I'd like to build a batteryless circuit to blink an led. I would like a solar cell to charge a capacitor until there is enough power to flash the led. The led flashes and the cap goes back to charging. This way the led will blink faster or slower depending on the light intensity.

From what I've read it seems a neon bulb might be required ?

Would this work ? The simulator charges the cap but the cap won't discharge through the led. Circuit Image

  • \$\begingroup\$ no, you don't need a neon bulb. you need a 2nd voltage ref or a transconductance amplifier. you can then use a 555, an opamp, or a basic blinker circuit. \$\endgroup\$
    – dandavis
    Commented Jun 2, 2017 at 20:02
  • \$\begingroup\$ Sure fire an scr with a zener diode \$\endgroup\$
    – sstobbe
    Commented Jun 2, 2017 at 21:48
  • \$\begingroup\$ I'm trying to use an SCR with a zener diode, but none of the simulators seems have the capacitor "dump" out to the led, it just stays at the charged voltage. \$\endgroup\$
    – tavis
    Commented Oct 4, 2018 at 8:31

1 Answer 1


A Programmable Unijunction or PUT is simplest with RC1 to trigger the gate from a charged RC cap for the Anode and dump the charge into an LED thus charging up in a sawtooth. http://www.onsemi.com/pub_link/Collateral/2N6027-D.PDF

  • \$\begingroup\$ Thanks for this idea. I just wish there was a way to do it with more basic components. \$\endgroup\$
    – tavis
    Commented Jun 4, 2017 at 20:58
  • \$\begingroup\$ A unijunction is the most basic semiconductor after a diode it doesn't get any simpler to realize . It's a negative resistance switch with a threshold voltage \$\endgroup\$ Commented Jun 5, 2017 at 2:10

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