<p>I have a Tevo Tornado Gold 24&nbsp;V. I want to use this LJ12 A3-4-Z/BX Inductive NPN NO 4&nbsp;mm with 6-36&nbsp;V operation current as a Z probe. I do not want to fry my machine by putting in 24&nbsp;V into the sensor input.</p>

<p>What do I have is a 12&nbsp;V, single channel optocoupler isolation module.</p>

<p>I want to know if this 12&nbsp;V optocoupler module can be used with a 24&nbsp;V power supply, or do I need another module in order to prevent me frying my sensor.</p>

<p>If I do need another what would I need?
<a href="https://i.stack.imgur.com/cxoYG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cxoYG.png" alt="enter image description here"></a></p>

[{'answer_id': 10794, 'author': 'Trish', 'author_id': 8884, 'author_profile': 'https://3dprinting.stackexchange.com/users/8884', 'pm_score': 0, 'selected': False, 'text': '<h2>Not using a 12\xa0V rated module <em>&quot;on its own&quot;</em>.</h2>\n<p>Using a 12\xa0V/5\xa0V optocoupler to try to connect 24\xa0V to the 5\xa0V circuit is running the optocoupler outside of its rating, meaning you will destroy it, either immediately or after a short time.</p>\n<h2>A properly rated one</h2>\n<p>To shield the 5\xa0V against the maximal 24\xa0V from the probe without extra parts, you will need to use a 24\xa0V/5\xa0V optocoupler.</p>\n<h3>Trickery with voltage dividers</h3>\n<p>With a 50\xa0% <a href="https://en.wikipedia.org/wiki/Voltage_divider" rel="nofollow noreferrer">voltage divider</a> made from two properly rated resistors, you could limit the voltage to the optocoupler, which in turn would turn the 24\xa0V signal into a 12\xa0V signal, which would protect our optocoupler and the board beyond.</p>\n'}, {'answer_id': 10812, 'author': 'Tom van der Zanden', 'author_id': 26, 'author_profile': 'https://3dprinting.stackexchange.com/users/26', 'pm_score': 2, 'selected': False, 'text': '<p><strong>You can safely use the module with 24V.</strong></p>\n\n<p>The input side shows a red LED, optocoupler and 1k resistor in series. The LED and optocoupler probably have a voltage drop in the neighbourhood of 3.1-3.5&nbsp;V put together, so for a 12&nbsp;V input you will get a current of approximately 9&nbsp;mA-.</p>\n\n<p>For a 24 V input voltage the increased current will cause a slightly higher voltage drop, but even if the voltage drop remains as low as 3.1&nbsp;V the current will still only be 21&nbsp;mA. This is well within the rating of the optocoupler (similar optocouplers are often rated for 60&nbsp;mA) and slightly pushing the rating of the LED (similar LEDs are usually rated for 20&nbsp;mA) but it will probably be fine.</p>\n\n<p>For extra peace of mind you could connect an additional resistor in series with the input. The "ideal" value (that is, to keep the current identical to that at 12&nbsp;V) would be 1.3&nbsp;kΩ, though any small value resistor (above 100&nbsp;Ω) would be fine.</p>\n'}]
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