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  1. BobK

    Small Microphone transmitter

    Not quite in the FM band though! I can get the oscillation up to 1MHz easily. It is when I try to get 100MHz that I have problems. I wish I could remember the circuit I used many years ago. I seem to remember needing an insanely low resistor (10Ω) as the load. Interestingly, I saw an ~100Mz...
  2. BobK

    connect optical audio speakers to tv with no optical audio

    Gryd3, It is not surround sound, just two speakers and a subwoofer. The RCA jacks should work fine for input. Thuhobbit, Does you TV have RCA audio out jacks? If so, just connect them to the jacks on the interface box. Bob
  3. BobK

    Microcontroller Motor control help

    Look up H-bridge. This is a circuit that allows you to reverse polarity to a motor. It requires 4 switches, (MOSFETs or BJTs), If the motor is running off the same voltage as the microntroller, all you need is 2 P-channel and 2 N-channel MOSFETS. You can also buy chips for this purpose. The...
  4. BobK

    connect optical audio speakers to tv with no optical audio

    Are you sure it only takes an optical connection? This info from Amazon indicates otherwise: And the picture of the interface box shows a white and red RCA jack, standard for line level audio input. Bob
  5. BobK

    Problem with 5v power supply

    7V at 1.5A is 10.5W. I don't think that heatsink is sufficient. At full load it is going to be very hot. Bob
  6. BobK

    Project 1 : Battery pack / charger

    9V and 1.5W is .167A nor mA. That is 167mA. And a boost converter raises voltage and lowers current, a buck converter lowers voltage and (possibly) raises current. Both lose a little in the process. From the microchip site: So 167mA is within it's range. But I should also ask if you...
  7. BobK

    Capacitors in parallel effects on frequency

    Say you connect a 1M resistor to the + terminal of a 1V battery. What is the voltage between the other end of the resistor and the - terminal? How about a 1K resistor? A 1Ω resistor? Answer to all: 1V. You need two resistors to make a voltage divider. An RC filter is voltage divider in...
  8. BobK

    Stage Line 500W amp repair project

    Getting a low reading from B to E or C is okay. Do these readings again with the diode check range on your multimeter. They should read about 0.6V. If you get a reading with the black lead on the B, it is a PNP, with a read lead on the B is an NPN. You should have 2 of each. Bob
  9. BobK

    Peltier device for cooling beer keg

    I don't know exactly how much cooling you will get, but my gut feeling is that you will be disappointed. Bob
  10. BobK

    Peltier device for cooling beer keg

    10A might not be enough for both of them since they are claimed to use up to 72W which is 6A each. Also, I hate to tell you this, but two of those are unlikely to cool a keg of beer or even keep it cold. Bob
  11. BobK

    Low voltage Relays

    Use a transistor to either switch the load or switch a relay for higher loads. This might help: https://www.electronicspoint.com/resources/using-a-bipolar-transistor-to-turn-a-load-on-and-off.30/ Bob
  12. BobK

    Switching loads using Raspberry Pi

    An interesting question is why nearly every beginner seems to come up with the emitter follower configuration when first trying to use a BJT as a switch. My guess is that they have a notion that a switch is something that switches the power on an off, and therefore it should be between the +...
  13. BobK

    Advice on USB-powered LED Lamp circuit

    Why is there any capacitor there at all? It should be unnecessary unless it is really a 1F, which I doubt, and is intended to keep the light on after unplugged from USB. Bob
  14. BobK

    PIC Compilers

    I would try de-installing and re-installing then. Bob
  15. BobK

    Renewable Energy (part 2)

    Or you could use a boost converter if you get less than 12V from the turbine. Bob
  16. BobK

    PIC Compilers

    Are you using MPLAB or MPLAB X? I am not sure the XC compilers work with MPLAB. Bob
  17. BobK

    PIC16F877A With GSM Modem SIM900A

    If I read the datasheet correctly, that module wants TTL levels, not RS232. You should remove the MAX232 from the circuit. Bob
  18. BobK

    Small Microphone transmitter

    I have tried the circuit (2nd one) from the "Spy Tools" link on a breadboard and it does not oscillate, though it will with higher inductors and capacitors. On LTSPICE it seems to work, so perhaps the problem is with stray capacitance on the breadboard. Bob
  19. BobK

    PIC Compilers

    There are also 4 families of PICs with different instruction sets. There is not one compiler that handles all of them. I use the XC compilers from Microchip, which are free (with optimization disabled.) There are 3 of these to handle the 8, 16 and 32 bit PICs. Bob
  20. BobK

    I need to power my Halloween costume

    I would suggest that any method of powering 120V XMAS lights on one's body would be dangerous. Please consider using low voltage strings of lights, which are available. We have some that run off 4 AA batteries, and they lasted quite well, getting 10 hours or more out of them. Bob
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