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  1. KrisBlueNZ

    lighting a 7 segment LED

    Emitter follower? To use a transistor to increase the output current capability of a microcontroller pin that is driving the segment pin(s) of one or more seven-segment LED displays: Base driven directly by I/O pin that controls the segment. Collector tied to VCC (for common cathode displays...
  2. KrisBlueNZ

    help in tracking system

    Good movie! I doubt you could use an old mobile phone as a GPRS modem. I think you will need to get a real GPRS data modem. There are many manufacturers. Google cellular modem or GPRS modem.
  3. KrisBlueNZ

    lighting a 7 segment LED

    Other possible reasons for the display being dim when more segments are lit are: 1. The microcontroller may not be able to supply the necessary current when several outputs are driving LEDs directly. In this case you can use emitter followers between the outputs and the segments. For common...
  4. KrisBlueNZ

    HP 1741A Oscilloscope

    Have you measured between transformer plug pins 14 and 15 with the plug removed from the board?
  5. KrisBlueNZ

    Rewiring 7-band EQ

    Good! Yes you should replace the cable. Connect the earth wire to the chassis using a screw through a hole into a nut, or a self-tapping screw if the chassis is strong, that is not used for any other purpose, with a solder tag for the wire and at least one lock-washer. The cable must enter...
  6. KrisBlueNZ

    HP 1741A Oscilloscope

    Are the references and part numbers readable on those schematics in any of the versions you have there? If so, could you post readable versions of both (A15 and A16) schematics please.
  7. KrisBlueNZ

    HP 1741A Oscilloscope

    Yes, that seems likely. If you can unplug the secondaries from the board they feed, you should see the voltage increase to normal. Post the LVPS schematic here if you like.
  8. KrisBlueNZ

    ATX Power Supply

    Huh, you're right. I assumed that automotive batteries would be the same voltage as sealed lead-acid (SLA) or valve-regulated lead-acid (VRLA) batteries, but they aren't.
  9. KrisBlueNZ

    HP 1741A Oscilloscope

    OK, here are a few things you can try. With the unit powered down: Disconnect the feed from the transformer (pin 7 I think) to the "HV MULT" unit (tripler) that feeds the final anode of the CRT. Triplers can be unreliable and a faulty one will stop the oscillator. Pull the PCB out and check...
  10. KrisBlueNZ

    7 Transistors Triangle Wave Generator (650Khz)

    Well, I've had a quick try to come up with a design that works better, with some success, but it's not much good at high frequencies. It's similar to design 3, with a 1 mA current sink that runs all the time and a 2 mA source that's gated. The capacitor is buffered by an emitter follower with a...
  11. KrisBlueNZ

    7 Transistors Triangle Wave Generator (650Khz)

    OK, that looks alright doesn't it. iimagine, when you prototyped your first circuit, what type of transistors did you use for the current mirrors? I don't expect that the distortion was caused by thermal mismatch; just curious. Also how did you construct the prototype? On breadboard? If so...
  12. KrisBlueNZ

    ATX Power Supply

    Well, butter my buns! That's not a bad instructable. He does say that he removed his fan altogether, which is not a good idea if you're going to be loading the power supply heavily, but apart from that it's OK. It will not be suitable for charging a sealed lead-acid battery though. As I said...
  13. KrisBlueNZ

    ATX Power Supply

    A crowbar is a circuit that shorts out an output of the power supply if a problem is detected. Usually this problem is over-voltage, and the crowbar is there to protect components downstream of the power supply from damage due to overvoltage if the regulation in the power supply fails. The name...
  14. KrisBlueNZ

    HP 1741A Oscilloscope

    OK, good. Now what's the current state of the unit? What are the symptoms exactly?
  15. KrisBlueNZ

    HP 1741A Oscilloscope

    Perhaps you should post that schematic! The one you posted in post #5, which I have been working from, doesn't seem to have a Q5.
  16. KrisBlueNZ

    HP 1741A Oscilloscope

    I don't know about the unit you have. I was saying that the circuit description does not seem to match the schematic. Not fully, anyway. I suppose that could be due to OCR errors but I'm not convinced. Can you check the references to Q4 and Q5 in the explanation are correctly OCRed, and see if...
  17. KrisBlueNZ

    ATX Power Supply

    If you answer my question I will do that, yes.
  18. KrisBlueNZ

    ATX Power Supply

    Oh dear. Can you post the link to the article on instructables.com please?
  19. KrisBlueNZ

    reverse engineering help

    Good! Thanks for the feedback.
  20. KrisBlueNZ

    broke my chair again

    Yeah, I used a gym ball for a while. It was quite comfortable. You have to be careful not to drop hot solder on it though! And keep the floor clear of component leads.
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