# Questions from a PLC newbie, for Opta

**URL:** <https://forum.arduino.cc/t/questions-from-a-plc-newbie-for-opta/1261419>\
**Category:** Opta\
**Created:** [May 18, 2024, 8:57am UTC](https://forum.arduino.cc/t/questions-from-a-plc-newbie-for-opta/1261419 "2024-05-18T08:57:45Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![FeliceMente](https://avatars.discourse-cdn.com/v4/letter/f/b2d939/32.png) [@FeliceMente](https://forum.arduino.cc/u/FeliceMente)\
**Post date:** [May 18, 2024, 8:57am UTC](https://forum.arduino.cc/t/questions-from-a-plc-newbie-for-opta/1261419/1 "2024-05-18T08:57:45Z")

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I'm experimenting with Opta (after buying the PLC Starter Kit).

1. As a PLC newbie, but with experience on Arduino and microcontrollers in general, I was surprised seeing how to connect a button input, directly, without any pull-down or pull-up resistors. Does the Opta have internal not configurable pull-down resistors or something similar?

2. I'm familiar with 5v and 3.3v power. Is operating with 24v safe, even if I touch the terminals?

3. What happens if I connect 24v input to an input of the Opta set as analog (that should accept 0-10v for analog signals)?

Thanks.

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**Author:** ![tlock0331](https://avatars.discourse-cdn.com/v4/letter/t/8491ac/32.png) [@tlock0331](https://forum.arduino.cc/u/tlock0331)\
**Post date:** [May 25, 2024, 12:42pm UTC](https://forum.arduino.cc/t/questions-from-a-plc-newbie-for-opta/1261419/2 "2024-05-25T12:42:45Z")

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24vdc has become the standard in industrial controls automation. That said, i wouldnt go out of my way to touch it, out of good habits, but it is safe, that is one of the reasons for switching from 120vac to 24vdc controls.

I doubt the Opta is internally protected, so its likely it would blow out that pin. just keep in mind that your analog devices can in a lot of dfferent styles, 0-5vdc, 0-10vdc, 4-20mA, 0-20mA, just to name a few. so if you have a mA transmitter you will need to either put in an external resistor to convert it to a voltage signal, or get a 5 dollar milliamp to voltage convertor board.

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**Author:** ![aubrey4485](https://avatars.discourse-cdn.com/v4/letter/a/e495f1/32.png) [@aubrey4485](https://forum.arduino.cc/u/aubrey4485)\
**Post date:** [May 26, 2024, 10:59am UTC](https://forum.arduino.cc/t/questions-from-a-plc-newbie-for-opta/1261419/3 "2024-05-26T10:59:43Z")

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> [@FeliceMente](#):
>
> What happens if I connect 24v input to an input of the Opta set as analog (that should accept 0-10v for analog signals)?

I would think being touted as industrial, if you have the input set to Analog and input a digital +24… the input should be fine…. However, i have no clue??

- You need to ask Arduino support in an email (not forum).
- If you have a lot of money, and can afford another OPTA, test this out yourself and play with it a little.

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**Author:** ![paolo\_marinelo](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/paolo_marinelo/32/1110001_2.png) [@paolo\_marinelo](https://forum.arduino.cc/u/paolo_marinelo)\
**Post date:** [November 7, 2024, 10:42am UTC](https://forum.arduino.cc/t/questions-from-a-plc-newbie-for-opta/1261419/4 "2024-11-07T10:42:41Z")

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Hello,  
Here's what I can do for you:

1. When you configure an input as Digital Input, the Opta internal circuit gives a low state when the voltage is below 4.46 VDC and a high state when the voltage is above 6.6 VDC. Between the two the state is unstable and cannot be guaranteed.
2. There is no risk of electric shock with a voltage of 24 VDC. It becomes dangerous above 48 VDC.
3. According to [this comment](https://forum.arduino.cc/t/dig-an-input-range/1112357/6) the only problem is that it saturates above 10V.