0
\$\begingroup\$

I have installation with Controllino mini, it's essentially an ATmega328, and with 6 LDRs and 6 lasers, creating laser rays/barriers.

The system acts as a lasers labyrinth for entertainment purposes, and it's working for approximately a year. One of the LDR's - just generic one you can buy in every electronics component shop, stopped working as it should. Meaning - it outputs constant voltage no matter what are the light conditions. The installation of the sensor consists of +12V input on one pole, and connection to the ATmega328 based PLC analog input on the another pole with a 10K resistor to GND.

schematic

simulate this circuit – Schematic created using CircuitLab

After taking it apart, the measured resistance on the LDR was constant (don't remember the exact value) and not reacting to different light conditions. I did replace this sensor, but after a week or so, the same problem occurred again.

This, and the fact that it was working for a year without issues, made me believe there might be external factor affecting it/ taking it out of order.

Why did the LDR or circuit fail after a long period of time?

\$\endgroup\$
2
  • \$\begingroup\$ I'm not sure LDRs were ever really mean to be blasted with lasers... \$\endgroup\$
    – Trevor_G
    Apr 24, 2017 at 18:19
  • \$\begingroup\$ Its a 5v@25ma red dot 650 nM Laser. All sensors/LDRs are working for more then a year, without issues. Only this one stopped working normally after 12 months of operation. \$\endgroup\$
    – Eli
    Apr 25, 2017 at 18:11

1 Answer 1

3
\$\begingroup\$

Don't know if this is the cause of LDR failure, but your circuit has a basic flaw: A +12v supply can cause damage to the ATmega328, when the photo-resistor's resistance is low enough to raise the Analog input pin above ATmega328's Vdd (+5v?). Too much current can flow.
The solution is to lower the +12v supply to no more than ATmega328's Vdd voltage. You may have to lower the threshold where you decide if the laser beam has been blocked, because with a lower supply, your circuit will be less sensitive.

\$\endgroup\$
2
  • \$\begingroup\$ Hi Glen thanks for answering. Its an Atmega based PLC. Ive attached link above. Normal operating voltages for its IOs are 12/24V. \$\endgroup\$
    – Eli
    Apr 25, 2017 at 18:13
  • \$\begingroup\$ @Eli It would appear that the PLC analog input conditioning makes your circuit OK. I can only suggest that Trevor's suggestion of concentrated laser power might cause spot overheating. A de-focused beam might help. \$\endgroup\$
    – glen_geek
    Apr 25, 2017 at 18:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.