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  1. Herschel Peeler

    8051 power supply

    Is your 8051 already programmed? Is there more writing on it than a date code and part number? As far as a programmer goes the 8051 is pretty old. You may have a problem finding one that runs on a USB port. You can spend big bucks and buy a general purpose programmer (best if you can afford...
  2. Herschel Peeler

    Driving a 10 watt LED

    I can only give general responses to vague descriptions. I need part numbers of some kind to get specific. Generally, yes, you need current limiting. That being said, I have a high Watt LED designed for 12 V that I have been running just fine as a desk light for almost a year now. No current...
  3. Herschel Peeler

    Voltage Drop across NPN BJT C&E?

    You are correct, of course, but can you change voltage without changing current? I draw a specific current through the base to get a certain voltage. With the same base voltage and current can I have different collector conditions? I cannot calculate collector voltage knowing base voltage, or...
  4. Herschel Peeler

    Voltage Drop across NPN BJT C&E?

    Is it a question of EITHER base current OR base voltage? We can't change one without changing the other. It is convenient to find gain using base and collector currents. But it is easier to explain a current mirror by looking at base voltages. Both are important. Under some specific base voltage...
  5. Herschel Peeler

    "random" blinking LEDs: purpose-built circuit, or Arduino or =

    Yes to three circuits but I doubt if they would be synchronized. Or you could adjust the timing resistor a little on each circuit to be certain. You could use a pot as the timing resistor and make it variable. R2 a 1 M pot.
  6. Herschel Peeler

    Mini Camera/LED/Power supply research project

    Re: 6 V It looks like there are four more batteries on the other side. Re: resistor for the LED. About 1,000 ohms. (500 to 2,000) Just wire the LED and resistor in parallel with the camera.
  7. Herschel Peeler

    How do constant current loads work and how to make one

    Something like this? Basically you use a transistor as the load. You turn it on and into conduction just enough to be the resistance you need. Instead of driving the load it is the load.
  8. Herschel Peeler

    How do constant current loads work and how to make one

    More specifics, please. Vague assistance is all we can give for vague requests. What schematics have you found so far that might be close to your needs?
  9. Herschel Peeler

    "random" blinking LEDs: purpose-built circuit, or Arduino or =

    How about 10 LEDs that each blink for about 200 ms. About 80 seconds to run a complete cycle. I use the high side current limiter of the TTL circuits to limit the LED current. I haven't tried this yet with white or UV LEDs.
  10. Herschel Peeler

    "random" blinking LEDs: purpose-built circuit, or Arduino or =

    Here is an LED flasher that blinks the LED for a fraction of a second every 8 seconds or so. With 30 LEDs in the system how many did you want on at any given time? This circuit blinks on for about 200 ms. No current limiting is used on the LED so it drives all out for that 200 ms. I used a white...
  11. Herschel Peeler

    Switching leds

    What is OP1 like? Is it a typical IR LED in the optoisolator? I would expect about 1.2 V across it and 0.6 V across the diode, making the business end of R14 around 2 Volts at about 2 mA (??!!). With TR1 on it would be even less.
  12. Herschel Peeler

    Trying to make a transistor cancel another transistor

    A lot simpler than mine. Can you do it with PNP's like he wanted?
  13. Herschel Peeler

    Trying to make a transistor cancel another transistor

    One section like the three transistors on each LED section. Lots of parts ... or an LM3914 which is designed to do what you want lighting one LED at a time.
  14. Herschel Peeler

    Trying to make a transistor cancel another transistor

    Agree. This is a learning experience for him.
  15. Herschel Peeler

    Trying to make a transistor cancel another transistor

    What temperature range were you interested in monitoring? How much does your sensor change per degree? Do you hae a part number we can look up?
  16. Herschel Peeler

    Trying to make a transistor cancel another transistor

    Attached is a next step. Eight LEDs, 4 blue, 4 red, each turned on individually, On one section two transistors are added (Q9, Q10, R17, R18, R19) are shown. R17 and R18 are a voltage divider. When the voltage applied to R19 reaches the voltage at the voltage divider plus about 0.6 V Q9 turns...
  17. Herschel Peeler

    Trying to make a transistor cancel another transistor

    Ah, I see. Now that is something different. Lots of parts or an IC, LM3914.
  18. Herschel Peeler

    Trying to make a transistor cancel another transistor

    Okay, first step forward. Four red and four blue LEDs running at 4.5 V from batteries. The size of the resistor determines the current through the LED. Running from batteries you may not want to drive the LEDs at 20 mA or 30 mA. This is one option of what the LED and driver might look like. More...
  19. Herschel Peeler

    Trying to make a transistor cancel another transistor

    Super. Take it one step at a time. Four red LEDs and four blue LEDs. What voltage are you going to run it at? That will determine how they will be wired.
  20. Herschel Peeler

    Trying to make a transistor cancel another transistor

    So many simpler possibilities if you don't want to use so many transistors, but I assumed there was a learning experience in this.
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