View Full Version : very basic question about motors

11-02-2004, 10:02 PM
hi all.
I was just going through the article available in this forum.It stated that DC motors run from 1.7V + so on.
So now take a DC Motor that runs with 3V.Earlier too i asked this question about the Parallel Port.What is the output voltage for boolean '1' on a parallel port pin??suppose that its more than 3V then my question is will the 3V DC Motor Run straight away when i connect one wire to 1(3V) and othee wire to 0(ground).Logically speaking it should work.Vikas also gave that we must use the H-bridge.But is it necessary in this case?
Well do DC Motors really cost just few tens of rupees???
Bhargav :lol:

11-02-2004, 10:55 PM
Hi ,

well .. here are ur answers ..

1)parallel port output .. is +5V when its boolean 1 and 0v when its boolean zero.
2) U can't drive a motor directly .. as current delivered by a parallel port is of very less magnitude. U have to use a interface circuit. like H bridge or simple BJT ...
3) you can get a 6v motor ( used in tape recorders .. 2400 rpm ) for rs. 30 /- or more .. depending on its quality

I hope this helps :)

MIG India

11-04-2004, 06:42 PM
well simply said the parallel post does not deliver enough current ... that is why an external powersupply is needed to drive motors ( On its own it can barely switch a LED )

11-05-2004, 02:40 PM
First of all we must consider both the voltage level as well as the current capacity. The voltage level may be adequate but the current sourcing capacity (the maximum current it can provide to the load connected to it) of the computer parallel port is of the order of 10-15 mA. Even a small DC motor may need current of the order of 500mA to run. Thus connecting a DC motor to the port directly may damage the port circuitry of the motherboard.

To drive motors, the most simple circuit could be a NPN BJT with the port feeding the base of the transistor and the motor between the +ve external supply & the collector. connect a diode in reverse bias parallel to the motor to filter out the transients generated by the motor. The transistor amplifies the current going in it's base, which is actually sourced from the external power supply. This circuit ofcourse is the simplest but is highly inefficient.

A much better solution is using an H-Bridge (search google for the circuit diagram), alternately you may get an H-Bridge IC such as L293D, which is adequate to run small tape DC motors. The H-Bridge allows you to have on/off as well as direction control.

Good Luck !

01-16-2005, 11:29 AM
U can also use relays for having the large currents which may not be fulfilled by using BJT .this is just an independent circuit with a electromagnet which causes closing of above circuit when current flows through it.

02-26-2005, 06:08 PM
have u red ibm parallel port definition

parallel port can source 1mA and sink 20mA

You know that this is not enough to drive motor

you use one power transistor b/w them

03-09-2005, 11:42 AM
:!: Please check the datasheet of the DC motor, the parallel port available on PC is for transmitting TTL signals for external devices, not for driving motors which require heavy current source. more over when motor stops it produces lot of back emf which may produce sparks and so be careful. you have use a H-bridge for that and control the speed of by PWM, which has inbuild mechanism for protection

03-10-2005, 03:00 PM
have u red ibm parallel port definition

parallel port can source 1mA and sink 20mA

You know that this is not enough to drive motor

you use one power transistor b/w them

I have got a query related to parallel port access. I am using linux on my machine. I am learning driver writing for Linux. so that I can drive desired bits on the ports. But learning driver writing has become too cumbersome task.

I believe you must have driven your PCB by your computer somtime in your design setup. Can you share with me the expertise and skill set required to build such a system? Any directed or indirected solution would serve the purpose.

Though "RealTime Workshop" (A Matlab Toolbox) can easily do the job, I want to do it by writing my own C program. So please help.

I shall appreciate references too.


07-31-2006, 02:38 PM
Well evryone has said enuf bout it ...

i just wanna add this .. dc motor costs few tens of rupees .. a parallel port or maybe a mother board dosent ..
y take a chance .. use ur parallel port for switching purpose rather than drivin loads from them