I have design in Multisim with a 555 timer that I want to pull to ground when the signal changes. It's a missing pulse detector for resetting an mcu.

Is there anyway I can achieve this with say a transistor or mosfet?

I need it to pull to ground so i can reset a MCU.

enter image description here

  • \$\begingroup\$ What is your MCU ? Can't 0.7 V above ground reset your MCU ? \$\endgroup\$ – Long Pham Jul 17 '18 at 13:54
  • \$\begingroup\$ Arduino. I'm not sure. \$\endgroup\$ – Concerned Citizen Jul 17 '18 at 16:18
  • \$\begingroup\$ Look at this, voltage between 0 - 1.5 volt is considered logic low. \$\endgroup\$ – Long Pham Jul 18 '18 at 4:11

You can use CMOS version of IC 555 (LM555,.. for example). It will swing down to ground and up to VCC.

Or you can do this :


simulate this circuit – Schematic created using CircuitLab

Vcc depends on your MCU voltage and M1,M2 should be logic-level MOSFETs.

  • \$\begingroup\$ If i'm reading this correctly this will flip the output from the 555 and then pull it to ground, correct? Also, where can I learn about the cmos 555 pulling to GND when output is low? \$\endgroup\$ – Concerned Citizen Jul 17 '18 at 16:05
  • \$\begingroup\$ I found in second paragraph in the datasheet. intersil.com/content/dam/Intersil/documents/icm7/icm7555-56.pdf \$\endgroup\$ – Concerned Citizen Jul 17 '18 at 20:20
  • 1
    \$\begingroup\$ No, it doesn't flip the output. \$\endgroup\$ – Long Pham Jul 18 '18 at 4:06
  • \$\begingroup\$ ICM7555, they are a variant of CMOS 555. \$\endgroup\$ – Long Pham Jul 18 '18 at 4:07
  • \$\begingroup\$ I'm confused then, why use two MOSFETS then if it's not to flip the output? When gate on M2 is 'high" M1's gate will be pull to ground, and vice versa... I admit I'm still young to this but that's what I see here. \$\endgroup\$ – Concerned Citizen Jul 19 '18 at 11:16

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