sounds like a budget (read: boring) DEFCON badge. \$\endgroup\$ – Nick T Mar 4 '11 at 1:09
  • \$\begingroup\$ Hm, didn't know of those. I'll see if I can learn something from those. \$\endgroup\$ – Trygve Laugstøl Mar 4 '11 at 10:27
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The six-pin SOT-23 PIC10F200 is $0.32 for 1ku, and can use a supply down to 2V. That would be a good choice. If you need PWM it could be implemented in software, as the device includes a timer.

Another option would be the similar ATtiny4 from Atmel. It has more features, including PWM, but is more expensive at over $0.50 for 1ku.

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With some RFID components, you can do things like automated people tracking:

http://www.flickr.com/photos/blinkenarea/4800793412/

http://travisgoodspeed.blogspot.com/2010/06/hacking-next-hope-badge.html

I think thats a more interesting use of technology than yet another Blinking Bow Tie: enter image description here

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  • \$\begingroup\$ And you can sniff Microsoft wireless keyboards... travisgoodspeed.blogspot.com/2011/02/… \$\endgroup\$ – Toby Jaffey Mar 3 '11 at 16:16
  • \$\begingroup\$ We have used RFID cards for many years, and while fun they're more expensive. This year each visitor will get its own QR code which we'll scan on entrance and for participation in the different quizzes. \$\endgroup\$ – Trygve Laugstøl Mar 3 '11 at 20:05
  • \$\begingroup\$ Depending on the type of tech conference, you might get parts donated for PR value. That's how the Next HOPE badge was funded. \$\endgroup\$ – markrages Mar 3 '11 at 20:35
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The MSP430G2211 is under 50c in 1ku quantities. It could be a good fit. Here are a couple of my own flashing LED projects based on it.

RGB Lamp, LED Chaser

But, for a flashing LED, a 555 could be the obvious choice.

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  • \$\begingroup\$ How much do you think the total current draw would be for a PWM controlled RGB LED from a 1.5V battery? \$\endgroup\$ – Trygve Laugstøl Mar 3 '11 at 15:46
  • \$\begingroup\$ It would depend on the microcontroller and LED, you'd have to consult the datasheets \$\endgroup\$ – Toby Jaffey Mar 3 '11 at 15:53
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    \$\begingroup\$ You'd need to step up the voltage from a 1.5V battery. See Vf in the table: kpsec.freeuk.com/components/led.htm#data . 3V is a better choice. \$\endgroup\$ – markrages Mar 3 '11 at 16:17
  • \$\begingroup\$ A nice variation on binary code modulation, which I'm surprised I haven't often seen implemented in hardware, is to output the MSB on every other sample, the next bit on every other sample among those remaining, etc. This gives a cleaner steady-state signal than PWM, though updating the output value smoothly can be tricky. As with BCM, many bits can be handled in parallel. \$\endgroup\$ – supercat Mar 3 '11 at 18:05

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