Souper man

I want to power my 2 motors seprately (6volt around 30mA). I dont know what to get or how to do it. I want the configuration to be simple, but effective. I want a output on a chip, say a 555 (pin3, roughly 200mA) and take that and make it turn on a separate supply, without interfereing. Any Ideas??? again???

 

I suggest you try measuring what your motors take! - do it under load, and under stall conditions - be prepared to be staggered when you do!. 30mA is no where near high enough!.

It's common to have seperate batteries for the motors, and for the electronics.

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Do these motors need to be reversible?

It's easy to make a dual PWM circuit with three comparators, using one as an oscillator and the other two as plain comparators, use a quad IC like the LM339.

You need to use the outputs to drive MOSFETs, also don't forget the pull-ups which I haven't included on my schematic!

Attached Images

Dual PWM.GIF (5.3 KB, 50 views)

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Souper man

under Load, it is about 50 mA. Stall is 400mA.

They do not need to be reversible, only on their own batteries

 

That's not very powerful what can you do with that?

Sorry I forgot to post the source for the circuit which I have modified.
http://home.cogeco.ca/~rpaisley4/Comparators.html

As the motor is so small a MOSFET isn't needed, I would add a small PNP transistor with a suitable base resistor to the the output of the comparator.

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Souper man

These motors are for a small, lightweight robot, if you were wondering which, search spagetti 2.0 in the search thing. So by using your circuit, the motors will be on their own power supply (4AA batteries)? The circuit itself will run on a rechargeable 9v (150mA), but the motors will drain it quickly, so They must run on the 4 AA power supply.

 

Souper man

The link isnt very helpful, because I still dont get how I will be able to use that for a seprate power supply...

Also, forget the 555 timer and all the component stuff. I just want my motors to draw on their own batteries. They only need to go forward.

 

I posted the link for copyright purposes as I modified a circuit taken from their website. Also one of the images on there are helpful.

Running it from a separate power supply would be easy, the comparators have open collector outputs don't they?


Therefore all that's required is for you to connect a PNP transistor in series with the positve supply to the motor and connect its base to the output of the comparator. When the comparator's output transistor turns on it will connect the base of the transistor driving the motor to 0V turning it on. When the comparator's output transistor turns off no current will flow so the transistor driving your motor will also turn off.

EDIT:
My previous atachment contained an error; I've fixed it for you.

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Souper man

so the collector goes to the motors + terminal and the - just goes into the - side of the 4 AA? Also does the emitter go to the 4AA battery supply? What about the Comparator? would one side go to ground and the other goes to the circuit that turns on the motor (output of chip x)?

If so, This is very easy and if you verify it i will experiment with it. Also, could i replace the transistor with a mosfet? not that i will, but for future robots.

THANK YOU SO MUCHS

 

No the emitter goes to the + terminal of the hgher supply voltage; remember it's a PNP transistor not an NPN transistor.

The both the supplies need a common 0V rail. The comparator needs the low control logic voltage and the transistor needs the higher voltage that does the work.

You could use a p-channel MOSFET but there really isn't any point for such a small motor.

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I've drawn what I was talking about so it's clear for you to see.

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Separate supply.GIF (3.1 KB, 42 views)

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Souper man

THANK YOU SO MUCH!!!

what is Rb?
a resistor of my choice?
Where does the + and - of the comparator go to? does - go to ground and + go to chip x?
Would i connect the negative termninals of both batteries to the negative bus?

 

Rb needs to allow enough current into the transistor to become saturated (fully turned on) so it can carry the current required by the motor. In order for this to happen the base current needs to be one tenth of the collector current.

Your motor takes 50mA so the base will require 5mA.

Suppose the battery's minimum voltage is 4.8V.

Here's how you calculate Rb:



The circuit illustrated in my previous post is not the complete circuit; it only illustrates how you connect the output transistor and motor to the comparator on the output stage of the first circuit I posted.

The complete schematic is the schematic in my previous post combined with the one in my first post. I suggest you read the website I linked so you can understand how comparators work before attempting to build this.

Yes, that's what I mean by a common 0V rail.

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Souper man

I still dont get it (sorry!), how is a comparator going to run this? the link doesnt even clear up my question. Could i use a H-bridge to run my motors?

 

You use H-bridge for direction control, but you don't need it right?
The comparator is used as oscillator, as PWM to control the speed of the motor. Am I right?

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