Very low power miniature motor control
Very low power miniature motor control
(OP)
I have a problem I'm trying to solve and hopefully someone may have some suggestions here. I am designing a control circuit for a 6mm 1.2V DC motor. I'm using a pic 10F222 to control turning on and off the motor. I want to turn on the motor when I detect the shaft rotating and turn off the motor after a period of non-rotation. I can do this with a magnetic reed switch and a small magnet mounted on the shaft but the lifetime of the reed switch is limited. Also I want to power the whole thing from a 357 battery and it needs a 6 month shelf life. I have a 37uA power budget when idle. I don't have an on/off switch so it's always powered. I am looking at a Holtek HT7727 switcher to power the pic. The problem is figuring out how to detect when the shaft is turning. I need to generate an interrupt to the pic to wake it up and I also need to figure out if the shaft is stopped, moving slowly or free running.
Thanks,
Steve
Thanks,
Steve





RE: Very low power miniature motor control
RE: Very low power miniature motor control
resolver
hall sensor
back emf
TTFN
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RE: Very low power miniature motor control
I looked at hall effect sensors but they are too power hungry. The back emf is only about 20mV so amplifying it to a usable level would kill my power budget. A dry contact closure once per revolution would be ideal.
RE: Very low power miniature motor control
You mention the current drawn when off, but not when on. If the life of a reed switch is inadequate then any mechanical switch is also out. That would include a rotary shaft encoder with brushes. An optical encoder would be pretty power hungry.
The motor back emf can be increased in voltage without an amplifier. Use a transformer!
RE: Very low power miniature motor control
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Very low power miniature motor control
CD players (audio) used to have a tiny switch often made from two sprung copper leaves which detected when the tray came off its fully extended position. This initiated the tray closure. Don't know if things have changed since those days - that was a quite a while ago when fixing the things was cheaper than replacing them!
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Sometimes I only open my mouth to swap feet...
RE: Very low power miniature motor control
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Very low power miniature motor control
A reed switch has something like 10^8 cycles life. And yor device does not seem to need to be working more than every tenth second or so.
That translates into a little more than 30 years. That's a lot longer than most gadgets live these days.
BTW, I have used PIC processors in remote measuring devices that run from batteries and my mean current consumption was 13 uA for a fairly complex circuit that measures temperature, supervises 230 V AC, a few switches and also "takes the line" when you phone it. So, I think that you should be able to shave a lot of current consumption off that application.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Very low power miniature motor control
I'm not sure if the PIC input needs a pull-up though. The datasheet says a weak pull-up is 250uA. That would eat up the battery pretty quick.
Thanks,
Steve
RE: Very low power miniature motor control
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Very low power miniature motor control
Look here www.cotorelay.com
RE: Very low power miniature motor control
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Very low power miniature motor control
RE: Very low power miniature motor control
I can´t remember the exact name
but their seems to be a technique where the power
drawn by an electrical motor is observed..it seems
that pulses can be observed on the power line
those pulses represent the motor-speed and are in turn
used to control the engine speed
...so it´s some kind of feedback without additional sensors
No idea if this works for all kinds of electromotors
I have seen even special ic´s for it..just don´t remember
their names...maybe looking for "fan-speed-control-ic"
will give some result
WatchJohn
RE: Very low power miniature motor control
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Very low power miniature motor control
RE: Very low power miniature motor control
Amp or switch the "signal" back to the PIC ?
but:-
enjoy trying
Don