DC motor timer controller

[Ipanema]

motor timer controller

hi,

I need to design a 3V dc motor controller. Here how the operation should be :

push toggle (start) ==> motor turn for 3 minutes ==> stop or;

==> push toggle (stop)


only one push button toggle for start-stop function and also a battery low indicator.


Pls help.

Thanks,
Ipanema

 

[IanP]

You can do it using two completely different approaches:
First, standard circuits, 555 chip as the 3min timer plus some CMOS or TTL gates to realize the logic, or second, employ a small microcontroller, such as PIC, and reduce hardware to minimum.
The advantage of the latter is that you can change the way your circuit will be functioning just by software means, but the choice is yours..
Regards,
IanP

 

[Ipanema]

Hi Ian,

Thanks for your suggestion.

I've figured out how to implement the delay functions in PIC and now I would like the DC motor to have constant speed, which won't vary with battery voltage variation / battery life. Two battery will be use, hence 3V supply. Pls suggest how to do this with minimal components, better if can be implemented with single PIC.

Do you guys have any suggestion of cheaper PIC than PIC10F2XX and PIC12F50X for this application?

It would be much appreciated if you can point me to any sites that have similar design.

Thanks and best regards,
Ipanema

 

[IanP]

Rotation control, or constant RPM, will require a shaft encoder, and these devices are not cheap. Maybe in your application you can implement a good ( 90% and more efficient ) switchmode voltage regulator which will give you moretheless stabile rotation control.
Regards,
IanP

 

[Ipanema]

Hi Ian,

Thanks for your suggestion. But in my application, I can't afford more IC due to very low budget of the design. Do you have any cheaper discreet solution to this? I'm thinking of using zener diode as a voltage reference. What do you think of this?

Regards,
Ipanema

 

[IanP]

You can use zener diode, but better solution would be to employ any voltage regulator. If you can't use a switchmode IC then maybe you will consider very popular and not expensive (probably will cost you the same as a zener diode) linear adjustable regulator such as LM317(L): **broken link removed**
It looks like small, 3-leg transistor, and on top of everythng has current limit of 100mA (just in case) ..
Regards,
IanP

 

[Ipanema]

Hi IanP,

With low supply voltage at 3V, the dropout voltage of LM317L is already 2V. I think it won't work. :-( Any solution?

I have measured the operating current of 3V DC motor, which is 150mA.

Thanks and best regards,
Lee

 

[IanP]

I have forgotten that the supply source will be 2*1.5V batteries. In this case the "317L" is totaly wrong option ...
On the other hand, if you can't go for a small high-efficient switchmode alternative, zener diode, if used, will just drain batteries. I can not see any simple "linear" solution ..
Other option is to go for good batteries (same as used in digital cameras) and they will maintain almost contant voltage for a reasonable perioid of time ..
Regards,
IanP