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Friday, October 18, 2019

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.

555 watchdog for uC and uP systems - delabs

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

Watchdog Timers can reset a microontroller or microprocessor system when it goes into an endless loop or gets stuck. 555 is used here to keep a tab on the uC activity. It resets when it senses the uC is not pinging it anymore.

Thursday, October 17, 2019

Fixed frequency Variable duty cycle with 555

This circuit is based on a very old application note from exar, in this the frequency is fixed by IC1 and IC2 -P1 controls the duty cycle. you need to compute the R and C values to get what you need,

Fixed frequency Variable duty cycle with 555 - delabs

You have to study the circuit and do something more innovative perhaps, just copying is ok for learning but it will get you nowhere, so learn and then innovate,

Fixed frequency var DC 555

You can even make a PCB at home to learn, but it is always good to get PCBs done by a PCB vendor, but you should understand his problems, then you will design well, so make a few PCBs.

Pulse width modulation using 555

IC1 astable gives a fixed square wave at pin 3, C1 and R1 derive uS trigger pulses from IC1 and this will trigger IC2 monostable or single shot, the voltage at pin 5 of IC2 will change the pulse width output of IC2, to get it working all the three RC combinations have to be figured out.

Optical Obstacle Switch.

Pulse width modulation using 555 - delabs circuits

You can even build a small SMPS with this or even control the temperature of your soldering iron using the SSR solid state relay circuits in power section, then you need to think and design the cycle time of a soldering iron heat control system, it will be in seconds but then above circuit is running at audio frequencies, then you have to work that out yourself..

Pulse width modulation using 555

The 555 was the first SmartChip of the early days, in those days we had Opamp and Logic Chips, this was a Mixed Signal Design chip that was Field Programmable, with presets of course. Innovation Par-Excellence.