Search results

Search Forums New Posts
  1. AnalogKid

    Pulse dropping circuit.

    Will this design track the input signal without adjustment as its frequency changes over a 10:1 range? ak
  2. AnalogKid

    Pulse dropping circuit.

    "deliver the remaining pulses as an output at the input voltage" "the pulse voltage is current" I'm struggling with your language, but I think this is it: You have a continuous pulse train that is the tach signal in a car engine, and you want to reduce the signal to 2/3 of it's original...
  3. AnalogKid

    400ma bipolar 12v 2 ohm drain

    Without some kind of context, I have no idea what you are talking about. When you say "drain", are you talking about the drain pin of a FET or MOSFET? What is a "2 ohm drain"? If you are observing 400 mAdc passing through a 2 ohm resistor, the voltage across the resistor will be 0.8 V. What...
  4. AnalogKid

    LM358 Replacement

    Maybe it isn't the part, but the way it is being applied. ak
  5. AnalogKid

    LM358 Replacement

    There are thousands of dual opamps with the same pinout; it is an (unwritten) international standard. As above, there is much more to an acceptable substitute than just the pinout. The LM358 has input, output, and power characteristics that are *not* standard, and neither of the two parts you...
  6. AnalogKid

    LM358 Replacement

    The 358 is rated for operation down to 0C only. The far right column is for the LM2904. ak
  7. AnalogKid

    LM358 Replacement

  8. AnalogKid

    LM358 Replacement

    Or LM2904 (same data sheet). ak
  9. AnalogKid

    Convert 12V to 3V Without affecting Total Resistance

    As above, it depends on what the 0-12 V is coming from and what the 0-3 V output is connected to. Without those two pieces of information, calculating a 2-resistor voltage divider is guesswork. You can use a high impedance buffer like an opamp voltage follower to isolate loading effects, but...
  10. AnalogKid

    Parallel port - control pins

    If you are using the FETs as analog switches that are charging a capacitor to a positive voltage (above GND), you need to change to p-channel devices. ak
  11. AnalogKid

    Parallel port - control pins

    The schematic has several problems. The BS170 is shown operating as a source-follower. This means the minimum voltage drop across the device is its threshold voltage, approx. 2.1 V. What is tye purpose of the capacitor at the input the the LM324? It will need some kind of resistor or...
  12. AnalogKid

    555 timer output clipped

    If I understand things correctly, the problem is that a 555 powered by 8 V doesn't produce an output that peaks at 8 V. This is correct operation for the bipolar NE555, and is shown in the datasheet. Changing to a CMOS 555 (LMC555) will improve the output, but it still will not be perfect...
  13. AnalogKid

    Parallel port - control pins

    2.3 V is a bit low, but still acceptable as a signal level on a parallel port pin. For some low voltage and low power applications, you can use combined signal pins to power a small circuit. Your project needs too much power for that, so you will need a separate 5 V power supply for your...
  14. AnalogKid

    Switches

    A 4PDT (four pole double throw) switch will do this. But for either this or using gates, you need to define what states you want the four inputs the inverters are driving to see when the inverters are disconnected. You cannot just let the inputs float; they need to have a defined state, high...
  15. AnalogKid

    Convert 12V to 3V Without affecting Total Resistance

    The "Converted Out" divider is connected to the wiper. If the input to RV1 has a zero ohm source impedance, the maximum source impedance for the output divider is 250 ohms. This can be used to calculate how much "Output" sags under load. ak
  16. AnalogKid

    Convert 12V to 3V Without affecting Total Resistance

    It is hard to answer questions with missing important information. What are the values of R3 and R4? You might have a problem satisfying two conflicting requirements. If you increase R3 and R4 both by 100x, then they will not load the output of the pot as much. But, the converted out source...
  17. AnalogKid

    Electronic Dice Timer Circuit

    For the display, yours has cathode connections on pins 4 and 12, while the schematic shows a single connection on pin 3. Obviously the schematic is based on a different part, so check all of the other pin assignments carefully. Attached is an actual datasheet for the 7448. As noted on page 1...
  18. AnalogKid

    Electronic Dice Timer Circuit

    Are you sure you are using a common cathode display? Also, not all displays have identical pinouts. Can you post the datasheet for the one you are using? ak
  19. AnalogKid

    SMD 0805 capacitors

    It sounds like you are trying to repair an SMT board for which you have no schematic, BOM, layout information, or reference designators. Not a good starting point. Do you have any information about the product? Can you post photos? ak
  20. AnalogKid

    Electronic Dice Timer Circuit

    7448 pins 3, 4, and 5 are not shown on the schematic. This is a serious error. Pin 4 can be ignored, but pins 3 and 5 must be connected correctly or the part will not drive the display. The datasheet has a table that shows the connections. Also, this part will not drive the display directly...
Top