[Putting this back on-list]
On 11/01/2017 11:52 AM, Chris Albertson wrote:
On Wed, Nov 1, 2017 at 8:40 AM, John Morris <[email protected]
<mailto:[email protected]>> wrote:
On 11/01/2017 10:15 AM, Daren Schwenke wrote:
When switching peltiers between heat/cool mode you can get some
really high currents.
I don't know much about it. This one is rated 48W/12V, so I used a
cheapo L298N module, 2 channels at 2A/channel, wired together. (I'm
not sure if that's allowed, but it seems to work.) Do you mean
higher current than 4A?
The L298N uses internal bipolar transistors. The device drops some
volts and burns up a lot of energy in the process. I would go with any
MOSFET based h-bridge rather then the L298. The298 has been obsolete
for years. Ad will require a big heat sink and I think a fan. A
modern device will not require a heat sink and not get hot.
I picked that one because they're available cheap on a PCB with extra
circuitry marketed to the Arduino folks. It does come with a heatsink,
and it's near the Peltier fan in my box.
I'm not married to the thing, though. If there's another solution
that's better and not much harder, let me know. There's a
VNH2SP30-based (datasheet [1]) "Monster Moto Shield", 30A MOSFET, for
example.
[1]: http://www.st.com/resource/en/datasheet/cd00043711.pdf
I don't understand the use of Machine Kit for this. Everyone else
builds these using a $1 micro controller. It is actually MUCH easier.
This is the perfect project o use one of these $3 STM32 boards
Perhaps this is just an exercise?
The value IMO is in the demonstration of a full integration from
electronics to remote GUI, and in the overall simplicity for learners.
Maybe it's the lesson that comes after Alex's AND-Demo.
I know enough about microcontrollers to know the basic control functions
could easily be done on an STM32 board, and there's probably enough
memory to do some logging, too. I'd believe if you said there's a good
way to build a network-connected remote interface and (maybe even
cross-platform) GUI, and $3 is a fantastic price point (the BB WiFi
adapter cost more than that). You're right, the value of this project
can't be judged by the efficiency of using Machinekit on a Beagle for a
thermostat. I still hope there's value in the lesson, and anyway, like
that guy in True Grit using a horse pistol to shoot rats, it's fun.
Actually, this is really my first GUI ever, and my own eyes were
certainly opened. With haltalk and QtQuickVCP, the whole GUI took zero
lines of code outside the remote comp's ~dozen python lines to create
pins. Really amazing stuff.
John
--
website: http://www.machinekit.io blog: http://blog.machinekit.io github:
https://github.com/machinekit
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