L298 Circuit problems HELP NEEDED

[olof102]

Hi,
I've built this circuit to power my DC motor in my robot. **broken link removed**

I use 3,3V logic output from my laptop (parallellport) but it doesn't work.

I'm also using BC548B transistors. Could those be the problem. When I apply high (1) to W1 and low (0) to W2 nothing happens.

 

[Vizier87]

why are you using 3.3 V?!!

 

[olof102]

The output voltage from my PC's parallellport is 3,3V. Won't that be enough?

 

[Dragon Tamer]

I though that the output from any computer port (except fire wire) was 5V logic.

 

[olof102]

Yeah, I thought so to until i recently measured and it said 3,3V.

 

[olof102]

Okey, I've now tried with 5V input instead, nothing happens. Could it be the transistors that are faulty?

 

[Vizier87]

at least use a 9V square battery for the supply, dude. It can show better results. 3.3V from laptop ports are for low-current applications. motors use much more power, and draws much more current.

 

[olof102]

I use a 12V 7Ah battery as Vcc to the IC. I've tried both 3,3V and 5V as logic Vs but neither works. I've also changed to 2N3904 transistors, still doesn't work! What could be wrong?

 

[atferrari]

Have you read the datasheet? What is the required voltage at Vcc?

What about the input signals to make it work? Guesswork is not reccomended. Why not to follow what is required?

 

[AlainB]

The 7805 need 2 small capacitors that are not shown in the schematic. See the datasheet. Using a buffer, maybe a 74HC14 betwen the port and the L298 would also help.