controlparallel port
simulate this circuit – Schematic created using CircuitLab
Parallel port ideally gives TTL logic 0(low) and 5V (high). But my port gives 3.3V high. I have designed my controlcircuit assuming the high to be 5V? Is there a way to regulate the 3.3V to 5.0V so that I can still use the existing control circuit?
thanks in advance
There are plenty of ways, Here's two: -
Note the diode across the motor - this is needed to protect the BJT (or MOSFET) when the transistor is switched-off - this circuit will be OK for low-power fans. Rate the transistor in accordance with the current the fan needs.
Or...
This circuit will run from 5V or a lot higher should your fan be (say) 24V or 12V. Not shown is the reverse connected diode which you must have.
Pick a P-channel MOSFET with low "Vgs(threshold)" to ensure it turns on properly
The basic "Centronics" printer port protocol uses a simple 2-wire handshake in which the PC asserts a strobe signal until the printer asserts an acknowledge signal. This repeats for each byte transferred.
If you want to "bit-bang" individual pins on the parallel port, you can't use the Windows printer drivers; you need to access the hardware at a lower level. If you're using a USB-to-parallel converter, you'll have to read its documentation.
Best Answer
TTL logic should accept anything over 2.0 volts as a high. A TTL output high is only guaranteed to be above 2.4 volts, according to an ancient TI databook.
You shoud therefore design your inputs to accept anything over 2.0 volts as high, and anything under 0.8 volts as low.