Reducing IR proximity sensor module power consumption

Question

I have built a rechargeable automatic hand sanitiser using an IR proximity sensor(HW 201.) It consists of an IR proximity sensor module, TIP 32 transistor, 3-6 V DC pump, TP4056 charging module and a 3.7 V Li-Ion 3800 mAh rechargeable battery.

I'm facing an issue with power consumption.

The battery drains too fast - it is empty after 1 or 2 days.

The IR sensor consumes about 20mA even during idle state (when not sensing hand.)

Is there any option to reduce the power consumption using 555 timer IC or any other programmable MCU (no Arduino?)

How can I make a low power consuming IR proximity sensor circuit?

Answer 1

1. Remove the two LEDs (over by the connector in your picture.) Lighting them uses current. Not much, but you don't really need them.
2. Increase the resistor in series with the IR emitter LED.

(2.) will probably have the most effect. It will probably also reduce the detection range.

Use a camera to find out which of the two LED like things is the IR emitter (on the right end of your picture.)

I expect it will be the clear one.

In any case, you can "see" IR with most digital cameras (smartphone cameras, photo cameras, webcams, etc.) Look at your sensor through the viewfinder of your camera and see which is lit up.

Trace the connections to that part. You will find a resistor in series with it.

I expect that resistor will be some few hundred ohms.

Replace it with a larger value resistor. A value of two or three times the original should be a good starting place.

Try your sensor out. If it works reliably, run it for a couple of days and see how your battery holds up.

Try a larger value to get a longer run time, but keep in mind that a larger resistor will shorten the detection distance and at somd point the detector will not work anymore.

Answer 2

If you use a discrete bipolar with 1uA collector current, set by 4.7Meg Ohm resistor to +5v, and Cob of the transistor is 10pF (for example), you'll have a time constant of 47 microseconds.

A 200 microsecond IR pulse should be adequate for detection.

Answer 3

I'm wondering why a 20mA current draw would drain 3800mA battery in 2 days. Simple mathematics indicate a good week of standby time with the module always on.

It's very likely that the battery itself is cheap/beated, being not able to provide the capacity it's rated for.

Or, maybe the pump draws too much power. Calculate the consumption of the motor by it's on-time duration and times it's activated within a charge cycle.

Removing indication LEDs, decreasing the range, and reducing on-time will do expand the battery life, though you'd better find out what is wrong there first.

Answer 4

I see two options here

Option 1 - You could spend some more money and get a purpose built PIR module with ultra low power consumption. Panasonic have a range for this purpose, one of the lowest power versions is the EKMB1107113 with 1.9 uA current draw. These are not cheap though and cost around £20 in the UK. With one of these you could put your MCU in deep sleep while no PIR motion is detected & wake up on PIR motion, this would maximise your power usage.

Option 2 - I think what you are trying to say is to modulate the on time of the IR modules to reduce its power consumption. You claim 20mA at 100% on time. If you use a Timer to reduce the on time to 100ms you could effectively multiple your battery drain time by 10.

You could have the power rail of the IR module connected via a Transistor with its gate toggled by a 555 timer with a 1:10 ratio setup and this could improve your performance.

Possible 555 Solution

I would strongly recommend you looking into how 555 timers work and transistor theory. Electronic Tutorials has some great explanations,

https://www.electronics-tutorials.ws/waveforms/555_timer.html

https://www.electronics-tutorials.ws/transistor/tran_2.html

The easiest solution I can imagine can be seen in my LTSpice simulation below,

You can adjust R1, R2 & C2 to vary the time characteristics of the NE555 Output Pulse, you can then use this output pulse signal to control an NPN transistor that is toggling the IR Modules power supply.

The simulation above is just a suggestion for how you could solve this problem, you would need to dial in the specific values to ensure that the IR module is getting enough power and the duty cycle is what you want.