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  1. BobK

    transistor pain

    Agree with jackorocko about using an NPN, but you need to connect it differently. The emitter of the NPN should be connected to ground, the collector to one motor lead and the other motor lead to +9V. Bob
  2. BobK

    speech recognition project

    Microchip actually has speech recognition software for the dsPIC chips, so it is quite possible. Interfacing a microphone is done through an opamp preamp that amplifies it and offsets it by 1/2 Vdd then using the built in ADC. Bob
  3. BobK

    change the range of a battery using a varistor

    Also, the voltage you read will depend on load, and is not a good indicator of battery life left since it does not go down linearly. The correct way to do a battery fuel gauge is to integrate the power drawn from the battery, and the charge put into to. There are ICs that will do this. Bob
  4. BobK

    DIY PCB

    How did you end up doing it? Bob
  5. BobK

    How does my Ikea lamp work?

    11.5V will not electrocute you. You cannot measure the current by clipping onto the two leads. You have to break one of them and put the meter in series with it. I am sure you would read 1 or more amps that way. Bob
  6. BobK

    switching voltages

    Well, that depends a lot on what you are doing with the voltage. How much current will be drawn? Bob
  7. BobK

    HELP! (PIC16F84A Digital Clock)

    He is using a 3 1/2 digit display since the fourth digit can only be a 1. It could be easily modified to use 4 full digits. Bob
  8. BobK

    HELP! (PIC16F84A Digital Clock)

    Here, for instance, is one with a PIC16f628, you could use a PIC16f628A which is a more recent PIC that is more powerful and costs 1/2 of what a PIC16f84A costs. http://www.bowdenshobbycircuits.info/pic_ck.htm Bob
  9. BobK

    HELP! (PIC16F84A Digital Clock)

    Why does it have to be a PIC16F84A, which is an obsolete PIC? Bob
  10. BobK

    PIC Type

    If you need only 1 analog input and 1 digital output, there are 6 pin PICs that can do this! Look at pic10f220 for instance. Bob
  11. BobK

    Mosfet driver, do I need it?

    Are you talking about an electomechanical switch? Switching times for MOSFETs are not really problematical at low frequencies. It is only a problem if the switching time is a significant percentage of the duty cycle, which means the MOSFET is in the linear region a lot of the time and...
  12. BobK

    1 volt signal

    Uh, no. Try this: Ib = Ic / Hfe = 0.017 / 440 = 0.000038 Vrb = Vin - Vbe = 1.0 - 0.7 = 0.3 Vrb = Ib Rb Rb = (Vrb / Ib = 0.3 / 0.000038 = 7894 The first eq. states that the current from B to E is is the desired collector current divided by the current gain. The second eq. states that...
  13. BobK

    MIT offers free undergraduate level electronics course

    :rolleyes: Bob
  14. BobK

    How do drive a power mosfet gate

    The driver should be push-pull. If it is not, that is why your MOSFET is staying on. Have you looked at it with a scope? Bob
  15. BobK

    How do drive a power mosfet gate

    twister, You do not understand power MOSFETs. The gate is basically a capacitor. In order to switch it quickly, you need to charge / discharge this capacitor quickly, which means lots of current. Typical gate drivers can source and sink 1 A for the hundreds of nanoseconds that it needs to...
  16. BobK

    Speed controller for valves

    Use a 555 timer. Here is a lot of info on them. There is plenty more on the net. https://www.electronicspoint.com/timers-notes-less-experienced-work-progress-t220141.html Boib
  17. BobK

    Digital Electronics

    I am not sure what you are thinking here. The clock will change (depending on the logic you use) either on the rising edge or the falling edge of the 1 Hz square wave. The change will appear instant to human eyes. Bob
  18. BobK

    How do drive a power mosfet gate

    This is for a boost converter right? If so, do not put a diode across the coil to suppress the voltage spike, that spike is your high voltage output! Bob
  19. BobK

    digital logic design

    7 half adders. Assuming you don't need carry in to the first bit. Bob
  20. BobK

    What is the output voltage in this circuit?

    Well you see it wrong then. If the sine wave source is ideal, it as as Duke says, it forces the voltage to be the that of the sine wave. If the sine wave source has an internal resistance, then the same current must flow though both the resistors and the voltage will be a sine wave with an...
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