I found a circuit that has an led that is blinking in it. I was interested to see how it works so I took it apart and found that there was no capacitors in IC's in it (here is a picture):enter image description here

I think the thing under the white circle is a spark gap, but I'm not positive. My question is how does this LED blink without any capacitors?

  • 2
    \$\begingroup\$ You can get LEDs that flash without external circuits. As an example: digikey.com/product-detail/en/lumex-opto-components-inc/… \$\endgroup\$
    – b degnan
    Mar 14 '17 at 19:02
  • \$\begingroup\$ it could be anything under then... even a small microcomputer... Since I don't have x-ray vision... It's pretty hard to say. \$\endgroup\$
    – Trevor_G
    Mar 14 '17 at 19:05
  • \$\begingroup\$ @Trevor I took this picture of the other side of the board and you can kind of see what's under it : imgur.com/a/p8Wm9 Does this help determine how the circuit works? \$\endgroup\$
    – Tyler
    Mar 17 '17 at 19:33
  • \$\begingroup\$ Not really, its a 4 pin device, or at least it has four pads.. but that means nothing. \$\endgroup\$
    – Trevor_G
    Mar 17 '17 at 19:38

There are two possibilities:

  1. The LED is really an integrated unit that contains the flashing logic. Such things exist. You apply power, and it flashes.

  2. There is an IC under the white blob. This is a high volume but low cost production technique called chip on board or "COB".

I think #2 is more likely, especially considering the mass-produced high-volume look of this device. LEDs with integrated flashers are relatively rare and therefore expensive. A dumb flashing chip, especially without package, can probably be had for a few pennies in high volume.

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    \$\begingroup\$ I'd add that circle bottom right looks like it is meant for a push on push off function too.. which makes the chip almost a certainty. \$\endgroup\$
    – Trevor_G
    Mar 14 '17 at 19:09
  • \$\begingroup\$ I took a picture of the other side and you can kind of see what is underneath the blob: imgur.com/a/p8Wm9 Does this help determine how it works? \$\endgroup\$
    – Tyler
    Mar 17 '17 at 19:32

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