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10

XY problem. This isn't a job for a 555. This needs to be dealt with by software, with a little help from RPi hardware. (Obi-wan voice: “Use the source, Luke…”) What hardware? The ARM architecture in RPi has a watchdog timer resource. The point of a watchdog timer is for the system get unstuck and recover. I encourage you to use it (see the link below.) ...


4

You could program another microcontroller, maybe an SOT23-6 or SOIC-8 package, to do that. It would be a simple program, running off an internal RC oscillator, and using an internal (reliable) BOR/POR peripheral. Just the chip and a bypass cap on the power supply. Alternately, you could use a resettable monostable multivibrator (not necessarily a 555) and a ...


3

Since you're using it for PWM the actual frequency is typically not all that important. The frequency will be about 1.4/(50K * 100nF). Because of the diodes the frequency will be lower at low Vdd. So in this case, about 280Hz. The capacitor charges through one portion of the 50K element and discharges through the other portion. Since 50K >> 1K, and pot ...


3

I want the status LED to blink when there's a fault instead of blinking to show there is not one. The following circuit may work for you, although I have not tested it. simulate this circuit – Schematic created using CircuitLab The 555 is configured as an astable relaxation oscillator. However, the timing capacitor can be shorted by Q1. If this ...


2

is there a name for such a circuit When you have your software pulsing something periodically to indicate that the software is running normally (not "locked up"), Watchdog: hardware that distinguishes between normal and locked-up software Feeding the watchdog: the bit of software that tells the watchdog that things are running normally. (Usually ...


1

In the standard monostable circuit, the 555 triggers on the negative-going edge. With Vcc = 9 V, the Trigger input has to sit above 3 V in the idle state, then go below 3 V to trigger the output. But ... The 555 is not a normal monostable. If the trigger input still is low when the circuit times out (in around 2 s in your case), the output will stay high ...


1

If you can substitute for the SPST switch you show in your drawing, a SPDT switch, with one contact connected to positive, and the other to negative, it will almost certainly make your solution simpler. Here is a possible solution for you. The timing of the circuit is not very accurate. If you need accuracy, let me know, and I will give you a more complex ...


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You are probably looking for a monostable circuit, which can either be accomplished with a 555 ic or with with a few transistors. Here is a small simulation using some bipolar devices. The trigger input was replaced with an inverter in order to latch on the positive edge (switch on).


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Configure one of the spare hardware timers to toggle an output based upon the counter value. For example, the timer counts up and rolls over at 0xFFFF and the output toggles at 0x7FFF and 0x0000 for a 50% duty cycle. After the software configures the timer at startup, then the toggling output will be under control of the hardware timer and doesn't require ...


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