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  1. gorgon

    confusion over LED forward voltage rating

    For a blue LED I would think that 3.0V to 3.6V is correct. The typical value is between those margins. I would assume that the difference is just a printing error in the summary.
  2. gorgon

    i need help understanding this simple circuit

    Who say the voltage over the caps are constant? What is the voltage over C2? If you can find that, you're on the road to understanding. TOK ;)
  3. gorgon

    Need lower PWM frequency on Microchip PIC!

    It's a bit confusing. A duty cycle of 1ms, or 2ms, does not say anything about the PWM period. A duty cycle is normally in % of a a total period. The base input frequency of a PWM generator, together with the resolution of your duty cycle will give you the period and the frequency, or your...
  4. gorgon

    Where I can learn about 555 Astables.

    But, you'll also need the datasheet's technical specs of the part in question, to find if this is the correct chosen part in this particular design. So, we are in fact talking about several 'specs' in all cases of designing gizmos, of any kind. TOK ;)
  5. gorgon

    Where I can learn about 555 Astables.

    The specifications we talk about is the specifications for the end product, what you want to get out of your design. It is normal to setup the system specs when you design a new device or product. If you don't do that, how will you know how to design anything, or know that you are finished with...
  6. gorgon

    Where I can learn about 555 Astables.

    You need to define the specifications of what you want to get out of the design. Like the frequency and duty cycle for an oscillator. Then you look at the timing diagrams to get a ballpark value of the capacitor, for example. From that you can calculate the resistors, using the formulaes in the...
  7. gorgon

    Where I can learn about 555 Astables.

    Try to read the datasheet, there are application notes included. Like here: http://www.alldatasheet.com/view.jsp?Searchword=LM555 You need to select the datasheet to view it. NS normally has the best list of applications. TOK ;)
  8. gorgon

    How can I count analogue pulses over 10secs.

    To get a correct count, you need to get the time from the start-to-start, or end-to-end of the pulses. That's the period to convert to pulses/time unit. TOK ;)
  9. gorgon

    How can I count analogue pulses over 10secs.

    Make a Schmitt trigger based on a normal comparator, and you can set the trigger levels as you wish. TOK ;)
  10. gorgon

    How do I use a 7 segment LED display to show steps ie fan is speed 1,2,3...8,9 etc?

    Just a question. If I'm not totaly wrong, you count 2-4-6-8 in this example. Could it be that you have shifted one bit? TOK ;)
  11. gorgon

    How do I use a 7 segment LED display to show steps ie fan is speed 1,2,3...8,9 etc?

    With a 74xx147 you also need to generate a 5V supply for the logic chips. It is possible to get 4511 versions that work on 12v, without the need for an extra 5V. BTW if you add a quad comparator (like LM339) it is possible to sense the voltage directly without the extra transistors. TOK ;)
  12. gorgon

    How do I use a 7 segment LED display to show steps ie fan is speed 1,2,3...8,9 etc?

    Use one transistor for each voltage, and code the binary value with diodes. For this application the diodes could even drive the segments of the display directly, without the 4511 in between. You'll need a couple of diodes(5 really) more, but save the chip. TOK ;)
  13. gorgon

    Help with 74LS170 4x4 Register

    It is a standard warning in all TTL and LSTTL design books. The reason is the construction of the input transistors. If you hardwire the input to Vcc you will backfeed the input transistor and a corruption of the logic and increased power consumption may occur. If you look at the signal drawings...
  14. gorgon

    Help with 74LS170 4x4 Register

    Ok, Just had a look at the datasheet. You need to add pullup resistors on all the outputs, like 2k2. The outputs are open collector and will only pull to 0V, If you connect your LEDs via a resistor from Vcc to the output, you will see an inverted output. Light when '0' and off when '1'. TOK ;)
  15. gorgon

    Help with 74LS170 4x4 Register

    Sketch a schematic of how you have connected the chip, and explain in detail how you operate it. You say you connect LEDs, how do you do that? I suppose you know the outputs will sink more current than it will source? BTW You are sure the chip is in working order? TOK ;)
  16. gorgon

    Help with 74LS170 4x4 Register

    First of all, working with a LSTTL chip, never connect 5V directly to inputs. Always use a pullup of some kohms, like 2k2 or 4k7 to Vcc (5V). No problem connecting 0V directly. Try to change that and see if the chip starts working. When toggling inputs with a switch, I suppose you know that...
  17. gorgon

    Admiralty chart with LED sequences

    I was only asking to know the degree of realism in your display. Just curious. And yes, I meant that some lighthouses/marks display sectors/zones with different colours, maybe the smaller ones. You could make a cluster of small LEDs simulating a rotating lighthouse, but that might be...
  18. gorgon

    Using optoisolator as a switch

    If you measure between the input and the ground, you must have some form of voltage? The polarity of this voltage define how you connect a 'normal' optocoupler. The one you have described need Vcc on the output side to work properly, so you need to change the optocoupler selected, to a...
  19. gorgon

    uln2003 data sheet question.

    And you can't drive that contraption from a normal logic output. Each ULN driver need some current to work, the internal resistors draw between 1 and 2 mA at 5V input. With 14 inputs you'll need 15-30mA in total to activate the drivers. The max total power loss in each chip indicates a total...
  20. gorgon

    Choosing an IR photodiode or phototransistor for fire detection

    I know that the flame detector our company make, use a small low resolution camera chip to 'see' the flames. In addition to some heavy computing on the 'picture'. TOK ;)
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