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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.

Trygve Laugstøl
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3 Answers3

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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.

Leon Heller
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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.

Toby Jaffey
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  • How much do you think the total current draw would be for a PWM controlled RGB LED from a 1.5V battery? – Trygve Laugstøl Mar 03 '11 at 15:46
  • It would depend on the microcontroller and LED, you'd have to consult the datasheets – Toby Jaffey Mar 03 '11 at 15:53
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    You'd need to step up the voltage from a 1.5V battery. See Vf in the table: http://www.kpsec.freeuk.com/components/led.htm#data . 3V is a better choice. – markrages Mar 03 '11 at 16:17
  • 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. – supercat Mar 03 '11 at 18:05
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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

markrages
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  • And you can sniff Microsoft wireless keyboards... http://travisgoodspeed.blogspot.com/2011/02/promiscuity-is-nrf24l01s-duty.html – Toby Jaffey Mar 03 '11 at 16:16
  • 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](http://en.wikipedia.org/wiki/QR_Code) which we'll scan on entrance and for participation in the different quizzes. – Trygve Laugstøl Mar 03 '11 at 20:05
  • Depending on the type of tech conference, you might get parts donated for PR value. That's how the Next HOPE badge was funded. – markrages Mar 03 '11 at 20:35