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Harry Dalek wrote:Great work at 12 ! i would been lucky to work out lighting a light globe at that age .\
I like the reed switch idea closest i have used is hall effect sensor ic and magnet yes most go down the optical road less mass to deal with .
Disk is pretty good for a home made too.
For DC-restore use the simple one transistor BUZ11 circuit from the NBTV Handbook. Although that circuit looks te be too simple, it works well and does DC-restore by a simple small diode. More over that circuit has inhaerent gamma correction, which gives a better rendering of grey scales. The pictures that you showed are only black and white, but you will soon go to natural pictures with shades of grey.
For the banding it is the disc that gives this. However I have seen it worse. Making an almost perfect disc is very difficult. I advice you to be proud on what you have done. Only a computer drilled or punched disc is slightly better.
I also can advice you to find yellow or amber LEDs for the light box. Our eyes are more sensitive to the more yellow light than to the red light.
Andrew Davie wrote:Trying to recall how this was all calculated, but given 4 LEDs in series, then about 2.2V/LED that would make 8.8V drop across the string. You don't have a 12V supply you say, but don't mention the voltage you do have. But going with 12V for my calculations, the resistor is "adjusting" 12V-8.8V = 3.2V and with a 150 Ohm resistor, 3.2/150 --> 0.021 (i.e, 20mA give or take) which sounds just about right for LED current. I don't see how 22 ohms would have worked at all. Hmmm. If the voltage was much lower it wouldn't be able to light a string of 4 LEDs. So, what IS your voltage?
Klaas Robers wrote:I think 150 ohm will do.
- A current of 20 mA through 150 ohm is 3 volt.
- 4 LEDs in series is indeed 8.2 volt, say 9 volt.
- Then LEDs and resistor = 12 volt.
- from your 19 volt remains 7 volt for over the transistor. That seems to be enough.
The resistors are only to distribute the current of the transistor evenly over the 3 strings.
Your observation of a better grey scale rendering is the effect of the right gamma of the circuit. Gamma is a non linearity in the light output that compensates for the non linear sensitivity of our eyes.
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