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  1. BobK

    why we use ports ?

    You apparently misunderstand what ports are. They are pins that you can either control or read from the microcontroller. Of course you connect external signals to a microprocessor pin. That pin is either an input or an output pin to the microcontroller. What else would you connect it to, a...
  2. BobK

    Add DC offset to AC signal

    If do it without an op amp, you will probably need an op amp buffer in input or output or both anyway. A passive circuit will have low input impedance and high output impedance. Bob
  3. BobK

    Watchdog Timers

    Please explain what you mean be a software watchdog timer. I think this is a contradiction of terms. A watchdog timer is used to catch runaway software by making certain that the software checks in within a settable interval. You cannot do this with software. Once the software goes into a...
  4. BobK

    Simple Circuit Problem

    Adam, What he wants is when in state 1 the two switcheson the left control the lamps, and when in state 2 the two switches on the right control them. As is, if both switches are on on either side, the lamps cannot be controlled independently. IMHO, diodes in series with each switch is a fine...
  5. BobK

    Which transistor to choose for my regulators !!!

    Converting down from 24V to 5V with any but very small currents is a bad idea. Get a 5V USB charger to power your 5V electronics. Bob
  6. BobK

    Resistances of different lamps

    It will give the resistance at whatever voltage it is using to test it. That will not be the same as the resistance when the bulb is operated at it's rated voltage. Bob
  7. BobK

    How to best simply invert a 110v ac current w/minimum change to the voltage

    I still have no clue what you are trying to do, and you questions are nonsense. Please describe what you are trying to achieve rather that ask up about a part of what you think the solution is. Bob
  8. BobK

    Electric Calculations

    We still need the current of the LED at 3.6V in order to calculate the resistor. Bob
  9. BobK

    Home made speaker

    You are definitely getting there. A couple of comments, though. If you use two diodes to replace R2, it will improve the circuit. And this is a current amplifier with no voltage amplification. Depending on the characteristics of your speaker, that may or may not be the right thing. Bob
  10. BobK

    How to increase current in a circuit

    If we could boost both voltage and current at the same time, we could run everything off a button battery! Bob
  11. BobK

    Playing a car audio system at home.

    I had a TV that I rescued from street side on large trash day hung on a chains over my bed. I repaired it by bringing the tubes to Radio Shack for testing. Bob
  12. BobK

    Best Way To Mount High Voltage Circuit

    48V and 2A are not high voltage or current. Normal construction techniques are fine. Bob
  13. BobK

    How to boost Ardrino Output

    That works fine if you only need to sink current. Bob
  14. BobK

    How to boost Ardrino Output

    You need a half-bridge circuit. Two MOSFETs (one N-channel, one P-channel) will do it, if properly chosen. They must be fully on at 5V and pass negligible current at 2.5V to avoid shoot-through. Bob
  15. BobK

    Op Amp not working properly LM324

    Okay, it helps when you tell us what you are trying to do. What you want is a ±2.5V signal with a 2.5V DC offset. This gives you a range of 0 to 5V. Run your input through a capacitor, followed by 10K resistors to ground and 5V. Connect this to your + input. Change the gain to 10. And use...
  16. BobK

    Op Amp not working properly LM324

    What are you trying to drive with this? An LM324 will not drive a speaker. Bob
  17. BobK

    Question about current sources - Not getting the correct current through load

    Most likely, it is the 0.6V you are using for Vbe. This is a reasonable typical value, but is not accurate at all. Vbe will vary quite a bit with base current. Bob
  18. BobK

    Controlling 2 servos at the same time?

    Well, you can get a 20ms period, but you have to run the processor at 893KHz. ànd then, the resolution for the duty cycle is 1 part in 50,which might be enough. I prefer not to waste 96% of the processing power to get a 5 bit PWM. Bob
  19. BobK

    Controlling 2 servos at the same time?

    Actually, the PWM modules are not good for controlling servos because the frequency is too low. An interrupt driven software PWM works better. Bob
  20. BobK

    Converting a Sync on Green signal to VGA/HDMI or anything 720p+ capable

    What you need is a composite video to HDMI converter. Bob
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