555 watchdog for uC and uP systems

When the microcontroller hangs due to a spike, EMI or RFI etc. the 7555 will reset the uC, if proper power supply design is done above circuit can also give a clean power on reset, the above circuit you should modify to suit your design.

80C39-8749 MCS-48 Examples and code

Better still use a uC with watchdog built in like some atmel chips, or use the watchdog chips from maxim which can also do RAM battery management.

The circuit was developed over a old TI application note, 7555 i think fairchild may be making it, 7555 is CMOS version of 555 timer, advantage of 7555 is that it can go to higher frequency, low power consumption, the disadvantage is its output drive mA is not as good as 555. now why i put it here was that you can see how charge and discharge paths are separated with diodes.

555 watchdog for uC and uP systems

See Larger Circuit. 555 Watchdog
Edit the circuit eagle cad file del00013.zip,

  • Musical Sound to Neon Light Flasher
    Neon Light Flasher was made by me when i was young, it was even published in a magazine, i think it will work, it was [...]
  • Tera Ohm Meter and Insulation Tester
    This is a 20 Tera Ohm Insulation Tester I made around 20 Years Back. It had even Polarization Index for Transformer Insulation. It generated 1000V [...]
  • Buffer or Unity Gain Op-Amp
    If output impedance of a point is a high value then connecting another circuit at that point will load it resulting in malfunction or error. [...]
  • Resistance Measurement Analog LED Meter
    This is a LED Analog Meter, This can be used as a Resistance Meter and Low Impedance Voltmeter for Battery Levels. To measure battery voltage, [...]
  • High Resistance Meter
    I don’t remember if this circuit worked properly. But a few were made and i might not have shown the modifications that were done to [...]
  • Running Lights with CD4017
    The 555 Astable generates a clock for this circuit, an oscillator giving a square wave output at pin 3 which is counted by 4017 to [...]
  • Non-Inverting Amplifier – Op-Amp CircuitsNon-Inverting Amplifier – Op-Amp Circuits
    The input impedance of this module is very high, if U1 is OP07 it is in mega ohms, use CA3140 or LF356 fet input opamps [...]
  • Stabilizer Step up 110V AC to 230V AC 500VAStabilizer Step up 110V AC to 230V AC 500VA
    It can Stabilize Mains voltage to around +/- 10% . It can be used for both 110V AC or 220V AC inputs with modifications. The [...]
About delabs 160 Articles
Product Design - Industrial Automation and Instrumentation. -