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  1. KrisBlueNZ

    NPN circuit not behaving...

    You say the CE pin voltage is 0V before the button is pressed, and 3.3V when the MCU has latched it ON. So what is the CE pin voltage when VUSB is present? That circuit is very straightforward and can be diagnosed step-by-step pretty easily. You understand how it works, because you designed it...
  2. KrisBlueNZ

    Need help with a Power Failure Alarm Circuit

    The graph shows the voltage on the "0V" rail relative to the Neutral rail for a capacitor-fed bridge with the capacitor in the Phase line. I was just pointing out that the "0V" rail of the circuitry does not go far from the Neutral voltage. So although the "0V" rail is not grounded, and must...
  3. KrisBlueNZ

    conundrum, please help with circuit, new to forum, probably easy fix for some

    Yes, there are several ways to do what you want. I would probably use ICs from the "4000 CMOS" series, which can operate from any power supply voltage in the range 3~15V. (Other types of logic ICs, such as TTL, are fussy about their power supply voltage.) The details, such as which IC to use...
  4. KrisBlueNZ

    NPN circuit not behaving...

    Your circuit should work OK. What type of transistor are you using for Q1? What is the voltage on U3 pin 3 in each state? What is the minimum threshold voltage specification for U3 pin 3?
  5. KrisBlueNZ

    Need help with a Power Failure Alarm Circuit

    All agreed Chris. Although, if you're using the capacitive reactance feed method and you put the capacitor in the phase line before the bridge, the circuit common (which is the best way IMO), the circuit common (negative bridge terminal) doesn't sit half way between Phase and Neutral (on...
  6. KrisBlueNZ

    Need help with a Power Failure Alarm Circuit

    As well as being dangerous, your circuit won't work properly. 1. R6 will form a voltage divider with R5 which will prevent U1E's output from reliably holding U1D's input high. I suggest you remove R6 completely. 2. The polarities of the SET and RESET signals for the latch are both the same...
  7. KrisBlueNZ

    Clairon car stereo

    Good advice, dh390.
  8. KrisBlueNZ

    NiMh batteries problem

    Oh sorry. I had the idea that your batteries were D size. Probably because of the high claimed capacity figure. But they're AAs. I guess they could be AAA internally, but there's little reason to do that, because the cost difference between AAAs and AAs is not much compared to the cost...
  9. KrisBlueNZ

    FOG MACHINE PCB FAULTY

    Good work! That is the full schematic, before all the important information was removed. I can now see that it is not very well designed! Can you make some voltage measurements on the main microcontroller U7. The 0V reference for the black multimeter probe is the GND rail, which is the tab of...
  10. KrisBlueNZ

    Car phone connector to powerpoint

    Many modern phones use MicroUSB connectors can be charged from a USB connector. Is that what you want? If so, you will need a regulator to drop the automotive battery voltage down to 5V, which is the standard USB port power rail voltage. Since cellphones can draw up to 1A when charging from...
  11. KrisBlueNZ

    NiMh batteries problem

    I've heard of bogus rechargeable D cells that were made by putting an AA cell inside a D-sized case. Perhaps that's why they're so light.
  12. KrisBlueNZ

    power on 2 leds (red or green) on toggle switch (2 positions: on and off)

    Good answer GreenGiant!
  13. KrisBlueNZ

    Question about power delivery through standard 12v port

    Start by looking at the diagrams at https://en.wikipedia.org/wiki/Coaxial_power_connector. Many equipment-side sockets for this type of connector has three connections: one for the inner contact, one for the outer contact, and one for a "normally closed contact", which makes contact with the...
  14. KrisBlueNZ

    A few questions about transistor

    I assume you're talking about the "OK" diagram, with R3 present. This diagram shows typical operating voltages for a common emitter amplifier. You say that when a transistor is biased, its collector-emitter resistance should be minimum. That's only true when the transistor is saturated. In this...
  15. KrisBlueNZ

    Using Arduino to read bipolar signal (from plants)

    Regarding my previous suggestion. Changing the gain is not that difficult. It could be useful to be able to increase the differential amplifier's gain. Just change R1 and R2 (in my schematic). Their values must be the same. A double-pole slide or rotary switch could be used here. As long as the...
  16. KrisBlueNZ

    Using Arduino to read bipolar signal (from plants)

    This is what I suggest. I've tested it with various combinations of input voltages and it works as I expected. The output is biased at half the reference voltage and the differential gain is 1. I can't see any reason to adjust the differential gain in this application. Right. I have no...
  17. KrisBlueNZ

    Hitachi tv convergence issues

    Oops... looks like it's time to eat my words. Munch crunch... tasty... munch munch
  18. KrisBlueNZ

    How can I control a DC 12V motor

    D'oh! I didn't notice that your PIC is only running at 3.6V. With only 3.6V gate-to-source bias voltage, the data sheet does not specify a current rating or an ON-resistance figure. There's a typical graph that indicates that the MOSFET can still supply up to about 15A to the pump, but that's...
  19. KrisBlueNZ

    Help with power supply for pinball machine

    When you connect light bulbs in series, voltages add together and the current is the same for all. When you connect liight bulbs in parallel, currents add together and the voltage is the same for all. If your bulbs are already connected in parallel, you need to supply 6.3V to the bulbs, and...
  20. KrisBlueNZ

    Cold war electronics project....

    I'd like to see a readable version of that schematic...
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