Need Help On My Feet w/ A Little Home Project

Hello,

I'm a mechanical engineer of 5 years and have recently come up with an idea for a device that I want to put to test. I've modelled all components in 3d cad, and have fabrication figured out... I just need assistance with electrical. In school I took Circuits I and II, and there is a bit I remember, but its embarrasing how much I forgot - which has brought my confidence level down. I have done alot of home wiring jobs and engine harness wiring jobs on cars - but never circuit design.

What i'm trying to do is to create a 120VAC device that operates a small microwave turn-table motor [rigged to a pulley system] for a duration of time (say three minutes) per three [user-inputted] set times (say 2:00AM, 8:00AM, 10:00PM). If it is much simpler to have a timer on an 8-hr delay that would be fine too.

I wish to make this an in-door "appliance" which is safe, basic, and reliable.


Please help guide me in the right direction in terms of component selection (where to buy) and any hints to a basic circuit would help too - or a tutorial on how to sketch something so simple.

Thanks

How accurate does the 8 hour period need to be. Can it drift a bit or do you need it to be clock accurate ?

3v0 said:

How accurate does the 8 hour period need to be. Can it drift a bit or do you need it to be clock accurate ?

Click to expand...

Thank you for the response - accuracy is not important. Even a drift of 10 to 30 minutes will not matter.


The cheaper I can build this thing, the better.


EDIT:

If the timer can change to operate every 4 hours (6 times per day, that would be preferred too.)


Also, there is an addition I failed to mention to this circuit:

I'd like to incorporate a tiny 120VAC to 12VDC transformer to operate an automotive two windshield pump and a 12VDC computer fan. I can take it from the circuit design positive/negative of the 12VDC transformer. Power to the transformer would come on when the power to the microwave-turn-table motor comes on. Simple enough I would think?

How small does the AC-to-DC converter have to be? Can you use a small computer power supply? That'll give you 12VDC, 5VDC, and 3.3VDC and probably all the wattage you need to drive a few small motors. You can get low-end ones pretty cheap.

Hi,

For a very variable programmable timer with user input probably the best way to go is with a micro controller. You can connect a keypad for all the user input and variability you'll ever need. Time every 1 hour, 1 hour then two hours, 5 hours off, 1 minute on or 100 minutes on, etc., just about anything the user wants to enter.

If you dont like that and you have a small number of events and not too variable, you can use multi position switches to select capacitors or resistors for a timer IC chip, or a variable resistance (potentiometer) to vary the time duration and another to set the 'on' time. That shouldnt be too hard to do.

For the DC power supply you can probably just use a wall wart.

Thanks.. The 12VDC is something I think I can handle on my own. Any input or help to the actual 120V system (ie what timer i could use, where i could get it, how I can have the timer enable the voltage input to the turn-table motor, etc)?

Are you thinking of switching things on and off at the 120VAC source? Probably not the right approach here. You want to do everything downstream of the 12VDC source.

What MrAl was getting at above is using a microcontroller (or other IC timing hardware) as a timer. The timer circuit will activate a relay or transistor to turn the motor(s) on and off. See the attached diagram to get an idea of what we're recommending. This will require putting together a small circuit on a breadboard and possibly some microcontroller programming (if you want to go that route).

So it sounds like you already have a way of getting a 12VDC source that can handle the necessary wattage to drive those motors (if you're not sure about that, please ask!). Your next step is to decide whether you want to go the microcontroller route or IC timer route. The microcontroller will be simpler circuit, but require programming. An IC timer will be a larger circuit, but no programming.

Rusttree - thanks. The Microwave motor is actually 110VAC... I may not even wish to use any 12V parts.. I just want to get the motor running on a timer first.

I guess what I was I should have said in the first post is that I am not electronics savvy and I am ignorant as to where and what to look for in terms of components. Additional help and "hand-holding" is much appreciated!

Would this work?

My twopence.

Firstly microwave turntable motors can be handy, one of thier syncracies is that the direction on power up is random, and if you stall or overload them they will start in the opposite direction (seen this on disco light effects).
I have a few old electric clocks which have a similar design motor, they have a spindle at the back that you twiddle on power up to make sure the clock goes the right way, sometimes they'll start backwards.

I've seen a few articles in electronics magazines and a couple of kits or ready made boards for multi function timers, you could start with one of these, allthough it'd be a lot easier with something like the one above, you can get these designed to fit nicely into a case for use with central heating boilers.

Hi again,


For versatility my first choice is a microcontroller, you'd have to get a programmer and read up on them. One chip and that takes care of the whole project other than a couple relays or triacs.

Second choice is to use 555 timer ICs and maybe some CMOS logic counters. Maybe you should look up the 555 timer and see if it looks like something you'd want to work with.

If you give us a clue on what you are trying to accomplish We might be able to give you a better solution,
I know you said the cheaper the better.
But a small micro-controller would be the best way to go like a arduino and you can set it up anyway you want.

you can get a Arduino for $26.00 and a 2 channel relay board for $4.00

I think Mike has the easiest solution. Here is one that can have on and off times of 1 minute. Doubt if you could make one for $20.

**broken link removed**

I think you can find the turntable motors on E Bay as well.

**broken link removed**

Dunno if you can astill get them now, some of the old time machines I maintain have cam timers, a motor very much like the microwave turntable motor drives a drum, on the drum are moveable knobs that operate micro switches around the outside of the drum, they used to use them for sequencing before plc's and micro's beacme popular.
Rs comps used to do a kit where you got a motor/drum and switches and some gears so you could select the speed you wanted to go at from a minute to 24 hours.

Very old hat technology for the folks on this forum.

You being into the very different world of mechanics might be able to integrate a cam timer into the system you described in your first post, I dont know exactly what your planning, but its worth considering.

dr pepper said:

My twopence.

Firstly microwave turntable motors can be handy, one of thier syncracies is that the direction on power up is random, and if you stall or overload them they will start in the opposite direction (seen this on disco light effects).
I have a few old electric clocks which have a similar design motor, they have a spindle at the back that you twiddle on power up to make sure the clock goes the right way, sometimes they'll start backwards.

I've seen a few articles in electronics magazines and a couple of kits or ready made boards for multi function timers, you could start with one of these, allthough it'd be a lot easier with something like the one above, you can get these designed to fit nicely into a case for use with central heating boilers.

Click to expand...

I need the shaft of the motor to go in only one direction. This may present a problem. Can this be prevented to make the shaft be unidirectional?

dr pepper said:

My twopence.

Firstly microwave turntable motors can be handy, one of thier syncracies is that the direction on power up is random, and if you stall or overload them they will start in the opposite direction (seen this on disco light effects).
I have a few old electric clocks which have a similar design motor, they have a spindle at the back that you twiddle on power up to make sure the clock goes the right way, sometimes they'll start backwards.

I've seen a few articles in electronics magazines and a couple of kits or ready made boards for multi function timers, you could start with one of these, allthough it'd be a lot easier with something like the one above, you can get these designed to fit nicely into a case for use with central heating boilers.

Click to expand...

Can this be prevented so that the motor can be uni-directional only? If not then this would be a problem.

Hi,


I rebuilt a microwave turntable motor once, i couldnt see throwing out the whole mic just because the motor stopped turning. As it turns out, removing a few turns from the motor winding and it was up and running again. It went bad because of water that boiled over and got into it and damaged it just enough to stop it from working anymore.

Unfortunately i didnt experiment with it that much, but what i think happens is the armature can stop in several different locations when it is turned off. Depending on where it stops, that dictates which direction it will start when the power is again applied. If you can force the shaft to be in one particular orientation before starting it, it may start in the same direction all the time.
This might be easy to test. Simply mark the shaft, mark the same on the motor body. Start the motor, then turn the shaft back to that exact angle so the marks line up again. Start the motor again. If it turns in the same direction as before, that proves this works. If fails even once out of 100 times it may not be a good idea unless you can deal with that. But keep in mind that you may have to try several different 'marked' angles to get it to work because there might be less tolerance for some angles than others, so some angles may prove to be reliably repeatable while others not very good.
If you try this please post results back here.

I had one older mic that always turned in the same direction and was very surprised when i got a new one and it turned different ways sometimes. I was thinking, "Gee, didnt this thing used to turn clockwise?" I eventually realized it had a mind of it's own. Chaos at work

View attachment 64269

Here is what i'm trying to make.

Hi,

Is that all it has to do is open a flap or does it do other things too?

Reminds me a little of a pet feeder.

Later ferranti clocks had an 'auto start', comprising two things, an inertia rotor in the motor, this pulled in laterally when power was applied, and also when the rotor pulled in the end of the shaft slid past an archimedes cork screw type arrangement forcing to start in the right direction.

In my heath robo 'leccy style bodging for a prototype I'm thinking maybe a modded 1/4" drive ratchet fastened to the other end of the motor shaft stopping rotation in one direction, making the motor go the right way every time, at least then you'd be able to switch directions.
Maintaining direction electrically would entail rewinding the motor at the very least, and you dont want to do that, I've rewound a few old electric clocks to run off low voltage ac wall wart supplies, there are zillions of turns on these things, your micro motor will be similar.