# Exhaust Fan Removal/Replacement on the Glowforge

**URL:** https://community.openglow.org/t/exhaust-fan-removal-replacement-on-the-glowforge/251
**Category:** Technical
**Tags:** how-to
**Created:** [July 21, 2018, 4:42pm UTC](https://community.openglow.org/t/exhaust-fan-removal-replacement-on-the-glowforge/251 "2018-07-21T16:42:10Z")
**Posts on this page:** 1
**Showing post:** 44

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### Author: ![ScottW514](https://community.openglow.org/user_avatar/community.openglow.org/scottw514/32/5_2.png) [@ScottW514](https://community.openglow.org/u/ScottW514)
#### Post date: [May 8, 2020, 4:39pm UTC](https://community.openglow.org/t/exhaust-fan-removal-replacement-on-the-glowforge/251/44 "2020-05-08T16:39:05Z")

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> [@Peter](#):
>
> Don’t I have to worry about the PWM pulse causing chatter on the relay?

This is what the “fine print” on my response was referring to.

Glowforge doesn’t do any speed control for the exhaust fan. They set it to full blast. For the PWM output, this means either 0% (off) or 100% (on) pulse width. You shouldn’t get any chatter.

You would want to set the IN to trigger on HIGH, assuming you want to fire the relay when Glowforge commands the exhaust fan to turn on. The output voltage level on the PWM is only 3.3V, IIRC. That _should_ probably be enough to trigger those devices.

**NOTE: Be VERY careful about what you hook up to that PWM line**. There is _ZERO_ input protection on _ANY_ of the IO pins on their factory control board. If you accidentally put 12V into the PWM output, you WILL fry the microprocessor (I know this from personal experience).

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