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  1. BobK

    Wanted: Commission for circuit and/or PCB design

    Here, I will save you a lot of money. You don't need a PCB. This is better wired point to point. S1 is a DPDT switch. S2 and S3 are the limit switches. These need to be momentary contact level switches that are normally closed. M is the motor. It's operation is simple. When S1 is one...
  2. BobK

    Will this synthesizer work?

    For a synthesizer, you really don’t want sine waves. They sound absollutely boring, not like any instrument because they have no harmonics. A softened square wave, i.e. with a low pass filter to round the edges, sounds vaguely like a woodwind. A sawtooth sounds vaguely like a bowed string...
  3. BobK

    Create controlled 50v pulse

    Why are you messing with PWM to generate single pulses? All you need to do is turn the pin on, delay the required time, then turn it off. At 16 MHz, an instruction time is 250 ns, so, with no delay you can create a 250ns pulse, and with delays, any multiple of that. Bob
  4. BobK

    Will this synthesizer work?

    Because it shorts the power supply. You cannot get a 50% duty cycle with the standard astable circuit. Connect the pot to the output pin to get a 50% duty cycle. Bob
  5. BobK

    Will this synthesizer work?

    You cannot connect the discharge pin to Vcc, this is a short when discharge is low. There may be other problems. And, no, you cannot drive a speaker directly from an op amp. You need an audio power amp. Bob
  6. BobK

    Create controlled 50v pulse

    55 MHz is not that high. A 2N3904 is 300 MHz. Edit: Which does not mean that it can switch that fast. Saturation switching is much slower, probably in the range of 1-10 MHz. Transition frequency is where the gain goes to 1. Bob
  7. BobK

    Create controlled 50v pulse

    You circuit will not switch in microsecond time because the combination of the 1K resistor and the gate capacitance will cause too long a rise time. It will turn off fast, but not on. The circuit Steve posted uses two BJTs: one to pull the gate low and the other to pull the gate high. This...
  8. BobK

    Question on reversing polarity for DC Motors

    See post #10. You need a switch on each end of travel that is mechanically triggered by the moving part. The switches are wired in series with the power supply so that when either of them is pressed the power is cut off. Bob
  9. BobK

    Is MW LRS 100-24 a good power supply? + possible leakage solution question

    What kind of leakage are you talking about? And it almost certainly has a cap across the power outputs, pretty much all DC supplies do. Why is this a concern to you? There will be a large AC component if you remove the capacitor. Bob
  10. BobK

    Question on reversing polarity for DC Motors

    What you want is limit switches. Switches that activate when the object reaches the desired position. Then all you need is a DPDT switch for direction and 2 normally closed limit switches. When the object gets to the desired position, the corresponding switch is hit and the motor is cut off...
  11. BobK

    Frustration over IR transmitter and receiver how do I..?

    TSOP receivers are very finicky about the signal they receive. It must be at the specified frequency ± a few percent. It must also be modulated. If you produce a steady 38KHz, it will initially recognize it, then ignore it. You must produce bursts of a specific range of length followed by...
  12. BobK

    PIC18F4550 interface display is not working on power ON

    Your code makes little sense to me. What is it trying to do? Here is what it appears to do: if the low 3 bits of PORTB are all 1, we are done, return. wait 20 msec. if the low 3 bits of PORTB are all 1 we are done, return. set LATB to 0x1F (four low bits on, all others off) if the low 3 bits...
  13. BobK

    Need help finding power source for solenoid

    No info about duty cycle. Bob
  14. BobK

    Need help finding power source for solenoid

    Can you link to the solenoid? Push- pull indicates to me that one pulse pulls it in and the next one releases it. It sounds like you are powering it continuously, which might not be allowed and explains why it would overheat. Bob
  15. BobK

    Green 532nm DPSS laser pointer...

    An LM317 has a dropout of about 2V, but why are you asking that if the module has a current regulator built in? What you need to know is what range of voltages the module operates at. Bob
  16. BobK

    Once a minute chirp...

    Since this is exactly what a 555 does, you just need to duplicate it. But why? Bob
  17. BobK

    need help to find alternative IC

    You will get up to 1A if you have a proper heatsink. Bob
  18. BobK

    Movement sensor

    The light pressure from the LED will not slow it down.:) Bob
  19. BobK

    Movement sensor

    An LED and a phototransistor would be my choice. IR if the light would be visible through the window and you don't want that. If I understand the geometry of this thing, the LED / phototransistor would see the coin edge on, maybe as little as 1 mm. In this case, the detector will probably...
  20. BobK

    Movement sensor

    I might not understand the problem correctly, because this sounds absolutely trivial to me. All you need is an LED and some form of photodetector placed such that the falling coin interrupts the light from the LED to the detector. Am I missing something? Bob
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