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jotaro , 05-07-2026, 05:40 PM

I am looking for a cheap andn low range solution to detect presence interrupt a microcontroller to wake it from sleep mode and my research led me to this part, which is a reflective infrared emitter/collector sensor. However, I see it sold as a breakout and a single piece itself, refer to the images

I think the single piece itself should be able to detect and output a signal even without all those extra parts present on the breakout board right? I am not sure where to look to confirm this 100%

, 05-07-2026, 05:43 PM

🤖 In the meantime, here’s a response from the [FEDEVEL AI HW Assistant]().
It helps to find relevant resources for your question, but it may make mistakes as it’s still in early development.

This is the response from the AI Assistant:
The TCRT5000 infrared sensor can be used as a standalone component, but you'll need to add external circuitry to make it functional for microcontroller wake-up applications. Here's the breakdown:

1. **Core Functionality**
The TCRT5000 itself contains only the IR emitter and phototransistor - it needs external resistors to operate:
- Current-limiting resistor for the IR LED (typically 100-200Ω)
- Pull-up resistor for the phototransistor output (value depends on your detection range needs)

2. **Breakout Board Advantages**
Pre-made breakouts typically include:
- Optimized resistor network
- Comparator circuit for clean digital output
- Power filtering capacitors
- Status LED indicators

3. **Wake-Up Implementation**
For sleep mode applications:
- The raw sensor output is analog (varies with reflection distance)
- You'll need either:
- A comparator circuit (like on breakouts) to create digital interrupt
- Microcontroller ADC with threshold detection in firmware

4. **Design Tradeoffs**
- **Standalone**: Cheaper but requires PCB space for support components
- **Breakout**: More expensive but plug-and-play with digital output

Example from similar designs:
A battery management module used standalone sensors but required external pull-ups and filtering ([Source](https://www.youtube.com/watch?v=dHi4b9t5NYw&t=2030)). Breakout boards simplify this by integrating support components.

Recommendation:
If you're space-constrained or need reliable digital triggering, use the breakout. For lowest cost and have PCB space, use the standalone with 2 resistors and a comparator (if needed).

, 05-07-2026, 05:43 PM

Always verify with the sensor's datasheet for specific resistor values.

You can continue chatting with the AI Assistant here:
https://fedevel.com/hw-assistant

QDrives , 05-07-2026, 09:26 PM

The part is "analog". An interrupt is digital.
You need to make the conversion.

jotaro , 05-07-2026, 11:22 PM

what would I need to convert the AC to DC if not using the breakout

Robert Feranec , 05-08-2026, 06:58 AM

this looks like the schematic: https://easyelecmodule.com/tcrt5000-infrared-reflective-sensor-how-it-works-and-example-circuit-and-code-based-on-arduino/

Robert Feranec , 05-08-2026, 06:58 AM

jotaro , 05-08-2026, 10:01 AM

i only understand that the blue led that emits the IR has a current limiting 180 ohm and the collector led has 10k pullup

but i dont know what that op amp does or its inputs like that "VR1" thing
i think the op amp is acting as a rectifier? how does that work

QDrives , 05-08-2026, 11:23 AM

Did you read the text in the link provided by Robert?
The schematic has a comparator, not op-amp. Same symbol, but (slightly) different function.
A comparator is turning an analog signal (compared to a reference -- VR1) into a digital signal.

AC = Alternating Current
DC = Direct Current
That is not "Analog" and "Digital"

jotaro , 05-08-2026, 11:33 AM

it mentioned op amp here

jotaro , 05-08-2026, 11:34 AM

so that 10k resisotr at vr1 is a pull down right, does the comparator work by comparing the voltage at the phototransistor relative to the ground and output a fixed DC signal?

QDrives , 05-08-2026, 02:58 PM

The LM393 is a comparator, not an op-amp. It also states that.
https://www.electronics-tutorials.ws/opamp/op-amp-comparator.html

VR1 does not have a pull-down, nor pull-up. Is is between Vcc and Gnd. A 10kΩ trimpot.

jotaro , 05-08-2026, 02:59 PM

oh so that's what VR is

jotaro , 05-08-2026, 02:59 PM

variable resistor = trimpot

QDrives , 05-08-2026, 03:01 PM

Trimming potentiometer or trimpot.
https://www.digikey.nl/en/products/filter/trimmer-potentiometers/80

jotaro , 05-08-2026, 03:01 PM

isnt a comparator a type of op amp

jotaro , 05-08-2026, 03:01 PM

that is what I am understanding from the wording

jotaro , 05-08-2026, 03:01 PM

op amp is general

QDrives , 05-08-2026, 03:02 PM

You can make a comparator from an op-amp (limits apply).

jotaro , 05-08-2026, 03:03 PM

so what does that variable resistor do mathematically with that comparator

jotaro , 05-08-2026, 03:03 PM

the wiring is confusing me what is this resistor here for after the comparator

jotaro , 05-08-2026, 03:04 PM

i think it is a pull up?

jotaro , 05-08-2026, 03:04 PM

i assume every piece here is connected to vcc

QDrives , 05-08-2026, 03:05 PM

The LM393 has an open collector output. Hence you need a pull-up.

QDrives , 05-08-2026, 03:05 PM

Yes. All dots.

jotaro , 05-08-2026, 03:08 PM

after some chatgpt, that VR trimpot seems to be the adjustment for the "hysteresis" of the amp

jotaro , 05-08-2026, 03:09 PM

this the formula

jotaro , 05-08-2026, 03:09 PM

r1 must be 10k at the non inverting and r2 must be the trimpot

QDrives , 05-08-2026, 03:10 PM

Not hysteresis, but the 'setpoint'.
There is no hysteresis in this design.

jotaro , 05-08-2026, 03:12 PM

is there no feedback

jotaro , 05-08-2026, 03:12 PM

thats what the trimpot is for isnt it

QDrives , 05-08-2026, 03:12 PM

Not realy.
Here it is much simpler: just compare two voltages. The one given by the TCRT5000 and the one set by the trimpot.

QDrives , 05-08-2026, 03:13 PM

No feedback. Rarely used with a comparator.

jotaro , 05-08-2026, 03:14 PM

wait let me draw

jotaro , 05-08-2026, 03:16 PM

jotaro , 05-08-2026, 03:16 PM

is this what the op amp circuit looks like

jotaro , 05-08-2026, 03:17 PM

what do the resistors at the + and - do

jotaro , 05-08-2026, 03:18 PM

well i forgot to draw gnd for the - side

jotaro , 05-08-2026, 03:18 PM

but it should be there

jotaro , 05-08-2026, 03:19 PM

or i could be misunderstanding

QDrives , 05-08-2026, 03:35 PM

Yes, you are misunderstanding.
Learn more about comparators, potentiometers and transistors.
Or buy the breakout board and play with it.

jotaro , 05-08-2026, 06:41 PM

jotaro , 05-08-2026, 06:42 PM

the op amp compares the voltage entering into + with the voltage at -
and the variable resistor/potentiometer is basically a voltage divider internally right so it will allow me to adjust the voltage entering -

the op amp will output vcc on the right side when + is more than -

jotaro , 05-08-2026, 06:42 PM

did i get this right

QDrives , 05-09-2026, 05:12 PM

A "comparator" compares.
An op-amp amplifies the difference. With feedback you control how much the amplification is. Remove that feedback, and it will drive either - or +. In a sense creating a comparator.

For the rest your text is correct.

jotaro , 05-11-2026, 09:19 PM

what is the resistor at + side for? can it just connect to vcc without?

QDrives , 05-11-2026, 11:23 PM

"*can it just connect to vcc without?*" - if you want a smoke machine.
The sensor controls current. A comparator needs voltage.