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  1. KrisBlueNZ

    Using $1 stereo amp in mono mode

    Hi there and welcome to Electronics Point :-) That board uses a PAM8403 stereo BTL output IC. You can't connect the two outputs of that amplifier together. You would have to use only one channel, and mix the left and right audio signals (from the wires from the headphone plug) into a single...
  2. KrisBlueNZ

    How can µF-range capacitors reduce AC voltage?

    I can't view your Google Docs page - I don't have permission.
  3. KrisBlueNZ

    Normal open door buzzer

    Hi Marc and welcome to Electronics Point :-) First, you need a way to detect when the door is opened. The usual way is with a little microswitch in the hinge area or elsewhere on the door itself. Many of the switches on this page will be suitable...
  4. KrisBlueNZ

    Random LED Colour Changer

    Depends on the circumstances I suppose. Yes, I would have thought so too. That circuit is pretty simple; a change to the odds would require more ICs. Could be done with a minor change. Surely this is more than just a rumour? It seems obvious that they would do that, even if (for reasons of...
  5. KrisBlueNZ

    Help with RS485

    Hi again and sorry for the delay getting back to this thread! I've reviewed the thread and I don't see how full duplex would help. All it means is that you could transmit data in both directions at the same time. Since you would probably use a poll and response protocol anyway, the only...
  6. KrisBlueNZ

    Constant signal triggering a pulse

    Then you just need a single edge-triggered monostable. You can use that circuit; just delete C1, R1 and the associated 10k resistor and link U1 pin 5 to the positive rail. You may prefer to buy a pulse relay that generates a pulse of defined duration when power is applied to it.
  7. KrisBlueNZ

    Random LED Colour Changer

    OK, here's my suggestion. It uses two ICs from the CMOS CD4000 series: one CD4093B quad NAND gate with Schmitt trigger inputs, which is shown as four D-shaped elements on the diagram, and one CD4013B dual D flip-flop. The circuit can be powered from 9~12V DC from a battery (its current...
  8. KrisBlueNZ

    Scoreboard project

    No problem. Just connect the relay contacts of the remote to the places where the pushbutton would have been.
  9. KrisBlueNZ

    Random LED Colour Changer

    It depends on what you mean by random. In this type of case, it's probably enough to have an oscillator running constantly, kind of like a coin that is always flipping, and when the button is pressed, the state at that time is captured and used to control the indication. If the oscillator is...
  10. KrisBlueNZ

    countdown timer

    You need to use the preset inputs. That's what they're there for. Set them for 30 and put an RC circuit on the preset enable input (pin 1) to preset the counters at power-up or on reset.
  11. KrisBlueNZ

    Scoreboard project

    Here's my recommended design. Right-click it and choose Save Image As then view it at 1:1 zoom in an image viewer. It requires a power source of 15V DC that's able to supply at least 2A. It uses twelve ICs - six CMOS 4000 series devices, five ULN2003 driver ICs and a 78L09 regulator IC...
  12. KrisBlueNZ

    Light following robot

    Sounds like there's not enough light falling on the LDRs. With the trimpots set for maximum resistance and light directed at the LDRs, the motors should definitely turn OFF; if not, your wiring is wrong. Once you've got that part working, you may find you need to increase the light falling on...
  13. KrisBlueNZ

    How can µF-range capacitors reduce AC voltage?

    LEDs do have some internal incremental resistance so the capacitor will have some effect. I ran a simulation to find out, but I had to change "CX" to about 0.47 µF (not "472", i.e. 4.7 nF, as shown in the original schematic, which I assume is a typo) to get significant LED current. LTSpice...
  14. KrisBlueNZ

    Transistor as a switch

    You might be able to use just two BC547 transistors, or a single Darlington transistor such as an MPSA14 which includes two transistors inside it. I decided on three transistors because I like to "play it safe" but I didn't go through the full calculations for a standard Darlington. You may find...
  15. KrisBlueNZ

    Transistor as a switch

    Yes. A small BJT (transistor) starts to conduct when VBE is around 0.6V and conducts more strongly as VBE is increased to 0.7V and 0.8V. You should have been taught this. Here is a graph showing how VBE relates to IC for a BC547B connected as shown in the schematic. BTW, I created this graph...
  16. KrisBlueNZ

    Stage Line 500W amp repair project

    Sorry Pete. I haven't been supporting you as I should have been. ----- First some notes on using your multimeter. I should have explained this earlier, and I think you've figured it out already, but it doesn't hurt to be clear. Always have the probes in the COM socket (black probe) and VΩmA...
  17. KrisBlueNZ

    Constant signal triggering a pulse

    Hi there and welcome to Electronics Point :) So you want a circuit that will generate a pulse when an input signal changes from OFF to ON, and another pulse when it changes from ON to OFF? This can be done with two monostables, one rising-edge-triggered and one falling-edge-triggered. Here's...
  18. KrisBlueNZ

    How can µF-range capacitors reduce AC voltage?

    The presence or absence of the 100 µF smoothing capacitor doesn't change the fact that the circuit is not safe, as I described in post #2. Edit: Using a 400V capacitor will stop it from exploding if the LEDs get disconnected, but if they get reconnected (for example if there's a dry joint or...
  19. KrisBlueNZ

    Making two if Statements work at the same time

    Merlin3189, I see what you're saying, but look at his original code, and especially, the indentation. And read his problem description carefully. The problem is that the second if() statement is only executed if the first if() evaluates to false, and the reason is just that he's missed a closing...
  20. KrisBlueNZ

    Help with fan controller using LM35

    You have to decide whether you want to switch the fan ON and OFF depending on whether the temperature is above or below a certain threshold, or whether you want to vary its speed according to the temperature. In other words, you need to draw a graph with temperature on the horizontal axis, and...
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