Prototype Circuits

Prototyping improvements







  • Cheap multi LED bulbs are best for backlight as are bright, ie 5 led corn cob type throw more light sideways which is best IMHO
  • BUT Cheap LED bulbs are polarised, ie no inbuilt rectifier so..
    • only fire on half the cycle:
      • so in NZ 50 HZ mains =some flicker at lower brightness levels
      • I see some wierdness where different bulbs on the same string work differently, (but in these circumstances polarity is random)
      • only on for half the AC cycle
Potential solution:
  • a simple AC-DC rectifier with a few smoothing caps to help with the flicker
    • ~6.3v in  = about 9V out - loss through rectifier but on for longer..
  • will just use thru hole parts I have on hand and put it together on stripboard
  • Rectifier diodes, I have IN4004 & Schottky as well IN4008? both 1A or thereabouts from memory.  Will use the Schottky first for less voltage drop
  • The largest cheap caps I have are 40uF 16v electocaps
  • With the Triac's drivng the GI circuits, on the lower brightness, the 'on time' of the AC must be proportionally fairly short, so we have a high proportion of 'off time' per AC cycle, which leads me to think about a resistor in series with the smooting cap to help further with the flicker..
    • Possibly a couple of caps with varying RC..
    • Might have to bread board the caps part and try a few variations..
Something like this
Ok, working for some brightness but not 4-6, either off or random flashing.  This is driving a string of just LEDs.  SO substitute 1 incandesant and we get mostly a better result.  So.. hit the book.. and a Triac needs a resistive load to turn on.. Hmm how much load?
One reason to move to Leds is to reduce power usage & also current flowing through the Pinball electronics...
So will put a resistor across the AC supply to provide a load.  Whats on hand.. ok so I have ~900R 1/8W resistors which will be safe enough at 6.3v AC
No, much varying and sometimes slow flickering, caps are making no difference