Hello,

First, i hope i'm posting this in the right forum. If not, Please let me know where to move it to.

I'm trying to replace a sensor that is prone to malfunction quite easily and give false positive/false negative. The way i'm doing it is connect the sensor to an arduino along with a load cell to figure out if indeed the IR made the right call. So there will be 2 point of failure instead of one.
The way im planning to do so is to connect the output of the IR sensor to a voltage divider so it will be able to trigger the arduino interrupt.


My problem is as follows:

1. The IR sensor operates at 12V. During idle he outputs 0V and around 20mA. While he is on, he output 12V with 0mA.
Another issue is that i don't have the schematics of the circuit it goes into, so i can't try to understand the works behind it. I'm trying to understand the PCB itself but it is also quite hard.
The problem is, i have never met such a behavior so i can't under stand how to imitate the sensor behavior.
2. Once i connect to output of the sensor to the voltage divider the voltage drops to ~1V... that seems strange to me. i thought to connect the sensor output to an N-MOSFET in order to make the connection to the arduino.

Does this behavior sounds familiar? Can you please point me to a direction of operation?
I would love to hear your ideas and suggestions.

Thanks a lot.

 

Post datasheet or link for sensor.

Regards, Dana.

 

Hi,

I don't have a data sheet for the sensor (other wise it would be a lot easier...)
Its a complete PCB assembly for the sensor. Here is an example (sorry i didn't attached it before)
https://www.aliexpress.com/item/Cra...c6-4653-b3b5-4015b842a4d3&transAbTest=ae803_4

 

Have you considered whether it might be a current loop controller? Tons of reading but here are two links:

https://en.wikipedia.org/wiki/Current_loop (history)
https://www.predig.com/indicatorpage/back-basics-fundamentals-4-20-ma-current-loops

 

Have you considered whether it might be a current loop controller? Tons of reading but here are two links:

Thanks for the links! I'll read them.
I'm not familiar with current loop, as i have never worked with the industrial stuff.

If you have any recommendation about how to "imitate" this behavior i would love to learn.
The links don't quite tell it...
Do i need to add a controller of some sort that an arduino will control? Or is there another way with passive parts?

Thanks

 

By the way - i saw a few tutorials on the current loop and they say the current stay constant at all times even if the voltages is changing. So that is not the behavior i saw...
Could it be something else?

 

Yes, it could be something else. We don't know anything about your sensor. I mentioned current loop signals only because you were perplexed by the voltages you saw. There are other types of signals too, such as PMW that can give seemingly odd voltages when measured with a voltmeter, but make great sense if viewed with an oscilloscope.

Can you provide a link to the sensor you are using?

 

You can’t

Yes, it could be something else. We don't know anything about your sensor. I mentioned current loop signals only because you were perplexed by the voltages you saw. There are other types of signals too, such as PMW that can give seemingly odd voltages when measured with a voltmeter, but make great sense if viewed with an oscilloscope.

Can you provide a link to the sensor you are using?

See post #3, @jpanhalt

 

I saw that post originally, and my immediate thought was caveat emptor.

I have extremely limited experience with Aliexpress (once). Information on the site is usually quite limited. However, I was lucky, and after a verified purchase, the vendor responded with a full datasheet. Some vendors prefer not to provide information until a purchase is verified. The competition is stiff, and I assume that practice is to prevent giving anything away to potential buyers who might buy from someone else. I even have seen comments to the effect of, "Once you buy, we will send instructions."

"Not available" is strongly influenced by how hard one had tried to get it .

 

@jpanhalt thanks for the detailed reply.

It's not PWM, i have viewed it with a scope and it gives only 2 signals of HIGH-LOW-HIGH- LOW.
What i'm thinking of, is to imitate the 12V 0mA but i don't know how... I would appreciate any suggestion on how to do so...

I think the 0 current comes from high impedance in the PCB but i cant know for sure, since to be able to track the trace on the PCB i'll have to un-solder most the components.
What i did tried is to imitate it by using a relay to switch the 12V line, but that only made damage, so i'm reluctant to try it again.
I will try to get the data sheet for the sensor.

 

Perhaps it would be best to start at the beginning.

What are you trying to do, and why did you think a "coin pusher" controller would help? Can you post diagrams of your original idea and how you got the measurements of voltage and current, including where the milliamp meter and oscilloscope were connected?

What is your signal to the "IR" sensor? I am presuming it is like a break-beam gate that counts the coins as they are inserted or dispensed, which would be consistent with the on/off characteristics you are seeing. However, such sensors are extremely common, simple, and a lot less expensive than the device you bought. Which raises the question, what about the particular device you bought attracted you to it?