I am trying to develop a RGB conversion for a technics 1210 turntable. The platter strobe is giving me a bit of trouble when I use neopixel.
I measured the original led strobes and I saw a 101 hz cycle with 1610 micro seconds off and 8200 micro seconds on period. I was able to reproduce the strobe using a simple led, but I have struggled to reproduce with a neopixel using the original lib and the fastled lib. The problem is I cant turn them off quick enough to match the 1610 micro seconds needed, the lowest I could get was 4000 (watching the data with my scope) and that is too long.
If I am using a set number of leds could the software be optimised just for this one use ?
I would guess that you cant also with APA102 or SK9822 because they have a built-in / fixed (although faster than Neopixels…) PWM control of the brightness.
I think you need to go regular RGB LEDS for your purpose.
I brought a few sk9822 and APA102C . To get a normal RGB led working I would need to use PWM to adjust the colours levels, but then I would need to switch on and off to match the speed of the platter strobe light and the original has 4 leds so I would also need a transistor of some sort to power all 4 from the same PWM signal. would you agree ? I also thought about the fact that I switch them on at the start and then off at the end of the loop, would the end of a cycle add a very small amount of time to the off period ?
@marmil I will look at that example using fastled and a normal rgb 5050 and see if I can tweak that to work. I just need 2 or 4 to work in the strobe and they will all change at the same time so I would control from one output and use something to power via a transistor.
@marmil I have it working with a normal 5050 rgb, but it’s strange the dots on the platter are inverse to the original. The background is more prominent than the dots, but the dots do move as they should when the speed is changed. So now I need to get 4 working at the same time.
Edit, I reversed the timing so it’s on for the short period and off for the long, I guess this matches the spacing of the dots and gap.
@marmil I guess I added the edit after your comment, but yes my on and off was reversed. I would need to send a video to show it working and will do once I have a few bits working.
I managed to fit a 5050 rgb led into the space of the original strobe LEDS but they are set quite far back compared to the old ones and only one is working at the moment. I think using 5mm rgb led would be closer to the original. I also have this working with timer one so the led is flashed at the correct speed all the time.
If you decide to use addressable RGB LEDs, make sure to use APA102Cs since they have a higher PWM rate. Now, the concept with strobing is to have an ON time and OFF time with a 10-90 duty cycle ratio. For example, a 1ms period (equating to 100 Hz) would keep the LEDs on 10% of the time and off the remaining 90% of the time. Higher ON times create a ghosting effect while lower ON times create a sharper image at the expense of brightness. 5050 RGB LEDs work OK too but the downside is that the whole strip ends up being the same color since they aren’t individually addressable. Using individually addressable RGB LEDs opens up a whole world of effects that look quite visually impossible.
@Stephen_Co In this case the strobe needs to match the spacing of the dots on the turntable at two speeds. I used my scope to measure the original strobe and then changed my software to match that 1950 - 7880 Us for 33 and 1460 - 5900 for 45. I do have some apa102c on order so I will still give them a try, but I did find a physical issue with how the pcb fits inside. The 5mm leds are mounted quote far away from the pcb to clear a brass fitting that the on off knob fits into so using smd actually has clearance problems at that point. I was thinking I could make a new pcb mounted away from the original to give the space it needs.