Greetings.

I am working on a prototype of a small, portable device powered by a very small PV cell trickle charging a capacitor array. I'm having problems finding the right part to use as a status indicator, however. LEDs draw too much current for this device. I'm imagining a very small rotary motor or actuator which steps forward with each capacitor discharge. The motor's load will be a small color-coded plastic strip. It only needs to complete one revolution per day.

Does anyone have any ideas about a low-cost solution to this problem?

Many thanks.

 

A small short stroke solenoid in series with cap discharge load. Plunger actuates paul & ratchet wheel.

 

I'd try stripping the motor & gearbox out of a battery clock, the type that run on a single cell.

I think those motors generally use a bipolar pulse, ie. one polarity then immediately the other, to complete one step; effectively, a one-pulse stepper with gears to reduce each step to 1/60th of a turn for the hands.

With a battery life of a year or two, they must be pretty low power!

 

Wow. These are both excellent suggestions, and both of these solutions look viable.

I can't believe I hadn't thought of the clock mechanism. What a great idea .

Regarding solenoid/ratchet wheel: I'm finding lots of places offering ideal solenoids, but has anybody got any insight as to where one can purchase the pawl/ratchet/wheel assemply?

Thank you both enormously.

 

has anybody got any insight as to where one can purchase the pawl/ratchet/wheel assemply?

Yeah.. pawlRatchets.com


I had to slide the aprilfooljoke in there. sorry.

 

Would need to know more about load to suggest solenoid or relay to use. Ratchet wheel - small gear, plastic or metal; looking at one from dead VCR, 33 mm dia, 39 teeth, 2.6 pitch would allow 39 pulses per revolution, with a stroke of about 3.5 mm. Pawl from beer can Al.

 

With a 48 tooth, 5 cm gear, prototyped a ratchet wheel using sewing pins, foam board, two strips of beer can, & 4.5 ohm solenoid. Drive is 1000 uF cap charged via 9 V battery & 220 ohm resistor = one count per pulse.