Advice on Schematics - Brewing Mash/Fermentation Controller

Other Hardware General Electronics
1

Hi all, I've got various cobbled together controllers for my homebrew outfit - one controlling a fermentation fridge, another looking after a mash controller. I'm designing a new unified system with one LED/Keypad control unit - I was wondering if anyone could cast an eye over my 12v / logic level boards and offer observations?

Just so you can find your way around the diagram. The two wire on the left bring 12v in to the system. This is dropped to 5v by the thing labelled Traco and set to power the Arduino. The stuff in the bottom left I'm trying to use a Mosfet to offer 0v-12v to a pump (thus varying its speed) based on PWM. I'm least sure about that bit - I've not really used mosfets before. The circuitry to the right of the nano is for the LCD/Keypad - I've got that working.

Thanks for any advice!
Mark

BrewLab v2.0_bb.jpg
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2

It's recommended that you use a 100 ohm resistor between the Arduino and the mosfet gate, especially when using PWM. This is to limit the peak current to/from the Arduino pin when charging the mosfet gate capacitance. Otherwise, looks OK to me. Do you really need the 3.3K pullup resistors - have you tried using the internal ones?

PS - also I suggest connecting a large decoupling capacitor across the 12V supply, -ve end connected close to the mosfet source terminal and +ve end connected close to the junction of the motor +ve terminal and the diode. Maybe 1000uF 16V.