Amanita Posted October 9, 2010 Report Share Posted October 9, 2010 As there are only 8 LED dropping resistors on the control pcb, are the LEDs multiplexed at high frequency? Can't fit ohms law into it otherwise... I want to use my own LEDs and understand that I will need to trial a few resistances to get the intensity right so I intended to just set up a 5vdc psu and breadboard until happy - then fit. But only 8 resistors and 48 LEDs which come on in different quantities.....enlighten me please....:) Quote Link to comment Share on other sites More sharing options...
Flemming Posted October 9, 2010 Report Share Posted October 9, 2010 I am very sure that you are right, 8 resistors for all the LEDs on SammichSID! MB6582 has over 100 LEDs (64x LEDs for modulation matrix, 48x other CS LEDs on control surface, 1x LED for power on) and it has only 16 Resistors for all of them. Thank Wilba for the lovely LED-matrix voodoo which makes this possible :) Quote Link to comment Share on other sites More sharing options...
Wilba Posted October 9, 2010 Report Share Posted October 9, 2010 The LEDs on sammichSID are multiplexed... they are in an 8x6 LED matrix, but driven by the PIC using the default MIDIbox SID 8x8 LED matrix code, so in reality they are really in a 1/8th duty cycle. In my experience, if you are testing what resistor will work, testing one LED with constant 5V will be about the same brightness as when it is in the matrix, it won't be much less bright when put in the matrix. It depends on the LED type, though. But as a rule, it's OK to pick a resistor using constant 5V as a test. Alternately, solder the LEDs before soldering the resistors, run the sammichSID CS test app (I really should put this somewhere better): and then touch resistors in the pads to see actual brightness. You could in theory put all 8 resistors in the pads (without soldering) and trim/bend the leads to make good contact. As a general rule, ultrabright LEDs (especially white or blue) will need at least 1K resistors... perhaps even as much as 3K. Quote Link to comment Share on other sites More sharing options...
Wilba Posted October 9, 2010 Report Share Posted October 9, 2010 Also... you can get your 5V DC for testing from the sammichSID itself... use J2 in the bottom right corner on the base PCB, or even J2 on the control surface PCB (Vd=5V, Vs=ground). Quote Link to comment Share on other sites More sharing options...
Amanita Posted October 10, 2010 Author Report Share Posted October 10, 2010 Cheers guys. A Quote Link to comment Share on other sites More sharing options...
Amanita Posted October 10, 2010 Author Report Share Posted October 10, 2010 Sooooo after testing - 220 Ohms it is then....... :whistle: Quote Link to comment Share on other sites More sharing options...
Wilba Posted October 10, 2010 Report Share Posted October 10, 2010 LOL BTW If you're not happy with the red LEDs in your kit, you can send them back for a full refund ($3). Quote Link to comment Share on other sites More sharing options...
Amanita Posted October 11, 2010 Author Report Share Posted October 11, 2010 Hehe they're on the way - a bankers draft will do... TBH - i never really intended to build with red leds so i'm not sure why i ordered the kit with them. Still, i have the pcbs for a MB6582 knocking about so maybe they have a useful future. A Quote Link to comment Share on other sites More sharing options...
Wilba Posted October 12, 2010 Report Share Posted October 12, 2010 Sorry, can't send bankers draft overseas... it will have to be via Western Union. :D Quote Link to comment Share on other sites More sharing options...
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