search on "parallel port rc servo controller" lots of hits, but I didn't go look at them. Basically, even if you use a serial and or a parallel port, you typically have a microcontroller chip perform the actual RC servo controlling. Serial is more practical which is why you see them in use. I think you need to provide some more details, like how many RC servos you need to contol, how much resolution do you need (such as 256 steps versus
1024 steps), and so on.
For one RC servo, you could use a microcontroller that has 8 digital input lines, with one RC servo signal output line. Then if you set the 8 inputs to a bnary 127 you have a center position on the servo, 0 gives full throw one way, 255 gives you a full throw the other way. Anything in between move the servo that amount proportionally.
There are web sites that have info on programming your own PIC to control servos, but I have not been successful in doing this yet. You can control 3 more of these 555 based controllers by using the parallel port control pins 1, 16, and 17 (15 is already used) to clock/latch the 3 new controllers. The data pins to the 4 controllers would be in parallel from the parallel port. You could also use two 74HCT259 chips controlled from the 4 control pins to individually clock up to 15 of the 555 controllers (I use this as a webcam switcher). You might also be able to just to use transistors to switch on/off the +5V power to the individual servos if they don't have sufficent load to rotate them off position when power is removed. Haven't tried that yet. Some links below.
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