DIY LDR Switch Circuits

Here are some DIY LDR switch circuits available on our website and the web. LDR switches are used to switch a relay or other device when light are present or absent. LDRs or Light Dependent Resistors are very useful especially in light/dark sensor circuits.

Normally the resistance of an LDR is very high, sometimes as high as 1000 000 ohms, but when they are illuminated with light resistance drops dramatically.

LDR switch circuit diagrams

  • This is a light switch or light activated relay circuit. The relay on when LDR uncoverd and relay off when LDR covered. Adjust VR1 for light sensitive. LED will turn on at the same time with relay.
  • light activated relay circuit

  • This is the circuit diagram of a light activated switch based on National Semiconductors comparator IC LM 311 and a LDR.
  • light activated switch circuit diagram

  • The circuit below shows a simple application of ldr operated switch. This circuit senses the ambience light and depending on the presence/absense of sufficient ambience light, it turnes the bulb On/Off automatically. The bulb gets on when there is insufficient ambience light (e.g evening or night time) and switches off automatically when enough ambience light is present. (e.g In day time, when the sun light is present additional light may not be needed.) This bulb can also be your street lamp that needs to be switched on every evening, and switched off every morning. The circuit does this job automatically without any manual interference.
  • ldr operated switch

  • Light sensitive switch with LDR, actually it has a buzzer which will sound an alarm…
  • light sensitive switch with ldr

If you other LDR switch circuits related links, then please write about it on the comments section.

Comments are closed.