Contract Work - 2 Power supply designs and motor controller circuits

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#1 - I'm looking to run a small motor (probably 200 mA typical with a max of 350 mA) for around 0.25 seconds every 60 seconds.  This system will be on a 600 RPM shaft so weight is important.  I think 2 AAA batteries would work, but if you have better battery solutions I'd be open to ideas.  Run time should be over 15 hours for whatever batteries are chosen.  I will use an ATtiny45 as the micro controller and can switch it into deep sleep between motor pulses.  For a bi-direction motor controller I'm open to recommendations, but I did some searching for this already and like this http://www.mouser.com/ds/2/308/ENA2018-D-462841.pdf so if that looks good lets just use it.  This could either be designed to use a charge pump or not.

#2 - I'd like to get a basic comparison of costs for these two options.  4 NI-MH AA batteries system with recharge circuit via USB.  Versus  lipo rechargable battery system.  So you'd need to have a basic circuit for both to get this price estimate.  Output of either system should be 3.3V with a max of 1A.  Power needs to be pretty clean here so a high switching speed would be nice.  Once we choose one then you'd design the circuit.

I would mainly like a BOM and kicad circuit for each of these.  I can then integrate these sub-systems into my larger kicad circuit.  If kicad is a problem you can provide other formats and I'll implement in kicad, but I prefer kicad.

When applying please give me an estimate for your cost to design these circuits or what additional info you need to make a price estimate. 

Both of these are for different open source projects so you must be willing for your designs to be open source and I will give you credit in the project credits if you want.

Please send applications to: maurice 'at' dreamingrobots.com

I am also happy to answer questions on this page.

[mribble]

Good questions.  Here are the answers:

Run time over 15 hours: is that motor running time or wall clock time in which the motors only run every 1/240th of the wall clock time?

I'm talking about clock time.  So in these 15 hours the motor is only running for about 4 minutes.

Weight is important: You mention several kinds of somewhat heavy battery packs, but then mention the weight concern.  Do you envision the motor driver and battery pack and motor and all circuitry and wiring being on the moving shaft or do you expect some of that to be connected by cable / slip ring coupling / etc. away from the shaft?

Everything you mentioned goes on the shaft.  I'm very open to other kinds of lighter batteries.  I looked at coin cell batteries, but they weren't practical due to their low current output.  Maybe with a current pump they would work (I haven't calculated how large the caps would need to be to make a current pump work).  I think 2 AAA batteries might work as long as I balance everything well.  So that's why I put them down, but if you can figure out a way to make something lighter work that would be great.  To help understand what is being designed I'm basically planning to do an automated way of moving these yarn hooks on this electric spinning wheel I designed.  https://www.kickstarter.com/projects/1492884446/electric-eel-wheel-5

A small motor: What's the requirement?  Do you have one selected?  What types are acceptable with what performance?  Are you considering permanent magnet DC or BLDC or ...?

I don't have a motor selected yet, but I was expecting it to be a bidirection DC motor.  I used some of these for prototyping (https://www.amazon.com/gp/product/B01J04KK38/ref=oh_aui_search_detailpage?ie=UTF8&psc=1) -- you can get them for much cheaper from china.  But they actually gear things down too much and used some laser cut gears to speed things up.  My plan for the final product is to do the gearing myself, but the prototype of this mechanical system worked well enough for me to have a high confidence that I can make that part of things work.  I was planning to just find a 3-6V motor from http://www.jameco.com that is about the right size hand has the lowest RPMs and using that.

The only part of the electrics I didn't mention so far is there will be a shut resistor to detect current usage by the motor.  That's how I'm planning to detect when the hook gets to one end.  The current spikes and I switch the motor direction.

It sounds like you're talking almost more about the battery pack to DC voltage regulation and maybe battery charging than you are about any other aspect of the circuit.  If you use your AT Tiny MCU to turn on and off the motor on schedule then what is the "motor controller" doing?  Does the motor need to be speed sensed / controlled by a sensor / circuit or is open loop OK with maybe just no control or constant voltage or constant current type control?
Simply apply a stiff voltage source within rating to a DC motor and it'll run at a speed depending on its load.  So a power switch is all that's needed there absent other unstated requirements.  BLDC motors on the other hand need lots of control circuitry relatively speaking.

The reason I'm talking more about battery and power is because that's the part I don't have working in my prototype and haven't done before.  Full speed and open loop for the motor is fine.  The only special requirement is that I need to be able to switch the direction of the motor.  I thought about driving directly with mosfets, but thought that h-bridge controller would make things smaller and easier to design.  If you'd rather design this part of the circuit differently I'd be open to that.

If we get the right motor and batteries maybe the motors motor's power doesn't need to be regulated.  I think that's what you might be getting at and that does seem like a good idea if we can make that work.

I mentioned the shut resister earlier will be used to detect a motor stall and switch directions.

#2

So you want battery pack in and 3.3VDC 1A power output.  Ok.  Is there a reason you don't use an off the shelf battery / DCDC power module?  I guess with possible charging as well as regulation custom could make sense from a customization perspective if not a cost one.]So you want battery pack in and 3.3VDC 1A power output.  Ok.  Is there a reason you don't use an off the shelf battery / DCDC power module?  I guess with possible charging as well as regulation custom could make sense from a customization perspective if not a cost one.[/url]

I expect to make around 1000 of these for a future project so I don't want to use a module.  I started looking at boost/buck converters and the only one I found was

It would work great, but I have had issues with QFN packages in the past so I'd prefer an easier to solder package (mainly one you can see if something is wrong).  Then I started looking at using boost in SEPIC mode and realized there must be people who understand this better than I do and can help with it.  I'm mostly a software guy and am busy with some Android and embedded micro controller code for this project.  I'd rather just have someone else help here (though I will want to understand how it works before I ship).

There is also a discussion about this going on here (https://www.eevblog.com/forum/beginners/help-selecting-switching-power-regulator/).  I was planning to just do it myself, but decided it was going to take up so much time that I started this thread.

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I've been thinking about this more and here is a better definition of one of the projects (I've decided to put off the second design for now since they aren't as closely related as I initially thought).

I'm working on a future add-on for this Kickstarter I did (https://www.kickstarter.com/projects/1492884446/electric-eel-wheel-5).  If you watch that 3 minute video you'll see there is that center piece that spins (called a flyer).  There are some hooks on it that you need to move by hand.  I've done some prototyping of the mechanical system that moves these hooks with a small motor and am happy with those results.  This project is to help design the circuits and electronics that will move this hook.

Because this will be on a rotating shaft I want to design everything to be light weight.  The motor will pulse on to full power for half a second every minute.  For that half second it will run at around 100 mAH at 5V, but if you could smooth out that current draw it would only be about 1 mAH at 5V.  So what I think we should do is slowly charge a super capacitor for 1 minute and then discharge it to run the motor for half a second.  With this kind of a slow charging circuit we should be able to use 2 coin cell batteries like CR2032.  My estimates is that 2 of those should last around 200 hours (1 mAh discharge and 225 mAh batteries) which is more than enough.  I would expect you to double check all my estimates and confirm a design like this should work.

Here are the major components you'd need to design into the PCB:
1) Bidirectional motor controller
2) ATtiny45 microcontroller and programming header
3) On/Off switch
4) Shunt resistor attached to an analog input.  Software will detect when the motor starts to stall and switch motor direction.
5) Battery holders
6) Power regulation (5V for both micro and motors is probably fine)
7) Super capacitor to run the motor (I calculate around 50 mF) and a circuit to charge it from the batteries.

I will write software for the ATtiny and plan to put it into a deep sleep mode for 1 minute while the motor controller isn't running to save power.  I would expect the power usage from this micro to be small compared to the motor.

Here is the motor I plan to prototype with: https://www.pololu.com/product/2365

The PCB should use 0804 and larger SMD components and be a 2 layer board with 8 mil+ traces.  All the components should be placed on a single slide.  If needed some of the components can be through hole.  Delivery would be a schematic and board layout in Kicad.

I have designed circuits like this in the past, but just don't have time to do this myself right now.  I should be able to define any big holes you see in this, and would like to agree on a design before you make the kicad files.  I feel this is a well defined project and in the end should be a pretty simple PCB.

If you're willing to do this for a fixed cost I'd prefer that.  Otherwise please include an estimate of hour hours for this project.