# Low voltage on pin 11 for laser **URL:** \ **Category:** Upgrades\ **Created:** [February 11, 2017, 5:13pm UTC](https://community.inventables.com/t/low-voltage-on-pin-11-for-laser/33956 "2017-02-11T17:13:40Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![GarethWhittock](https://avatars.discourse-cdn.com/v4/letter/g/4af34b/32.png) [@GarethWhittock](https://community.inventables.com/u/GarethWhittock)\ **Post date:** [February 11, 2017, 5:13pm UTC](https://community.inventables.com/t/low-voltage-on-pin-11-for-laser/33956/1 "2017-02-11T17:13:40Z")
Hi all, I’m trying to set up a laser using pins 11 and 14 controlling the Jtech 2.8 watt upgrade. I’m issuing the M03 and M05 commands using the macro function on UGS. When I do this, pin 11 only shows about 120 mili volts which goes down to 0 volts on an m05 command. Any ideas? Cheers, Gareth ---
**Author:** ![JustinBusby](https://yyz1.discourse-cdn.com/flex009/user_avatar/community.inventables.com/justinbusby/32/30906_2.png) [@JustinBusby](https://community.inventables.com/u/JustinBusby)\ **Post date:** [February 11, 2017, 5:18pm UTC](https://community.inventables.com/t/low-voltage-on-pin-11-for-laser/33956/2 "2017-02-11T17:18:59Z")
What S parameter are you sending? Try sending a “M3 S12500” command. Most likely what you’re seeing is the PWM scaling of the spindle output. Are you using the Jtech GRBL version or the Inventables GRBL version? ---
**Author:** ![GarethWhittock](https://avatars.discourse-cdn.com/v4/letter/g/4af34b/32.png) [@GarethWhittock](https://community.inventables.com/u/GarethWhittock)\ **Post date:** [February 11, 2017, 5:50pm UTC](https://community.inventables.com/t/low-voltage-on-pin-11-for-laser/33956/3 "2017-02-11T17:50:53Z")
Thanks for getting back Justin. That command works! Can you tell me why it’s different to the M03 command? I guess I’ll have to edit all my Gcode to account for this do I? Thanks ever so much for your help though. Gareth ---
**Author:** ![JustinBusby](https://yyz1.discourse-cdn.com/flex009/user_avatar/community.inventables.com/justinbusby/32/30906_2.png) [@JustinBusby](https://community.inventables.com/u/JustinBusby)\ **Post date:** [February 11, 2017, 5:54pm UTC](https://community.inventables.com/t/low-voltage-on-pin-11-for-laser/33956/4 "2017-02-11T17:54:28Z")
The S parameter sets the spindle rpm value. For a spindle, you set the rpm value with the level of the pwm out. The newer version of GRBL has a variable for max/min rpm so you can set it to be 1 so a “M3 S1” to turn on completely. ---
**Author:** ![GarethWhittock](https://avatars.discourse-cdn.com/v4/letter/g/4af34b/32.png) [@GarethWhittock](https://community.inventables.com/u/GarethWhittock)\ **Post date:** [February 11, 2017, 6:01pm UTC](https://community.inventables.com/t/low-voltage-on-pin-11-for-laser/33956/5 "2017-02-11T18:01:23Z")
So would you suggest that I get a newer GRBL version? I want to produce grey scale type work. Isn’t that where the pwm capability comes in? As you’ve probably guessed - I’m a complete novice… You’ve made my evening - I’ve been on this all day! Gareth ---
**Author:** ![JustinBusby](https://yyz1.discourse-cdn.com/flex009/user_avatar/community.inventables.com/justinbusby/32/30906_2.png) [@JustinBusby](https://community.inventables.com/u/JustinBusby)\ **Post date:** [February 11, 2017, 6:06pm UTC](https://community.inventables.com/t/low-voltage-on-pin-11-for-laser/33956/6 "2017-02-11T18:06:39Z")
I don’t deal with the laser. @LarryM should be more helpful concerning that. ---
**Author:** ![LarryM](https://yyz1.discourse-cdn.com/flex009/user_avatar/community.inventables.com/larrym/32/51450_2.png) [@LarryM](https://community.inventables.com/u/LarryM)\ **Post date:** [February 11, 2017, 6:50pm UTC](https://community.inventables.com/t/low-voltage-on-pin-11-for-laser/33956/7 "2017-02-11T18:50:40Z")
I have modified 1.0c grbl to support the JTech laser. I would recommend that you download and install it to make working with the spindle and laser more convenient. Even easier to use if you also get a PicSender license. [.hex link](https://community.inventables.com/t/xcarve-jtech-grbl-update-11-12-2016/28943) ---
**Author:** ![GarethWhittock](https://avatars.discourse-cdn.com/v4/letter/g/4af34b/32.png) [@GarethWhittock](https://community.inventables.com/u/GarethWhittock)\ **Post date:** [February 11, 2017, 7:03pm UTC](https://community.inventables.com/t/low-voltage-on-pin-11-for-laser/33956/8 "2017-02-11T19:03:12Z")
Cool. I’ll give it a go… Thanks Gareth