Re: Mini version of Scophony - its do-able
Posted: Mon Dec 28, 2020 7:14 am
Scan circuits for line and frame
This is what I used originally which worked for the line scan well, but was unfinished for the frame scan. Both Line and Frame use the same circuit, but with different timing values.
Basically the 4046 operates as a VCO using the internal analogue comparator 1, which compares the signal from the mirror sensor with the incoming sync signal. The 2 mono-stables ensure the mark to space ratio is 50:50 (optimized for 60 lines but less for 32 lines) which the analogue comparator works best at.The output voltage of the comparator varies accordingly and controls the VCO thus synchronizing this to the incoming sync signal. The VCO centre frequency is set to the normal clock frequency required to drive the stepper motor. Q4, R13,R22, and C12 are use to provide the slow ramp up which the stepper motor requires. This probably will not be required for the frame scan as the stepping rate is far lower.
For 32 lines format
Line scan motor speed for 15 sided mirror = 60*32*12.5/15 = 1600 RPM
Frame scan motor speed for 8 sided mirror =60*12.5/8 = 83.75 RPM
For 60 line format
Line scan motor speed 1600*60/32 = 3000 RPM
Frame scan motor speed = 83.75 RPM
This is what I used originally which worked for the line scan well, but was unfinished for the frame scan. Both Line and Frame use the same circuit, but with different timing values.
Basically the 4046 operates as a VCO using the internal analogue comparator 1, which compares the signal from the mirror sensor with the incoming sync signal. The 2 mono-stables ensure the mark to space ratio is 50:50 (optimized for 60 lines but less for 32 lines) which the analogue comparator works best at.The output voltage of the comparator varies accordingly and controls the VCO thus synchronizing this to the incoming sync signal. The VCO centre frequency is set to the normal clock frequency required to drive the stepper motor. Q4, R13,R22, and C12 are use to provide the slow ramp up which the stepper motor requires. This probably will not be required for the frame scan as the stepping rate is far lower.
For 32 lines format
Line scan motor speed for 15 sided mirror = 60*32*12.5/15 = 1600 RPM
Frame scan motor speed for 8 sided mirror =60*12.5/8 = 83.75 RPM
For 60 line format
Line scan motor speed 1600*60/32 = 3000 RPM
Frame scan motor speed = 83.75 RPM