LED-LDR Ring Oscillator

Published in issue 7/2012 on page 28

Can high-brightness white LEDs and light-dependent resistors (LDRs) be used to make an oscillator? I decided to have a go. For the experiment I chose type PGM5516 LDRs which have a relatively low resistance (5 kOhm to 10 kOhm at 10 lux). A ring oscillator configuration was used, with each LED placed directly next to its neighbouring LDR.

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