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  1. KrisBlueNZ

    Time Delay Relay for caralarm-->gpstracker

    What are the electrical characteristics of the signal that you're sending from the alarm to the tracker? You say it sends a "pulse" but we need to know the electrical characteristics. Can you give the model numbers of the alarm and the tracker? Can you link to detailed information on them?
  2. KrisBlueNZ

    turn off circuit at low voltage

    Yes that's what he meant. Harald's circuit uses the series transistor as an emitter follower. To properly saturate the transistor, the base needs to be brought around 0.7V more positive than the emitter; since the collector-emitter voltage will be around 0.2V in saturation, this means that...
  3. KrisBlueNZ

    DC Jack spark

    It's normal. Most likely the customer just didn't notice it before. It's common for people to notice things after a repair that they didn't notice before. When you buy something new, and it works, you don't look closely, but when it has been faulty (before AND after it has been repaired)...
  4. KrisBlueNZ

    Photointerrupter latching encoder?

    Are you sure this specification makes sense? As your disc rotates, you would get "positive" and "negative" pulses alternating, won't you? In that case, every positive pulse will be followed by a negative pulse, and vice versa, won't it? I'm not really sure what you're looking for. I just want...
  5. KrisBlueNZ

    LED bulb dimmer

    Hi and welcome to the Electronics Point forums :-) There are various ways to do what you want. First, if you're controlling the digital potentiometer from a microcontroller, PWM generation can be done in firmware. Many microcontrollers include PWM generators on-board; for those that don't...
  6. KrisBlueNZ

    Alarm reset timer

    OK. I've updated the schematic to include some more information, and some component value changes that I hope will improve its handling of mains voltage spikes. Here's a list of components on Digikey. I'm not sure where you are. If you're not in America, you may find Digikey's shipping...
  7. KrisBlueNZ

    Changing the speed of a walkman motor with motion

    I don't understand why you want a power supply for the Walkman. The circuit I drew up provides the power to the Walkman. You don't need a separate power supply. If you want to power a Walkman without my circuit, you just need a 3V DC adapter. I'm not sure how much current a Walkman draws, but I...
  8. KrisBlueNZ

    Alarm reset timer

    Without a lot more information on the PIR circuit, I can't suggest a reliable hack. Here is a circuit that will close a relay after about 20 seconds. This circuit is powered directly from the mains, and should all be considered LIVE. It must be enclosed and insulated so that no part of the...
  9. KrisBlueNZ

    Pulsated LD

    Ah, I thought the CMOS versions would be better. Yes, the thresholds are 1/3 VCC and 2/3 VCC, which are symmetrical around 1/2 VCC.
  10. KrisBlueNZ

    Pulsated LD

    Sorry for not explaining myself Chris. I assumed you hadn't looked closely at the circuit and thought it was the usual arrangement using pin 7. The pin 2 and pin 6 threshold voltages are symmetrical around 1/2 VCC and pin 3 swings (nominally - ideally) between VCC and GND, so the duty cycle is...
  11. KrisBlueNZ

    Pulsated LD

    I think Chris would probably have guessed that you found it online. I think he was asking which site you got it from. BTW, the duty cycle of the first circuit IS roughly 50%.
  12. KrisBlueNZ

    Alarm reset timer

    Ah yes, good thinking. Power the delayed relay unconditionally, and connect its contact in series with the contact from the PIR.
  13. KrisBlueNZ

    Alarm reset timer

    Sorry for the slow response. I've been wondering how to respond. The circuit and the PCB seem to be very well designed. The LM324 is a very common IC, as you've probably discovered. The relay is driven directly from one of its outputs, on pin 14. The main supply rail is +24V (the relay has...
  14. KrisBlueNZ

    What value of resistors do I need and a sanity check

    I'm sorry, I don't want to try to advise any further on this subject. I want nothing to do with people who are using home-made circuits to pass current through live people.
  15. KrisBlueNZ

    Changing the speed of a walkman motor with motion

    I've made a correction to the design in my previous post. Two trimpots are really needed to fully control the circuit's response to illumination. I've added VR2, and changed Q1 from a BC557C to an MPSA64 or BC516. (Digikey don't stock the MPSA64 any longer.) VR2 (1M trimpot)...
  16. KrisBlueNZ

    Changing the speed of a walkman motor with motion

    The 423 and the 443 use fundamentally different motors and can't be controlled in the same way, so for simplicity, I think it would be easiest to have two of the same type of Walkman. As long as this isn't a problem from an aesthetic point of view. The 423 can be controlled by varying the...
  17. KrisBlueNZ

    Help with hooking up open collector outputs

    You're welcome. Nice work!
  18. KrisBlueNZ

    NPN circuit not behaving...

    But you said earlier: (Highlighting mine.) 39 mV is pretty low - low enough to be considered "low" by every discrete semiconductor and IC that I've ever heard of. And it's a lot lower than the minimum low threshold of the CE pin on that IC. So you haven't explained what the problem was.
  19. KrisBlueNZ

    Changing the speed of a walkman motor with motion

    OK. You can get more control over how the light affects the motor speed on the 443 model if you remove the speed control trimpot and replace it with a circuit containing the LDR, one or more resistors, and possibly other components as well. The 423 model is not so easy to modify. Can you use...
  20. KrisBlueNZ

    Alarm reset timer

    That's good, thanks. I need to know the markings on the IC on the underside at the left, marked U1. If there's some kind of goop covering it, try cleaning it with a cotton swab dipped into detergent diluted in hot water. You may need a magnifying glass and/or a very strong light to see it. If...
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