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Did you make a robotic coffee pot which implements HTCPCP and decafs unauthorized users? Show it off here!
By marcus_erronius
#187373
Hi,
I'm a bit new to this stuff, so please go easy on me :-)
I'm making a cold-brewer for coffee to go in my fridge. The plan is to essentially hook up a milk frother (it's kinda like a low-powered hand mixer) to a switch that turns it on intermittently—giving the grounds/water a good 3-4 second stir—every hour or so. What I'm looking for is a way to make a circuit that acts like a blinker, but is tunable to allow things like a four second power-on every hour. It doesn't have to be precisely timed, just get reasonably close, so it can stir my coffee :-)
I'm probably missing something obvious, but every way I googled it, I just came up with car turn signal or windshield wiper repair how-tos :-/
Thanks!
By sterretje
#187422
I've been out of electronics for 15 years but what you're looking for is called astable multivibrator.

You don't need a microcontroller. You might be able to do this e.g. a NE555 to generate a PWM with a very short HIGH time and a very long LOW time. I'm not sure what the minimum frequency can be with the NE555. Add some additional electronics to be able to handle the motor current.

See e.g. http://www.electronics-tutorials.ws/wav ... lator.html

I'm not sure what the maximum ratio can be; the above link contains formulas so you can try to figure it out ;)
By Cannibal
#187450
You might be able to make the 555 do it with a long period by adding a counter and an AND gate after, before the motor driver.

Set up the 555 to generate a pulse train with a period roughly equal to how long you want the motor to stir for, pass that to an up counter that has its outputs wired to an appropriately wide AND gate that then goes to the motor driver. Every time the counter reaches full, the motor will activate for one count before powering down for the other N of M counts.

Going the 555 route is a good choice if you want to design such a device. Going the microcontroller route is a good choice if you want a starter level microcontroller project - I would advise a PIC10 or PIC12 as this is right up their ultra low cost alley.