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  1. KrisBlueNZ

    Lab supply

    Try shorting pin 8 to ground. If that allows it to turn ON, find out why pin 8 is being pulled up when the circuit tries to start up. The TL431 should be pulling it low when the switched supply rail goes higher than the low voltage cutoff.
  2. KrisBlueNZ

    Lab supply

    Hi Greg, Let me get this straight. Correct me if I'm wrong. The first half of the 4013 (top, in the diagram) generates a positive pulse on its Q output each time the pushbutton is pressed. This pulse is supposed to turn the circuit ON if it's OFF, and OFF if it's ON. The second half of the...
  3. KrisBlueNZ

    ds1307 with atmega32 in assembly

    Hello and welcome to Electronics Point. I can't help with your program because I'm not familiar with the ATmega32's I2C peripheral, but I did notice something you should fix. In the DS1307 data sheet, page 7, the description of Vbat pin says "If a backup supply is not required, Vbat must be...
  4. KrisBlueNZ

    simple usart problem

    Your interrupt handler has to clear the RCIF flag. If you don't do that, as soon as you return from your interrupt handler, the interrupt will trigger again. You should not be calling lcd_putch() from inside your interrupt handler. You should use a global array with global offsets or pointers...
  5. KrisBlueNZ

    Powering a flyback transformer

    You won't get much voltage out of it. The way flyback transformers are driven is: A component (transistor or MOSFET, usually) completes a circuit and allows current to flow from a DC supply into the primary winding. The current, and the magnetic field in the core, builds up according to the...
  6. KrisBlueNZ

    Irrigation controller repair

    Fair enough. Disappointing, but... you win some, you lose some, I guess :-)
  7. KrisBlueNZ

    Irrigation controller repair

    Hmm. I don't think it's gonna happen. There's nothing visibly damaged, and no components that are easy to test or likely to tell us anything, apart from the PTC fuse which you've already checked. If you bought a multimeter, you could check the supply voltages on the microcontroller, the output...
  8. KrisBlueNZ

    New Here---Novice

    Hi Orlando, and welcome to Electronics Point :-) With an unfamiliar unit like this, I would start with the multi-pin components. Your first photo shows a 16-pin SOIC (small outline IC) on the track side, and the second photo shows a 24-pin DIP (dual in-line package) on the other side. There are...
  9. KrisBlueNZ

    Irrigation controller repair

    Ah well, it was just an idea. Could you upload some closeups of the front side of the board so that the IC part numbers are readable...
  10. KrisBlueNZ

    Irrigation controller repair

    As you say, it all looks fine. Here's one suggestion though. In the bottom right corner, the red component above the right hand end of the fuse is a "PTC fuse". Power up the unit with the front cover off, wait for it to power itself off, and see whether that component is hot or not. If it's hot...
  11. KrisBlueNZ

    Help me understand my scope trace result on a IR photocoupler.

    Are you sure? Does the photointerrupter have any markings on it? If so, Google them and see if you can find a data sheet. That will tell you what the wires are for. Right. Four-terminal photointerrupters have open collector outputs - they're just like a four-terminal optocoupler but with a gap...
  12. KrisBlueNZ

    Irrigation controller repair

    Hello Harry and welcome to Electronics Point :-) I found Holman Industries' web site at http://www.holmanindustries.com.au but there's no mention of an 8400 model. I guess it's obsolete now. My first thought is that it thinks there is a problem and is shutting down as a safety precaution. Read...
  13. KrisBlueNZ

    Help with simple relay circuit

    That's a neat little circuit Harald. It will always power up in a defined state.
  14. KrisBlueNZ

    Help with simple relay circuit

    I think the word "toggle" may be causing confusion. A "toggle" switch has a long shaft that you use to flip it between two or more positions. In the sense I used it in post #8, "toggle" means to alternate between two states. So you push the button and the circuit flips to state 1, push the...
  15. KrisBlueNZ

    Why Circuit not outputting max voltage?

    Steve, you're on a roll! That's the third excellent and helpful post I've seen from you in the past few days :-)
  16. KrisBlueNZ

    audio transformer

    Yeah that brings back memories! If it's the one I'm thinking of, it was a Hartley oscillator. The centre tap connected to the supply rail (negative, if you're using a 2SB56, which is - was - a germanium PNP). The collector connected to one end of the primary, and the base was driven from the...
  17. KrisBlueNZ

    Electronic Engineer

    Or freelancer.com
  18. KrisBlueNZ

    Help with simple relay circuit

    If you want a circuit that toggles between two states when you push a button, have a look at https://www.electronicspoint.com/need-help-needed-circuit-t254020.html#post1508062 It uses a latching relay. It will power up in whatever state it was in before it was powered down, which doesn't fit...
  19. KrisBlueNZ

    Scoreboard Project

    gorgon, it looks like we're going ahead with seven 20-pin PICs in narrow DIP packages. EPROMs would have worked, but fourteen 24-pin or 28-pin wide DIPs would be much larger, and anyway, Dave is keen to get involved with microcontrollers. Thanks for your offer though.
  20. KrisBlueNZ

    Car audio problems: MP3 player into CD changer socket

    I don't know why it stops working after a few trips. I need to find out more about how everything fits together. So the MP3 player connects to just the "B" connector, right? Can you take a photo of the back of the plug that shows which pins are used, and what each one connects to? Can you...
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