simple first project

Thread Starter

sailingboarder

Joined Jan 25, 2008
12
so i am working on a open-ended project for school, and its my first foray into electronics
for our specific project, we want to control two motors, each multi-dimensional, so four total movements
we want them to happen in a controlled order, specifically close-in-out-open-close-in-out-open-etc.
we would like to trigger each movement by the conclusion of the previous movement
while we have figured out a way to make each motor switch direction, we have had a hard time making one motor start the other motor at the same time as stopping itself
i thought about using some sort of IC that could trigger the different flows instead of manually turning flows on and off, but i do not know if/how to do this
i stumbled upon the L298N motor chip, but i'm not sure if this is really what i need and if so, how to use it

any advice on where to look for information would greatly be appreciated
 

SgtWookie

Joined Jul 17, 2007
22,210
Can you post a schematic of what you have so far?

What kind of motors, DC or stepper?

Are they linear or rotary?

What's the voltage and current rating of the motors?

The L298 is an H-bridge driver IC. It's much easier to use if you also use the L297, but you'll still need a microcontroller or logic circuit to drive the L297.

If your motors are pretty low power, they can be driven using less complicated circuitry.
 

Thread Starter

sailingboarder

Joined Jan 25, 2008
12
we really don't have much at the moment, we are simply brainstorming ways to approach the problem
as far as a motor, we have one right now and will probably get another one of the same kind
we just bought an electronic screwdriver and ripped the casing off it so we can use the motor
its 3.6V
 

SgtWookie

Joined Jul 17, 2007
22,210
So are you planning on having this motor rotate a disk, turn a screw, swing a boom?

Since it is purely a 3.6V DC motor, you won't need very complex electronics like you would with a stepper motor.

Basically, you will have two motors, each capable of running in forward direction, reverse direction, or stopped, right?

What kind of motion did you have in mind?
 

Thread Starter

sailingboarder

Joined Jan 25, 2008
12
we want to open and close a clamp, and then move that clamp back and forth along a track
basically, we are automatically loading pencils into an automatic pencil sharpener

i revised our design using dpdt switches/relays

the thing i'm having trouble understanding about the relays is this: can i flip the relays with a current pulse, or does it have to be a constant flow of power?

i'm attaching a draft schematic, but without a way to flip the switches
 

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scubasteve_911

Joined Dec 27, 2007
1,203
What is going to monitor and control the sharpening time? Switches and relays are nearly instantanious. If you aim for a neat automatic way to sharpen pencils, then you pretty much need a method to program a process in. If you are new to electronics, you might look into a basic stamp or maybe a PLC if you can borrow one.

Steve
 

SgtWookie

Joined Jul 17, 2007
22,210
Ahh, OK. :)

Wow, that blue on the black background is hard to see!

Yes, the reversal switch will work - but you need to stop the motor(s) for various periods of time while either the other motor is running, or until the sharpener is done with the pencil. Some sharpeners show a light when the pencil is sharp - are you planning on using that feature?

Usually, relays have solenoids that are either energized to close the NO contacts and open the NC contacts, or de-energized to open the NO contacts and close the NC contacts. There are latching relays, but they're pretty expensive.

What you seem to need now are SPDT limit switches to cause one motor to stop running and the other to start running, or engage the next action in the sequence.

You also need a way to determine when to stop the thing - like there are no more pencils left to sharpen.
 

Thread Starter

sailingboarder

Joined Jan 25, 2008
12
so i've decided that we basically will just want continued motion, then i will simply set one throw of each relay to be powered when no flow through the coil and the other when there is flow through the coil, which will be alot easier than latching switches

also, i though about using a push button switch that can be pushed when the motion reaches the end of its path, like the clamp reaching the top, and it would turn on the flow that would then reverse the motion

as far as the light on the pencil sharpener is concerned, the one i have right now does not have that, but i am going out to see if i can find one at office depot - how would i use that light to send a flow to the coil on one of the relays?

thanks for all your help, i can see the project design starting to fall into place
 

Thread Starter

sailingboarder

Joined Jan 25, 2008
12
after a trip to office depot, i did not find a pencil sharpener with a light when finished, but i did find a pencil sharpener that has a sensor and will automatically shut off when the pencil is sharp
is there a way to capture this action and use it to supple power to one of the relays?
other than that, i think i i've figured out how i'm gonna make the thing work, electrically
this afternoon we're gonna start building the frame while we finalize our circuitry design
 

SgtWookie

Joined Jul 17, 2007
22,210
As far as the auto-shutoff feature of the sharpener, I haven't seen one that does that.

Opening up such an appliance will:
1) Expose you to hazardous line-level voltages
2) Void the warranty.

How much power does it use when it's operating?

[eta]
Just found this one:
http://www.officedepot.com/a/products/517304/Cordless-Pencil-Sharpener-Black/
Battery powered - runs off four AA cells (6v) auto start, auto shutoff, for under seven bucks. Sounds like just what you need.

What are you using for a power supply? A converted ATX-form factor computer supply? If so, you'd have 12v available, along with +/-5V. I have a sneaky way to get a TTL/CMOS-compatible signal out of this sharpener by using the attached circuit.
 

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Thread Starter

sailingboarder

Joined Jan 25, 2008
12
the sharpener? i do not know, we decided to skip that one and simply push the pencil all the way in slowly, then pull it out, keeping things simple
 

thingmaker3

Joined May 16, 2005
5,084
If you can put a relay coil in parallel with the sharpener motor, it will de-energize when the motor stops. Whether such configuration is possible depends on motor voltage and the relays available to you.

Always exercise caution when dealing with electricity. Don't go exploring while the thing is plugged in.
 
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