Its not a good idea to make parallel port sink the base current of upper PNP transistor. If base current is too high, it may blow up the port. Also the voltage +V has direct effect on base, which when greater than 5V has potential to destroy the port.
So use additional NPN transistor to drive PNP. Drive this NPN with parallel port.
Its not a good idea to make parallel port sink the base current of upper PNP transistor. If base current is too high, it may blow up the port. Also the voltage +V has direct effect on base, which when greater than 5V has potential to destroy the port.
So use additional NPN transistor to drive PNP. Drive this NPN with parallel port.
The problem is not with the NPN transistor, its with the PNP. Ive built circuits with the parallel port using NPN transistors and they worked fine. A high output on a parallel port pin will turn an NPN transistor ON a low will turn it OFF. If you want to insure that the transistor is OFF ,during a low , simply connect a 10K or so resistor between the base and ground.
An even better idea when working with the parallel port is to use an opto isolator IC such as a 4N25 to drive the transistor. This will give perfect separation between the computer parallel port and any connected loads especially motors and relay.
I have a transformer that has three wires out: 0V , 6V and 12V
And i had a idea:
The uper shematicks can use a litle power suply changes!
V+ and V- can be the 6V on the transformer(with a diode to set polartivity)
The GND can be the 0V with the Ground on the parallel port
Can it work? :?
I know the motor will be a litle buzzy
PS:
I dont have a power suply like that so i will use a transformer!
The problem is not with the NPN transistor, its with the PNP. Ive built circuits with the parallel port using NPN transistors and they worked fine. A high output on a parallel port pin will turn an NPN transistor ON a low will turn it OFF.
Nettron, you can switch an NPN with the parallel port if the emitter is grounded. Look at the schematic. The emitter is connected to V-. If you ground the base, the base-emitter junction is still forward-biased. You need a PNP as a level translator.
I agree with your suggestion to use optoisolators for motor control.
Doh! hadnt noticed thats a dual polarity power supply.
But i'd caution against using PNP transistors on the parallel port. As Kinjalgp already mentioned the port would have to sink current to ground, ive bin warned by others , when i was working on my circuits , not to use PNP transistors.
Actually i later decided to go with a ULN2803 darlington transistor array IC to drive loads using the pararllel port.
Ive posted a schematic of my design in the Robotics chat forum of this board, if anyones interested.
Why don't you go in for L293 H-bridge ICs? You'll only require two of these ICs and each can deliver 1A current to the motor. And it has TTL compatible control inputs so you don't have to worry about interfacing it with the parallel port.
The top transistor will work as an emitter follower, so the voltage across the motor will never be more than the voltage on Data 1, minus the Vbe (0.7v) of that transistor. The bottom transistor will never switch the motor. What simulator are you using? Given your level of knowledge, I'd be more inclined to say it's a bug in the operator. :roll: I don't mean this as a put-down. It's just a fact that a simulator in the hands of an inexperienced person can give misleading results. In fact, a simulator in the hands of an experienced person can give misleading results, and the simulator is generally not the problem. I'm not putting down simulators - I spend most of my time at work using Hspice and Agilent ADS. I use Linear Technology's free SwitcherCAD III at home. This experience has led me to these conclusions.
Its a demo so i can't save circuit's but i am working a program to save the copy'd file from the clipboard and then paste it in agen!(Its Save/Load my stile 8) )