# Circuit to delay sensor output

I have a digital IR-Sensor giving a low output while detecting something.

As I want to trigger something for a given time, I am looking for a circuit with an IC which can delay. As soon as the IR-Sensor pulls low, the IC shall output high for a certain time (around 1 second). Afterwards it shall pull low again. Then it shall stay low. If after the one second, the IR-sensor is still detecting something the delay IC should not output high, but wait until the IR-sensor stops detecting something:

Timing diagram for OP to edit.

         _____         _______   _______
Sensor        |_______|       |_|
_____           _____
Output   _____| 1 s |_________| 1 s |___


I am currently using an Arduino to do this job, but i was hoping to make the Arduino obsolete and to have a circuit doing the job. Any suggestions? Power consumption shall be low as possible. So maybe 555 timers if possible not. Thanks

• Some PIR sensors have fixed or adjustable "delay time" and "blocking time". Perhaps you might find them useful: fr.aliexpress.com/item/…. – tlfong01 Sep 16 at 14:06
• Google the terms "monostable" and "one-shot". Applies to 555 timer as well. – rdtsc Sep 16 at 14:07
• I've added a timing diagram for you. Please edit if it's not correct and make sure that it covers all your cases. (Mine shows that the output should stay on even if the trigger turns off.) Pay attention to capitalisation to make sure your post is clear and legible. – Transistor Sep 16 at 14:09
• I can make a delay with a resistor and a capacitor. When it's not active (steady state) it consumes zero power. Never ask for "as low as possible" because then I propose that I design for you a pico-current-555 which consumes almost zero power but it costs 1 million Euros to design and make. A 7555 is a low current 555 which you can have for a few euros and which will have a low enough current consumption (but feel free to prove that you need an even lower current consumption). – Bimpelrekkie Sep 16 at 14:12
• Alright, thanks. Having now a 555 or a 7555 as a monostable circuit, how do i add the functionality of the output staying low until the IR-Sensor pulls high again. – jacko91 Sep 16 at 14:44

A simple suggestion:

The same Arduino code that you are using now can run in a stand-alone microcontroller, instead of running in the microcontroller of the Arduino's board.

Perhaps it won't even be necessary to use a crystal, or other external components for the microcontroller.

The choice of the microcontroller is linked to the complexity and size of your code, and the number of pins of Arduino that you use now.

You can use the microcontroller ATMega328 (the same of Arduino Uno), or even, if your code is small enough, and the circuit use just a few of Arduino's pins, you can recompile your code and run it in a simpler microcontroller, like ATTiny85 (a small IC with just 8 pins).

• fair point. I am thinking about putting the application to a small series batch. So I wanted to check if it is possible to get rid of burning bootloaders and flashing to code on the atmega – jacko91 Sep 16 at 14:16
• Yes, if your code is small and you use just a few MCU pins, your best option is using a single small MCU and programming it directly, with no bootloaders. Just yesterday, I wrote an answer listing some ways of programming a microcontroller. The option 4 is very simple, doesn't requires a bootloader, and there are a lot of information about it in the internet. – mguima Sep 16 at 14:20
• I think this is a good suggestion. The micro-controller option allows you to change the delay easily without altering the physical circuit. You're also likely to encounter other unexpected behavior from a sensor which a micro-controller can mitigate. – David Sep 17 at 11:53