Working on a PCB to PWM a bunch of MOSFETs with a STM32 - Page 1
Forum section: electronics / projects

author: dholth
author_rank: Newbie
timestamp: January 02, 2016, 06:40:35 am
content: Hi there, I was wondering if you all could give me some feedback on my latest hobby electronics project.I thought it would be fun to try to replicate Epcot's jumping water fountain at a very small scale, so I bought some cheap pumps and have been designing a microcontroller + power mosfet board that should be able to PWM 12V@350mA * 8 through 0.05 Ohm FETs. The board is 50mm^2, designed to fit inside a Hammond 1593K box, includes a buck regulator to provide 3.3V to a STM32 microcontroller, RGB LED in the corner, button, clock crystal, 4 JST PH connectors on either side plus a green terminal block for DC input. Most complicated thing I've attempted so far. How do you like it?I think it will probably be fine to route the input voltage around the outside of the board. The board has a virtually unbroken ground plane.Not sure about the 750mA polyfuses on each set of 4 outputs. Better than nothing but the trip current of 750mA @ 12V is a decent amount of power. Yes I'm currently living dangerously without reverse polarity protection.Think I can get away without big caps to bypass the motor outputs and just let the them take the ripple?Will be interesting to listen to the buck regulator on an AM radio. How do I know whether it should it have a common mode choke, a ferrite bead, or some other kind of filter?Loving KiCad's new push-and-shove router by the way.Thanks,D

author: SL4P
author_rank: Super Contributor
timestamp: January 02, 2016, 07:32:32 am
content: Not critiquing your PCB, but I think the 'real' water displays use a single pump, plus an accumulator to ride through pressure variations (with none, one or more valves open simultaneously) - and simple solenoid valves to manage each fountain squirting!(Vcc on outputs is not defined anywhere else ? Should be a 'dirty' rail - as not to upset the CPU etc!)(Personal preference - put outputs on the RHS of the schematic - it makes 'following' signal flow more intuitive)Fancier displays use proportional valves with more pumps & larger accumulators.Please post a video when you get something running - it sound like a fun project!

author: dholth
author_rank: Newbie
timestamp: January 05, 2016, 04:16:59 am
content: Oshpark time. One important addition - flyback diodes across the outputs. I did think about doing solenoid valves, but if you want to go really small I think tiny pumps are more practical.

author: Fungus
author_rank: Super Contributor
timestamp: January 05, 2016, 04:28:17 am
content: Quote from: dholth on January 02, 2016, 06:40:35 amWhy do you need PWM?

author: SL4P
author_rank: Super Contributor
timestamp: January 05, 2016, 04:36:55 am
content: PWM cab useful for 100% pull on, followed by 20% hold current...

author: dholth
author_rank: Newbie
timestamp: January 05, 2016, 01:08:21 pm
content: It will be individual motors like in this video.

author: BradC
author_rank: Super Contributor
timestamp: January 05, 2016, 02:01:49 pm
content: I have a couple of those little pumps set up as bath toys for my little one. Cheap, adequate, cheap, cheap & cheap.That is a very cool application. Keep us posted!

author: dholth
author_rank: Newbie
timestamp: January 25, 2016, 05:20:16 am
content: Blinky unlocked! Buck converter happily converts 5V - 20+V to 3.3 for the micro, and it's running a modified blink demo from the amazinghttps://github.com/andysworkshop/stm32plus(C++) library.