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  1. KrisBlueNZ

    Microcontroller controlled by pushbutton for LED flashlight

    Yes, roughly, over the working range (0~5A in your case).
  2. KrisBlueNZ

    Help: how to wire a potentiometer ?

    Hi Chris and welcome to Electronics Point :) That's a fair question. Potentiometers and preset potentiometers (trimpots) have a resistive track with two end terminals, and a wiper that moves along the track. This is clear from the trimpot in the right of your photo, where the wiper corresponds...
  3. KrisBlueNZ

    Wireless doorbell melody change

    Hi Alex and welcome to Electronics Point :-) I guess U3 is the 555? No, a 555 does not produce a melody, it's a simple timer IC. The melody generator could be U1 on the underside (I can't see the markings on it) but is more likely to be on the daughter board labelled U2. The six-element DIP...
  4. KrisBlueNZ

    countdown timer

    OK, here's my redesign. A lot of it is the same but I've changed how the preset and clear inputs of the 4510s are driven. IC6, the 4081 (or is it IC7, the 74LS08?) is no longer needed, and I've added a 4013 dual D flip-flop. I'll only describe the changes here. On power-up, CR and RR produce...
  5. KrisBlueNZ

    Swamped Amplifier Design

    OK. So at the moment, VB is around 0V because the input is DC-coupled, so VE is about -0.7V, and VOUT(p-p) is limited to around 10V, because the transistor can only pull its collector down to slightly above VE. If you want to make better use of the 20V available, you will have to change the...
  6. KrisBlueNZ

    Swamped Amplifier Design

    Hi Samson and welcome to Electronics Point :-) In your diagram, VCC is marked "0V". That should be +10V, right? Also, is VEE -10V? And the junction of RE1 and RE2 is also labelled "0V". That can't be right; it must be around -0.7V. Is your circuit supposed to have a DC coupled input? If so...
  7. KrisBlueNZ

    Constant current Source clarification

    I don't know offhand. Are you asking me to look at the data sheets for you? I explained the reason for the problem and showed you which graph to look for on the data sheet. You're a grown-up now, you need to be able to do these things for yourself! BTW another option that I mentioned in post...
  8. KrisBlueNZ

    Microcontroller controlled by pushbutton for LED flashlight

    Yes that may be OK. 17 mΩ at 5A will dissipate 425 mW. That seems pretty high for such a small package without an intimate bond to the PCB. Have a look at these documents: www.analog.com/static/imported-files/tutorials/MT-093.pdf ww1.microchip.com/downloads/en/AppNotes/00792a.pdf...
  9. KrisBlueNZ

    Microcontroller controlled by pushbutton for LED flashlight

    Right. The PIC10F200 is the same size and a bit cheaper, and is also up to the task. ATtiny4: http://www.digikey.com/product-detail/en/ATTINY4-TSHR/ATTINY4-TSHRCT-ND/2477315 USD 0.69@100x PIC10F200: http://www.digikey.com/product-detail/en/PIC10F200T-E/OT/PIC10F200T-E/OTCT-ND/2178264 USD...
  10. KrisBlueNZ

    Constant current Source clarification

    Have a look at this graph from the data sheet. This graph tells you how much voltage you need between the gate and source of the output MOSFET (the -VGS value) to make it conduct properly. At VCC=5V and with 2.5V across the source-to-VCC resistor (R1), even with the op-amp output all the...
  11. KrisBlueNZ

    Microcontroller controlled by pushbutton for LED flashlight

    Yes, you're on the right track. I would use a small micro such as an ATtiny or a PIC10F200 for an application like this. You could do it with discrete logic but it would be physically quite a lot bigger once you include latch/unlatch and debouncing. Why do you need two MOSFETs? Does the output...
  12. KrisBlueNZ

    IRF640 vs IRF640N

    I've asked Steve for his advice.
  13. KrisBlueNZ

    Stage Line 500W amp repair project

    Good. So you can remove the bridge across Q2 (from post #138). Then when you've removed all the brown goop, we can get back to checking the output stage!
  14. KrisBlueNZ

    countdown timer

    Yes, you're right. So can you confirm that the behaviour you want is: On power-up the count indicates 30 but does not count down When the button is pressed, the countdown starts When the count reaches 00, it stops That's not an easy change; it will probably require another IC. I will draw up...
  15. KrisBlueNZ

    Stage Line 500W amp repair project

    Sure, put Q46 back into circuit.
  16. KrisBlueNZ

    IRF640 vs IRF640N

    Yes, I think you're probably right. You missed an N suffix somewhere in that sentence. I don't know enough about MOSFETs to say what the difference might mean. It might just be a difference in convention between manufacturers. Are those data sheets with the different diode symbol from the same...
  17. KrisBlueNZ

    Stage Line 500W amp repair project

    Yes, definitely. I know it's used for rigidity but I doubt that it's hot melt glue as such. I've seen that stuff cause problems before when it gets old. It can corrode wires. That 27 kΩ resistor is not in an unusual circuit position. The reasons why it might have failed are (a) random failure...
  18. KrisBlueNZ

    Stage Line 500W amp repair project

    LOL! The colour codes on those resistors say 6.8 kΩ. Did Maplin sell you those when you asked for 27 kΩ resistors? They must have got moved into the wrong bin. And I guess the staff don't know what the little coloured stripes mean - perhaps they think they're for decoration, like on beads on a...
  19. KrisBlueNZ

    Tips for learning recursion?

    I agree that the decision to use recursion should not be taken lightly. Code needs to make sure the termination condition will be reached within a reasonable number of recursions and the implications for the stack need to be clearly understood. I think it's a matter of risk and severity of...
  20. KrisBlueNZ

    Tips for learning recursion?

    Hi Don. It uses a word list file, which I created from various online sources whose locations I did not keep track of! It includes lots of "words" that aren't words (initialisms, etc) because I wanted to maximise the number of matches and filter them manually. It's about 1.2 MB and ZIPs down to...
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