View Full Version : one simple question :)

12-02-2004, 01:59 AM
I have just assembled a toy car with four motors.
its working fine. now i want to control it using my pc.
right now, i am using two DPDTs (ON - OFF -ON) -one for left pair of motors n one for right pair. each pair has three states which are independent of states of the other pair- forward, reverse and off.

I am able to send high/low signial at desired parallel port pins,
now to drive the motors, i suppose i'll have to use a relay switches.
i'm using four 12V 3A motors. Please tell me the specifications of the relay switch i should use so that i can supply power to these motors
upto their maximum rated limit. note that the two motors on same side are connected in parallel. and they rotate in same direction at all times.

12-02-2004, 12:41 PM
Hi check out this article


hope it answers your questions ... If it dosent let know ...

12-03-2004, 01:38 AM
I had been thru that article.
I tried using 6V SPDT and 5V DPDT, but these relays didn't change their states when I changed output at the parallel port .
My parallel port gives abt 4.8 V for high n 0.2 V for low.
I connected the relay to a variable source (1.5 - 12 V, 3A) and found that it switched only at a higher voltage
is their any solution?
are there relays available that switch at abt 2V 10mA , or at still lower values?
here I would like to ask whether current supplied to the relay matters or its just the voltage that does?

Pls let me know the different parameters of a relay . I need the exact specifications of the relay that I should use.

PS: After a lot of experimentation, the port is now giving just 3.1 V for high o/p. I probably need an even more sensitive relay.

12-03-2004, 11:49 AM

There are relays that look like IC chips. Dont know there specifications. These are made to work in very low voltages. (very sensitive)

For relays both current and voltages matter.

Recommended way of interfacing devices to pc ports:

If I were in your situation, I would have used a optocoupler circuit. (Google optocoupler+parallelport+circuit) with 12v relay.


12-03-2004, 01:35 PM
Good idea shiraz, i think optocouplers can do the job right away.....try "MCT2E", a widely available optocoupler.

These take less current to drive them, and can drive power transistors, which in turn would drive the relay, motor etc.

This also helps isolate the parallel port circuit from the relays, thus ensuring safety of the PC I/O card.

12-08-2004, 03:14 PM
Thanks Sumandeep,Shiraz and Vikas.
I used MCT2E. its too good.
I can now operate the car thru keyboard.
Which source is typically used to produce logic 1 at an input pin?
Is there any standard device available to produce just enough power?

12-08-2004, 04:06 PM
logic 1 is equal to 5v ? its the powesupply ... whats your question to be exact .

12-10-2004, 01:41 AM
i'm trying to give input to parallel port using 7805 regulator IC. the o/p of this IC is about 4.6 V 22mA which I think is insufficient for being considered logic 1. when i increased supply voltage to the IC, it became very hot n started giving 1.2 A o/p which is too large. what should i do. is there any specific IC that i can use for this purpose?

Gurumurthy Arkasali
06-23-2005, 11:27 AM
Hi I am connecting Relay of 24V 6A to microcontroller through Optocoupler.

Relay is 24V trigger. Please help me by providing the corresponding circuit


Gurumurthy Arkasali

09-22-2005, 06:37 PM
how can i make an opto-coupler using a transistor(2SA1015)?

09-22-2005, 06:45 PM
how can i make an opto-coupler using a transistor(2SA1015)?the circuit should act like an opto-coupler.

12-18-2005, 02:58 AM
i made one using ir receiver transmitter leds....
it workd gr8...
u can try tat to...
better than a transistor...