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  1. KrisBlueNZ

    Transistor Uses

    When a BJT is used as a switch, it is always in one of two states: OFF and ON. Just like a light switch. A BJT is controlled by its base. Applying a voltage between the base and emitter causes current to flow, and this makes the transistor conduct. It allows current to flow through its...
  2. KrisBlueNZ

    Strange problem with transistors flipping current

    I don't see a schematic... Also can you post a photo of your construction.
  3. KrisBlueNZ

    LDR with two LEDs

    Hi Joe and welcome to Electronics Point :-) Yes, you can use one LDR to control two LEDs, but you haven't explained how you want to control the LEDs based on the light level at the LDR. Do you have a description you could post? Do you have a schematic (circuit diagram) of what you have been...
  4. KrisBlueNZ

    A little help on how to switch transistors

    It depends on what collector current you will be running the transistor at. But all but one of those lines is measured at VCE = 10V which is not true when you're using the transistor as a saturated switch. This is why you should use a base current several times the value you calculate by...
  5. KrisBlueNZ

    Can i Send gps (nmea) data down a AUX plug?

    Hi Ryan and welcome to Electronics Point :-) NMEA data is normally asynchronous serial at 4800 bps. Is that right? So you want to send async serial data down a cable that's designed for audio? What distance? What type of cable? Is it shielded? Do you know the capacitance per unit length from...
  6. KrisBlueNZ

    Impedance measure circuit ?

    Do you mean impedance, or just resistance? If you mean impedance, you have to specify at least the test frequency. If you mean resistance, the usual way is to supply a known current and measure the voltage drop that it produces. Is this the kind of answer you're looking for? If not, explain...
  7. KrisBlueNZ

    A single pulse on power-on?

    OK, sorry about the delay! Here's my suggestion. The circuit is based around U1, an LM393 dual comparator. This IC contains two comparator circuits, each of which compares the voltages at its inputs and drives its output accordingly - it pulls its output down to 0V if the voltage on its...
  8. KrisBlueNZ

    Help Selecting A Switch (Novice)

    I suspect Hop's idea is better but here's what I had in mind using the Digi-Key part I linked in post #2. The two wires on the right go to the positive sides of the LED strips and the negative sides of the LED strips are returned to chassis.
  9. KrisBlueNZ

    NAD CD Player front panel buttons dead!

    I get no hits for Komex soldering station. I don't know whether the iron operates at mains voltage or whether the tip is earthed. It's possible you've damaged the components that scan the tact switch array. Have you checked every track in the tact switch area for continuity? Can you post a...
  10. KrisBlueNZ

    Kenwood Receiver KR-A4070 Issue

    Great! That was lucky!
  11. KrisBlueNZ

    Help Selecting A Switch (Novice)

    Hi there and welcome to Electronics Point :-) A rotary switch is probably your best option - they're easy to mount, and they're available with various numbers of positions. They're not the cheapest switches available though. Slide switches are available but they are harder to mount in a panel...
  12. KrisBlueNZ

    NAD CD Player front panel buttons dead!

    Start by carefully checking the work you did replacing the tact buttons. Make sure you didn't accidentally break a track, or dislodge a connector, or forget to reconnect something you disconnected. Did you use any electrostatic precautions when you replaced the tact buttons? Is your soldering...
  13. KrisBlueNZ

    Problem with Interrupts - PIC18F1220

    The RBIE bit is in INTCON, along with RBIF. Now you have the code working, how about changing it so the LED flash interval is controlled by a variable, and having the interrupt handler modify the variable somehow. The variable should be declared volatile.
  14. KrisBlueNZ

    Amps higher than voltage possible?

    I thought it would be helpful to show some examples of components and circuits, along with their V-I graphs, so I simulated four of them using LTSpice. Here is the schematic: The "RAMP" generator at the left generates a linear voltage ramp from 0V to +10V over the simulation period of 10...
  15. KrisBlueNZ

    Problem with Interrupts - PIC18F1220

    Ah, the analog input "feature" that's ON by default. I remember making a mental note to watch out for that. Then obviously, I forgot! Good catch Bob.
  16. KrisBlueNZ

    Hold 5v Line

    RT determines the delay, in conjunction with CT. Specifically, the delay is proportional to RT × CT. You can vary either of them to change the delay, but RT should be kept around that value. RP is only needed to protect the gate input from damage when the circuit is turned OFF and CT is still...
  17. KrisBlueNZ

    Amps higher than voltage possible?

    Yeah, I wasn't going to!
  18. KrisBlueNZ

    Hold 5v Line

    Oops sorry, I didn't read the first post carefully enough. Both edges need to be delayed. On power-up the output will be high for about eight seconds, because CT will initially be discharged. If that's wrong, move CT so its positive plate is connected to VCC and its negative plate is...
  19. KrisBlueNZ

    Hold 5v Line

    Here's a simple way to do it. When the input goes high, pin 2 goes low, and D1 conducts, charging CT so its negative side sits at around +0.7V. The output will be high. When the input goes low, pin 2 goes high but CT does not discharge throgh D1; it discharges through RT. Pin 3 will reach...
  20. KrisBlueNZ

    Amps higher than voltage possible?

    No, that is not generally true, and making that assumption will mislead you. Voltage and current are only proportional to each other in an ohmic component. Resistors are ohmic, but most of the components you will encounter, and almost all of the circuits and subcircuits you will encounter, are...
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