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  1. KrisBlueNZ

    How to remove Araldite?

    Sorry if this seems obvious, but have you contacted the manufacturer of the "Araldite" product you are using and asked them if they know of any way to dissolve it?
  2. KrisBlueNZ

    Need help with Arduino Atmel project

    Yes, you will need to use an ADC. An ADC measures the voltage on its input, and convert it to a number that represents the position of that voltage on a scale between the negative and positive reference voltages that are fed into the ADC. Usually the negative reference is the 0V (ground) rail of...
  3. KrisBlueNZ

    Audio interface to microcontroller?

    You had the right idea initially. Use a series capacitor from the input jack to the ADC, and a resistor from the ADC input to a 2.5V reference voltage to centre the ADC input at half scale. For the output, all you need is a series capacitor between the DAC output and the jack connector. You can...
  4. KrisBlueNZ

    AC Solenoid valve driver circuit

    There are many ways to control an AC-powered solenoid. The simplest is a relay, which is an electrically controlled switch. You can get these in a range of types, with coil (control side) voltages of 3.3VDC, 5VDC and higher. Even a fairly small relay can switch 24VAC at 90 mA. That is no...
  5. KrisBlueNZ

    Transistor Gain

    If you want any really useful answers, you need to explain a lot more about what you're doing. Can you post a schematic? Can you tell us why you need to know the number? Do you have a particular transistor in mind? Are you designing a circuit to work to a particular specification? We're playing...
  6. KrisBlueNZ

    About LED Sign Board

    Have a good look at this explanation: https://www.electronicspoint.com/got-question-driving-leds-another-work-progress-t228474.html That tells you about LEDs and how to drive them. I assume you want to make an animated, multi-colour sign board. This requires multiple LED drivers, like a...
  7. KrisBlueNZ

    Help with time delay relay circuit

    Right... There are lots of spray-on and brush-on coatings available. Mouser have a range of them - look in the "Tools and Supplies -> Chemicals" category and choose "Coating products" and "Sealants". The coating will seal everything completely, so you'll need to choose your trimpot setting...
  8. KrisBlueNZ

    Help with time delay relay circuit

    "100R" = 100 ohms.
  9. KrisBlueNZ

    Can I just simply replace inductor with a choke?

    If he's so concerned about reliability, a mains-powered SMPS is a bit of a liability. They do tend to go pop in response to voltage surges. Of course if he's aiming for high efficiency, it's the obvious answer, so there's a conflict there. Perhaps there are mains-powered switching supplies that...
  10. KrisBlueNZ

    Help with time delay relay circuit

    OK, it's up to you how you do it. The drive from Q4 is no more than 500 mA, and I assumed it would be driving a relay coil that draws 160 mA as you said earlier. The drive is normally not present, and becomes active when it's time to kill the engine. So I guess you would use the normally closed...
  11. KrisBlueNZ

    Help with time delay relay circuit

    From what Andy said, I think it has separate coils, and the hold coil is the one that draws nearly 9A. I assume the energise coil is operated by a separate pushbutton. It's not part of this circuit. Andy, can you clarify this? Yes, I thought that would be a GOOD thing... People are more likely...
  12. KrisBlueNZ

    Can I just simply replace inductor with a choke?

    Thanks for that. That gives us some idea what you're talking about. Yes, electrolytics do eventually dry out and fail, but in a design like this it's going to be difficult to avoid them. When you're working with mains frequency, you need to "fill in the gaps" in the waveform somehow (assuming...
  13. KrisBlueNZ

    Can I just simply replace inductor with a choke?

    A load current of 0.5A from a 15VAC mains transformer is not much. If you need a clean supply rail, have you considered using a regulator to remove the ripple? You really are wasting our time by feeding little bits of information one at a time. Please post a schematic that shows everything you...
  14. KrisBlueNZ

    Can I just simply replace inductor with a choke?

    Current is measured THROUGH a component, not ACROSS it. Also, if you pass 0.5A through a 100 ohm resistor, it will dissipate 25 watts, not 50 watts. No one is suggesting that you use a 100 ohm resistor. I would use a few ohms, if your application is anything like what I imagine it is. I think...
  15. KrisBlueNZ

    Active low or active high signalling?

    I suspect he doesn't have the option of using a twisted pair. I guess the signal will have to go through a wiring harness and that may have been defined already.
  16. KrisBlueNZ

    Help with time delay relay circuit

    OK, here's an updated schematic. This design uses two transistors instead of the 555 and it doesn't need as much protection against spikes on the supply rail. I've added the second float switch and the indicator LED, and a piezoelectric beeper that will sound while the bottom float is low and...
  17. KrisBlueNZ

    Valve (tube) amplifier schematic help

    Yes, the voltage gain of the stage depends on the transconductance and the anode load resistor. The transconductance determines how the anode CURRENT varies in response to the grid voltage, and the anode resistor converts that varying current into a varying VOLTAGE. The voltage gain is equal to...
  18. KrisBlueNZ

    Valve (tube) amplifier schematic help

    Yes, that's a fair way of looking at it. The input signal just controls the active element; all of the energy in the output signal comes from the power supply. A common cathode Class A amplifier can't be more than 50% efficient, but as a small-signal voltage amplifier, it isn't designed for...
  19. KrisBlueNZ

    Valve (tube) amplifier schematic help

    Thanks :-) And thanks Chris. I think you've got it pretty well. I have a few corrections to your terminology. Yes, "coupled" to the grid, normally through a coupling capacitor, which couples the AC signal while leaving the DC bias unaffected. "Bias" refers to the static conditions (voltages)...
  20. KrisBlueNZ

    Help with time delay relay circuit

    OK thanks for the description. I'm no tractor expert, but that looks pretty tidy :-) I have a few more questions. Are the float switches fully isolated from each other and from everything else on the tractor? So you just have two 2-core wires, one from each float? The fuel shutdown holding...
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