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  1. AnalogKid

    Detecting an active low signal

    If you can modify the wire harness to tie the spare pin to either a Vcc or GND pin already on the connector, then it still can be used. If not, then can you post a pinout list of all of the pins and signals so we can see what we have to work with? Also, what is the connector type? ak
  2. AnalogKid

    Detecting an active low signal

    I'm saying that if there are two unused pins in the connector, you can use one pin on the PIC to sense when the connectors are mated, independent of any other signals on the connector. If the connector does not have two free pins, then we move on to another technique. ak
  3. AnalogKid

    Detecting an active low signal

    If you are talking about detecting a physical disconnect from the pc board connector, one of the easiest things to do is jumper together two of the removable connector pins. At the mating pc board connector, connect one pin to Vcc through a pull up resistor and to the PIC pin, and the other pin...
  4. AnalogKid

    Pre-Scaling a squarewave. Output weird.

    I don't see any triggering on a rising edge. Also, the output trace now is not at all distorted. It is ok for the chip to drive multiple LEDs as long as you keep the currents very low. For a 5 V circuit and 2 V LEDs (a very common Vf value), place a 2.7K to 3.3K resistor in series with each...
  5. AnalogKid

    Circuit to switch off a DC motor

    Hitting 90 degrees with nothing but a timer means it will have to have an adjustment so it can be tuned. Is this the sequence: Everything off Switch closes > timer starts > motor runs > gate opens > timer stops > motor stops > gate is held in open position Wait Switch opens > timer starts >...
  6. AnalogKid

    Circuit to switch off a DC motor

    Your question has very little information. Are you talking about the motor in the train, or the motor that operates the gate? Are there a sensors on the gate to indicate when it is fully open and fully closed? What voltage? What current? What tells the gate when to open? ak
  7. AnalogKid

    Pre-Scaling a squarewave. Output weird.

    The schematic does not show the LEDs, and the protoboard image does not show how they are powered. Is the common connection to all LEDs Vcc or GND? Also, do you have a scope shot of any output when *all* LEDs are disconnected? ak
  8. AnalogKid

    Pre-Scaling a squarewave. Output weird.

    A common issue with small wall wart power supplies is that they need a minimum load current to stabilize the magnetics and make a clean, low impedance output. This can have all kinds of strange effects on circuits. If you have a 47 ohm 1 W resistor, add it to the circuit directly across the 5...
  9. AnalogKid

    Pre-Scaling a squarewave. Output weird.

    Without a schematic or scope photos or a photo of the construction, I have nothing to look at, either. Scope photos? Grounding scheme? Construction photo? Length of the ground lead on the scope probe? Perf board? Solderless proto-board? Power supply decoupling? Schematic? ak
  10. AnalogKid

    Current passing for regulator IC's

    You didn't do us the courtesy of including the datasheet for the part you are using, so this is only guesswork. Assuming your part is similar to the standard LM7812, using a PNP pass transistor will get you additional output current while limiting the current through the regulator, plus...
  11. AnalogKid

    led pulse / breathe light board

    The LM358 is a dual opamp, almost certainly configured as a comparator with hysteresis to form a square wave oscillator. Depending on the exact circuit, it is entirely possible that changing the value of the pot has no effect on the adjustment range. In this case, some other resistor on the...
  12. AnalogKid

    led pulse / breathe light board

    Schematic? The photo is so fuzzy it contains very little information: What are *all* of the markings on the chip? Can you post a more clear photo? Can you post a clear photo of the bottom side of the board? You said you want a 3 second pulse, but you didn't say what the pulse time is now - ...
  13. AnalogKid

    Multi Meter usage

    If you are saying that this cable comes from a power supply, like a small plastic box that plugs into a wall outlet, the plug on the end of the cable does not look correct for that. As above, post a photo of whatever the cable comes from. ak
  14. AnalogKid

    DIY voltage Regulator

    What you have is not an LDO, either in circuit configuration or in performance. According to your numbers, you need a minimum 18.5 V input to maintain a 12.3 V output. That is a minimum dropout voltage of 5.2 V, about twice as much as with an LM317 or 7812. A true LDO would have a minimum...
  15. AnalogKid

    Volts per metre

    Think about a rubber band stretched until it is 1 m long. The tension between the endpoints is 1 band per meter. Now pull two identical rubber bands; that pulling force is 2 bands per meter. Note that this analogy does not travel well. Stretching 1 band to 2 meters doubles the force, while...
  16. AnalogKid

    Old Style Op Amp

    Ya know, I just gonna let that one slide...
  17. AnalogKid

    Old Style Op Amp

    Which dressing would you like with that word salad? W.h.a.t. in the world are you talking about? ak
  18. AnalogKid

    Power supply !!

    I've been puttering around with a power supply schematic based on an LM358. It is CV-CC, regulates down to zero volts and zero amps, and does *not* require a negative bias voltage. The target is hobbiest quality - the regulation down at the low extremes would not be great, and probably would...
  19. AnalogKid

    Power supply !!

    It's in the original schematic. ak
  20. AnalogKid

    Power supply !!

    None of those circuits will adjust down to 0 V output, or have adjustable current limiting. ak
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