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  1. K

    Need help to understand circuit!!

    Based on what I'm seeing in the schematic, they're common cathode displays, not common anode. But for the purposes of answering your question that doesn't matter much. The micro is multiplexing the display by sequentially turning "on" each of the common cathodes via COM1-4 and displaying the...
  2. K

    Circuitry homework help please

    There's two ways to stop current flowing through a bulb. One way is by breaking the circuit to the bulb. The other way is... ??? hint #1: 5 letters starting with "S".... hint #2, no current flows through the bulb but current still flows somewhere.
  3. K

    Interrupt Do's and Don'ts

    Your way works but it's inefficient, in that when the interrupt is polling RCIF to wait for that 2nd byte, no other code is running. A better way is to use a state variable and an interrupt. When a byte comes in over the UART, the interrupt occurs and your interrupt service routine would...
  4. K

    Newbie Question - 1A at low voltage vs 1A at high voltage

    Power (watts) is a product of current and voltage. W = V * I. To use a water analogy, think of voltage as water pressure and current as volume of water over time, and a water wheel as a resistance (load). The water pressure and the volume (amount) of water passing over the wheel determines...
  5. K

    New to electronics, 555 help

    If the chip is getting hot, that means a lot of current is being drawn through it, possibly due to a short. Reversing the power supply can cause it as well. How hot does it get? Too hot to touch, or just warm? Try a process of elimination. Disconnect one part/wire at a time and see if the...
  6. K

    Whats the difference -volts and GND (0 volts)

    I don't see any schematic for a 555 circuit, just mentions of it. In any case, a 555 circuit won't need a split supply at all. If you just need a floating ground reference, say for an op-amp, you can use a voltage divider. Do you actually need a split supply for your robot? This...
  7. K

    Circuitry homework help please

    I'd start by drawing out a circuit for each of the given bulb combinations, leaving out the switches. Note that some bulbs need to be in series and some in parallel to get the indicated voltages. Then compare the resulting circuits and see where you would insert the switches to achieve the...
  8. K

    Whats the difference -volts and GND (0 volts)

    What supply voltage does the rest of your robot run on? What is that circuit supposed to do in your application? Looks like it just amplifies/buffers the voltage set by VR1, and VR2 biases the inverting input. If your robot has a single supply of say, 5V, use a rail-to-rail op-amp (the 741 is...
  9. K

    Neurodreamer that never worked

    Here's the datasheet for the CN3052A which is the regulator/charge controller for the battery pack: http://www.consonance-elec.com/pdf/datasheet/DSE-CN3052A.pdf For a power adapter, you need a 120V wall wart that puts out between 4.5 and 6V DC and has a plug that matches the size and polarity...
  10. K

    Motor bike lighting

    Use a voltage regulator. There are probably 6V ones for use on motorbikes/cycles out there. If you're using bare LEDs (rather than modules pre-wired for a certain voltage), you'll need to limit the current, either with a resistor or use a constant-current circuit. Have you measured the actual...
  11. K

    Puppy with light up fan

    Examine them to see if they appear to be in the correct spot and not bent. Worst case, you'd have to find a motor of the same size and spec (ideally the same motor) and replace it. At that point it might just be cheaper and easier to just replace the toy. When you say top part, do you mean the...
  12. K

    Lifting Electromagnet Solenoid Project

    A 12V lantern battery is typically around 7200 mAH (based on what I found on the internet). Your solenoid draws about 830 mA if the 10 watt rating is accurate. You'd get maybe 8 or 9 hours of on-time out of a lantern battery. If the gate is only going to be powered for a minute or so at a...
  13. K

    LED Confusion

    The Micropuck 2009A can drive up to 350 mA, while your LED is rated for up to 700 mA. When you drove the LED directly from the AAs, the internal resistance of the batteries likely kept the current below the 700mA maximum (so your LED didn't burn out), but higher than 350 mA. If you have a...
  14. K

    mosfet circuit?

    Have you measured the actual voltage of your PWM output? It should be higher than 0.6V, especially when you mention 5V PWM. It'll be alternating rapidly between 5V and 0V, with the duty cycle controlling the average voltage. Is this PWM output driving your gauge and a servo? What happens if...
  15. K

    Lifting Electromagnet Solenoid Project

    Looks like in your application it's an electromagnet, not a solenoid. But for the purposes of discussing the circuit that doesn't matter. What are you going to use to activate or deactivate the magnet? A switch? A button? A signal from something? That will largely dictate what kind of...
  16. K

    LED Confusion

    It's possible that the maglite isn't using a driver or series resistor, and just relying on the voltage drop of the LED (white LEDs usually are between 3 and 4V) along with the internal resistance of the batteries to keep the LED from blowing itself up. Perhaps you could take the flashlight...
  17. K

    using PORT A of 16f870

    Look in the datasheet for how to initialize the ADCON0 and ADCON1 registers. From there you should be able to figure it out.
  18. K

    When or where use EPROM and EEPROM?

    I don't think EPROMs are used much anymore, except in older devices that used them back in the day. For anything that needs to store data "on the fly", use an EEPROM. Most can be written to without requiring a high programming voltage, plus they can be erased and re-used without needing a UV...
  19. K

    Component questions (transistor, capacitor)

    You're right. That transistor has a 4.7k current limiting base resistor built in. As for the LED not extinguishing completely, what happens if you temporarily ground the base? Just to rule out some leakage current into the base causing the transistor to turn partially on. Either that or your...
  20. K

    Will this work?

    Got it. :) The datasheet doesn't say which pin is 1 and which is 3 on the actual switch, which is probably what led to your confusion when the LED wouldn't turn off. Just swap the connections on the two main pins and you're good to go.
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