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  1. gorgon

    If the source voltage is the same as LED voltage, is a resistor necessary?

    One thing you should be aware of is that the LEDs Vf has a negative temperture coefficient. The higher the temperature, the lower the Vf. If you have no current limitation in your design, you may get a current runaway situation, if for some reason, the temperature in the LED is raised. If your...
  2. gorgon

    7 Segment Display Filter

    Depends on the transparency, but why not try it?
  3. gorgon

    7 Segment Display Filter

    If you use all colours in the same display, you need to use a colourless filter with just a slightly reduced transparency. I would start with a smoke coloured filter with 30% light reduction. This will increase the contrast of the display.
  4. gorgon

    Hi everyone

    Welcome to the forum, Steve.
  5. gorgon

    Multitasking an Arduino

    One trick when you use an interrupt timer routine, is to use a counter instead of a single flag. That way you will know if your state machine is executing too slow, and you will always run the correct number of timer ticks.
  6. gorgon

    Trouble with tribbles.. erm, timers.

    Yes I see that now, I took it for granted that PNP transistors were used as row drivers. The reason was the loss of voltage headroom for the LEDs, using emitter followers. Sorry about that.
  7. gorgon

    Trouble with tribbles.. erm, timers.

    It is not that easy to calculate the resistor, when using relative weak microcontroller outputs, since the output voltage from the microcontroller will fall when loaded, You really need to look into the datasheet, and see the max current output available. This will normally be when the output...
  8. gorgon

    Trouble with tribbles.. erm, timers.

    You are in fact shorting the outputs from the microcontroller to 'gnd' vs '+5V'. This is the same for both the NPN and PNP transistors. You'll overdrive the microcontroller outputs, with way too much current, and may as Steve say damage the outputs. One thing that is certain is that the outputs...
  9. gorgon

    LED Screen

    One thing that may not be a problem here, but can be in other constructions, is the reverse voltage breakdown limit of 5V for most LEDs. Depending on the driver types, and voltage for driving LEDs in the matrix, this may ruin the LEDs if you apply more than 5V reverse on them. If the drivers on...
  10. gorgon

    Trouble with tribbles.. erm, timers.

    You should add some base resistors on all the transistors. The way you do it draw a lot of extra current and strain both the driver outputs and the transistors. You also ovedrive the transistors and that may be the reason for you ghosting. Use 2k2 for the NPN, and 4k7 for the PNP. It could even...
  11. gorgon

    Looking for a component marked "made in Austria"

    Hopefully it was in good order, and not crashed? Looking forward to see what you manage to do with it. ;)
  12. gorgon

    Basic LED help please!

    I hope you are aware that 1A is absolute max current for continuous use. There should be a safety margin when using a resistor for current control.
  13. gorgon

    Really small motors

    Is this a kind of art display, with a moving picture? Is there any load on the pins? what are the direction of the pins, horisontal or vertical? Can the movement be in steps? 100,000 pins sounds like a major installation.
  14. gorgon

    Display cabinet - PIR motion sensor & LED lights

    It is a LED - Light Emitting Diode we talk about, not a resistor? And the OP measured it to 3.2V @13mA
  15. gorgon

    Display cabinet - PIR motion sensor & LED lights

    A single normal LED will not jump around like that, if you have 3.2V @ 13mA, you will not have 3.8V @ 20mA. The 3.2 - 3.8V is the range that you can get the Vf in for the LEDs as a group, not as a single LED. The max Vf you will see for the 3.2V unit will be around 3.3V close to max current, if...
  16. gorgon

    Display cabinet - PIR motion sensor & LED lights

    As long as he measure 3.2V over the LED, there is no reason he can't get 20mA through it, IF the available voltage is present. The problem has to be the total available voltage. Is the 6V supply 6V? How much does the transistor drop? With 80mA for 6 LEDs, the average current is 13.33mA that is...
  17. gorgon

    Display cabinet - PIR motion sensor & LED lights

    The normal Vce voltage drop over a single transistor will be in the order of 0.2- 0.4V, and this is easy to measure. I would think that using 120 ohm resistors will bring you closer to the goal of 20mA, depending on how the Vf is reacting to a greater current. How much more light you get remains...
  18. gorgon

    Trouble with tribbles.. erm, timers.

    What are the current values you are using on the different components in your matrix? Can you draw one column driver and one row driver chematics, with all the component types and values? I suppose all drivers of each type is equal? Regarding the ghosting, as long as it is trailing, you need to...
  19. gorgon

    Trouble with tribbles.. erm, timers.

    As long as you don't change the row and column data synchronous, you need to turn off the column driver before you change row data. To do this without setting the column driver signal to hi-z, you could add a gate after the register output, to make it possible to activly drive the driver signal...
  20. gorgon

    Trouble with tribbles.. erm, timers.

    The ghosting problem is one of the reasons you should complete each column with all 20 values before changing to the next column. If you don't do it already. Pulldown resistors is essential to turn off the column drive transistor.
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