Switching external Machine

Hello guys,

I am really sorry to annoy you with this probably easy problem, but I just can't figure it out.

So I got a machine who by now has a manual switch triggered by hand to do some action. The switch is connected to a Digital Input Module which does everything further and controlling the machine. Simplified, the manual switch would be the like this: |500x212

The switch is going to be automated by using an arduino and it would be triggered with a rather low frequency of about 1-2 Hz. I don't know anything else about the machines Digital Input Module, only that the current will be 200mA max.

I thought about getting the IRF520 board (I know about the "problem" with the gate voltage) and so to speak replace the manual switch with a MOSFET. My suggestion would be this: |500x331

However I am not sure if this would work, usually I saw MOSFETs switching GND and not the whole voltage, and I don't know where my "load" is, which typically also would be placed "above" the drain of the MOSFET.

Any help would be very appreciated, even if it's just "better use a relay". Thank you! :)

Suggest using an opto fet

https://www.mouser.com/datasheet/2/149/H11F3M-189245.pdf

Edit 200mA looks too much :(

Thanks for your reply, larryd!

The 200mA is a maximum value, the expected current will be around 10mA.

I will look into using opto fet. In a fit of curiosity, why wouldn't you recommend using a transistor?

EDIT: One of the few boards I found is this one: https://www.sparkfun.com/products/9118 It's not using the Opto FET you linked, but I can't really see a difference between those.

After some additional research, I figured that using an Optocoupler is my best choice and it shouldn't be too hard. However, there were some wiring diagrams which used some more MOSFETs or pull-ups on the output-side, do I need them? Will this work with 24V?

I_F was given as 60mA max in the H11F1M Datasheet, given other diagrams I choose a typical I_F of 5mA and a resistor of 650 Ohms.

|500x220

That might work, but I would lower R1 to about 220 Ohms.

The breakdown voltage of the H11F1 is 30V, which is a bit too close to 24V for comfort. I would choose a different optocoupler. I see no reason to use a FET optocoupler, and the H11F1 in particular is not intended to be used as a switch.

Its best to post details of the machine - rather than report second hand about it.

I don't know anything else about the machines Digital Input Module, only that the current will be 200mA max.

Is rather vague - and certainly isn't guaranteed to work with any opto coupler.

jremington: That might work, but I would lower R1 to about 220 Ohms.

The breakdown voltage of the H11F1 is 30V, which is a bit too close to 24V for comfort. I would choose a different optocoupler. I see no reason to use a FET optocoupler, and the H11F1 in particular is not intended to be used as a switch.

Hey jremington, thank you! I looked into using SFH617A. It got a much bigger V_CE with 70V and in the data sheet it says it's good for switching operations. Would that be a better choice?

MarkT: Its best to post details of the machine - rather than report second hand about it.Is rather vague - and certainly isn't guaranteed to work with any opto coupler.

Unfortunately I got no datasheet available. I thought this was a rather easy task, that I was just to silly for, but I'll look if I can find more. A HIGH of the DI Module is defined as 15V (min 3.7mA) or more at the input, a LOW 5V or less. Maximum Current is rated 200mA.

A HIGH of the DI Module is defined as 15V (min 3.7mA) or more at the input, a LOW 5V or less. Maximum Current is rated 200mA.

These specifications aren't entirely clear. Can you post a link to where you found them, or a photo of that page in the user manual?

The SFH617A is a better choice. Try it using the circuit posted in reply #3. You may need a pulldown resistor from the machine's input to ground (try 10K).