Electronics > Beginners
Timer alarm
darinsquared:
I am trying to devise a way to set up an alarm that is based on no motion. Basically the opposite of a motion sensor light. I know how to build this with a PIR sensor but I want the time before the alarm sounds longer than a typical PIR sensor allows. I want 4-5 minutes of no motion to trigger an alarm. I would think using a capacitor and 555 timer in some form.
Wimberleytech:
--- Quote from: darinsquared on November 30, 2019, 02:40:28 pm ---I am trying to devise a way to set up an alarm that is based on no motion. Basically the opposite of a motion sensor light. I know how to build this with a PIR sensor but I want the time before the alarm sounds longer than a typical PIR sensor allows. I want 4-5 minutes of no motion to trigger an alarm. I would think using a capacitor and 555 timer in some form.
--- End quote ---
Before digging into the specific implementation, is this the concept you are trying to achieve?
Every time the sensor detects motion, it resets the timer. Only when the sensor does not generate an output for 5 minutes, does the timer output to the buzzer. The buzzer needs to have its own timer so that when activated, it stays on for a desired length of time.
In terms of implementation, this is trivial with an arduino.
darinsquared:
--- Quote from: Wimberleytech on November 30, 2019, 03:43:01 pm ---
Before digging into the specific implementation, is this the concept you are trying to achieve?
Every time the sensor detects motion, it resets the timer. Only when the sensor does not generate an output for 5 minutes, does the timer output to the buzzer. The buzzer needs to have its own timer so that when activated, it stays on for a desired length of time.
In terms of implementation, this is trivial with an arduino.
--- End quote ---
Basically correct. I have aging parents and I want to set an alarm in the kitchen so that when they are cooking they can physically start the alarm when they are cooking. When they leave the kitchen and no motion is detected for 5+ minutes an alarm will sound to remind them some thing is on the stove.
I prefer straight electronics over Arduino. Ideally there would be a relay on the power supply to the stove that would cut out when there is no motion for extended period.
jhpadjustable:
It's also nearly trivial with a 555. You need only provide your own transistor for retriggering. Bringing the "H" input low brings the output high and resets the timer. You'll also need to bring your own inverter if your PIR module output goes high when presence is detected.
Wimberleytech:
--- Quote from: darinsquared on November 30, 2019, 04:10:07 pm ---
--- Quote from: Wimberleytech on November 30, 2019, 03:43:01 pm ---
Before digging into the specific implementation, is this the concept you are trying to achieve?
Every time the sensor detects motion, it resets the timer. Only when the sensor does not generate an output for 5 minutes, does the timer output to the buzzer. The buzzer needs to have its own timer so that when activated, it stays on for a desired length of time.
In terms of implementation, this is trivial with an arduino.
--- End quote ---
Basically correct. I have aging parents and I want to set an alarm in the kitchen so that when they are cooking they can physically start the alarm when they are cooking. When they leave the kitchen and no motion is detected for 5+ minutes an alarm will sound to remind them some thing is on the stove.
I prefer straight electronics over Arduino. Ideally there would be a relay on the power supply to the stove that would cut out when there is no motion for extended period.
--- End quote ---
LOL, this is a very good idea. I am an aging parent (Grrr!!!!!) and more than a few times I have left something cooking on the stove. Right now, I have a timer next to the burners...when I start something, I set the timer to warn me. It works, but I like your idea as well. jhpadjustable posted a simple solution. Cascade with another 555 to keep the timer running long enough for your parents to hear it.
You are a fine son!
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