I have one sensor that goes on/off at times, I want to flash 2 LED strings (RED, GREEN) every 1 second using a 555 IC.

So when sensor ON 1st second GREEN-ON,RED-OFF 2nd second GREEN-OFF, RED-ON

the 555 IC can sink and source, do I use a P and N channel MOSFETs to drive the LEDS?

Is this schematic correct? have I connected the MOSFETS correctly and also I'm not sure about the 555 timing if it is 1 second ON 1 second OFF

enter image description here

Can anyone suggest different approach

Please help

  • 1
    \$\begingroup\$ How much current do you require for the red string and for the green string? What voltage are you using to operate the 555 in your schematic? And what voltage is required for each of your LED strings, as well? \$\endgroup\$
    – jonk
    Aug 11, 2016 at 18:12
  • \$\begingroup\$ about 2A for LEDs 12V, 555 is TTL voltage (I think) \$\endgroup\$
    – Seeker
    Aug 11, 2016 at 18:24
  • \$\begingroup\$ Okay. I wanted to be assured that the 555's output was itself inadequate given that it had an adequate supply of its own. The "TTL voltage (I think)" does need clarification, though. What is this connected to? \$\endgroup\$
    – jonk
    Aug 11, 2016 at 18:26
  • \$\begingroup\$ Ok, SENSOR is 5V (ill worry about that later if it is not) \$\endgroup\$
    – Seeker
    Aug 11, 2016 at 18:51
  • \$\begingroup\$ Can you use the +12V rail for the 555? Or does it have to be something much lower, like the +5V you mentioned? \$\endgroup\$
    – jonk
    Aug 11, 2016 at 19:02

1 Answer 1


You can drive the strings like this (555 circuit shown for 50% duty cycle when used with CMOS 555) M1 needs to be a logic-level MOSFET. For 1Hz (0.5s on 0.5s off, R6*C1 needs to be about 0.71, so you could use 1uF and 710K with a CMOS 555.


simulate this circuit – Schematic created using CircuitLab


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