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Gregory wrote:Thanks Gary for all the info, very useful. One question - with the xtal oscillator how would you get the frame or line beginning to coincide with the actual spot position or in other words the black frame band to be at the bottom of the screen and the line black band on the left - I assume this may have to be done manually?
Steve Anderson wrote:I have to say that driving a stepper motor of the common variety at 8kHz is likely to be a disappointment. At least marginal. Please prove me wrong.
Gregory wrote:Steve Anderson wrote:I have to say that driving a stepper motor of the common variety at 8kHz is likely to be a disappointment. At least marginal. Please prove me wrong.
Hi Steve - The 8 khz refers to the steps the driver is receiving, The stepper driver has a micro-steps feature which basically divides the full step into smaller steps (ie this produces the sine wave drive required using PWM) I have set the dil switches to divide by 16 micro-steps, which is the smoothest selection available, so one full step is divided into 16 smaller steps, and so the actual stepper motor receives 8khz/16 = 500 full steps per second.
The resolution of the motor I am using is 200 full steps per rev so I am getting a speed of 2.5 revs per second and with my 8 sided frame scan mirror this gives me the 20 frames per second I need. I have found the motor runs smoothly on this speed, but to start it I still need to start form a lower frequency and ramp up.
Harry Dalek wrote:Hi Gregory
You have a horizontal display not that it matters just turn its side for Baird scanning .
gary wrote:60 lines at 20 fps and 4:3 aspect ratio (you don't seem to have explicitly defined the aspect ratio but you have mentioned a 6cm x 8cm screen so I assume 4:3)
SR = 20 x 60 x 60 x 4 / 3 = 96000 (BW of 48kHz)
Theoretically modern sound cards can handle 192kHz sampling (96kHz BW).
I have never been able to get around to testing that the output filters of such a sound card pass that BW though, as, of course, the human ear can't hear anything above around 20kHz, so it remains to be seen if the manufacturers do or don't take advantage of that to relax the filter response requirements.
I can provide you with the necessary software to produce the signal if you wish to experiment.
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