I have a device built with an Arduino MKR WAN 1310 as it's main MCU. This Arduino will be in deep sleep mode most of time to save battery.
Now I need to implement an IR cut sensor (With an IR emitter and IR photodiode) and trigger an interrupt to the Arduino as soon as the IR beam is cut.
This way the arduino can stay in deep sleep mode while another circuit will wake it when needed.

To save battery I assume the best way to do this is buy putting the IR emitter on some kind of PWM turning it on/off at a specified interval. Checking for beam obstruction every 200ms is more than fast enough.
The receiver circuit should be counting the missed pulses to determine if the IR beam is cut or not and if it's cut: trigger an interrupt to the arduino.

Now I'm not sure what would be the simplest low-power circuit I can build for this purpose?
Any help / advice would be greatly appreciated.

The device will be running from batteries so it needs to be a low power circuit.

 

What is the distance between the IR receiver and transmitter?

 

Approximately 25cm. The IR emitter and receiver are already in place. It's in fact a modified device (custom PCB) that already had the emitter and receiver. I now need to reuse these in order to save power.

 

Most of the current will probably be in the IR emitter. Do you any part numbers for the emitter and receiver on that board? Is it a single piece unit?

 

I don't have any part numbers of the emitter/receiver. In worst case scenario I can replace them but I prefer to reused them. They are 5mm clear round IR emitter (2pins) and 5mm dark round IR photodiode (2pins)
But replacing them is possible.

For testing /measuring I reconnected the original PCB which was driving the IR emitters. I connected my oscilloscope to it and I can see pulses of 3.12v every 200ms. So I guess 3.12v is the maximum voltage to try.
I need to somehow measure the forward current of it, but it's never fully on. Always pulsing at 200ms. So might have to guess based on average forward current for a 5mm ir led.

But once again, replacing the IR led/receiver is an option too. Would love to hear a solution on how to make and IR beam cut sensor circuit that can be battery operated (low power) and trigger an interrupt to the mcu

 

Attached are pictures of the emitter/receiver.
There are 2 emitter and 2 receivers. They work independed but are on the same PCB, sharing GND.

 

What type battery and current capacity?

 

7.4v 6400mAh Li-Ion.
There's a LT1129 (low quencient power) to provide 5V to other parts of the circuit. The arduino also has another LDO voltage regulator providing 3.3V for sensors (if needed)

 

Either the 5 v or 3.3 will work.
Thinking a LMC555 to pulse the emitter and use an op amp or another 555 to process the receiver.

 

How would the op amp process the receiver? It somehow needs to 'count' the pulses and trigger an interrupt?

I don't think I'm experienced enough to build a circuit like that so an example would be very helpful, if possible.

 

How would the op amp process the receiver? It somehow needs to 'count' the pulses and trigger an interrupt?

Not necessarily. What is breaking the beam and for how long?

 

It depends. It can be 1-2 seconds or 3-4 minutes and anything in between is possible too ;-)

 

OK will go with 1 second minimum. First though is a 555 missing pulse detector with a delayed output under 1 second.
Can't draw anything up right now, heading into town for dinner.

 

I never used the 555 before but looking at the specs, it's indeed a low power device. So it seems like a good option but I will need some help with the circuit. Any chance you can come up with a circuit I can try with? I will happily order the 555 for testing.

 

Sure when I get back later tonight.

 

IR emitter transmit circuit.

 

Thanks. What is the pulse frequenct supposed to be with this circuit?

With a second 555 we should be able to build a circuit that will trigger an interrupt if a certain amount of pulses are missing. I found an example here: https://www.falstad.com/circuit/e-555missing.html

In total the circuits will be using 200uA not counting the Ir led’s power consumption.

ps: why is the bs170 needed for a led? The datasheet says it can output 100ma. The led won’tbe consuming more, I hope

 

https://forum.allaboutcircuits.com/threads/help-lowest-input-current-optocoupler.145712/post-1244122
Тhis circuit consumes 2.75 μA from 5 V source:

 

ps: why is the bs170 needed for a led? The datasheet says it can output 100ma. The led won’t be consuming more, I hope

Reduce the load on the 555. Without the mosfet the output voltage is only appx 2 volts.

 

IR transmitter and receiver. Receiver produces low output pulse after 1 second delay when the signal is blocked.
Verified at 25cm.

EDIT: Changed value of R3 to 220 ohms, reducing the current for the emitter. Still functional at 25cm. YMMV.