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  1. KrisBlueNZ

    PCF8575- the chip died

    Yes, as Harald says, please show us the schematic of your circuit. A photo of the construction could help as well. Also please describe the external I/O devices you are connecting to it.
  2. KrisBlueNZ

    Simultaneous events

    Any small microcontroller can do this, but you should investigate ones that have USB interfaces built-in. Some of the larger PICs have this, I think, and some of the larger AVRs. You can scan multiple buttons in a grid using multiplexing, to reduce the amount of I/O needed. You need to use...
  3. KrisBlueNZ

    Designing a Time Delayed Relay

    OK, I've gone for a circuit that's permanently powered from 110VAC, doesn't use a transformer (uses a "capacitor fed" power supply), and gets its timing from the mains. It uses two ICs, but it's pretty accurate and doesn't need any adjustment. I hope you don't think it's too complicated to...
  4. KrisBlueNZ

    Hi, pretty basic question about a simple CMOS TTL circuit

    That schematic won't work. I think you have the two diodes drawn backwards. I agree with what kpatz said in post #15. The SolSIG signal, that feeds through the resistor to the anode side of the LED, must come from a signal that is only +12V while the hazard flashers are turned ON. At all other...
  5. KrisBlueNZ

    help in speed changing

    You use PWM to control the average voltage to the motor. Wider pulse width = higher average voltage = motor turns faster.
  6. KrisBlueNZ

    telephone circuits

    I don't have much faith in that design. Let us know how it goes :-)
  7. KrisBlueNZ

    Which voltage transformer for a laser printer

    It's POSSIBLE. As I said in the other thread, don't get your hopes up. But it's worth a look.
  8. KrisBlueNZ

    telephone circuits

    It sounds like you have it well in hand. One thing I can suggest is that POTS lines and phones use only two wires and pass audio in both directions. The carbon microphone and the earpiece are connected in series at each end; the two ends are connected in series, and DC (48V) with a series...
  9. KrisBlueNZ

    Digital clock - light variant

    Hello and welcome to Electronics Point :-) Can you post the schematic that you tried, and the range of output voltages you were getting from it?
  10. KrisBlueNZ

    Need help with remote firework detonator

    I tend to agree with Bob. Walkie talkies are designed to allow kids to have fun, not to be a secure form of communication. And it's not just other walkie talkies that could trigger your igniter. You could probably improve reliability by sending a specific signal, e.g. a tone at high amplitude...
  11. KrisBlueNZ

    Avoiding collisions in RF setups.

    Yes, random intervals are a good idea. Alternatively you could calculate the retry interval based on the sensor's address, since (presumably) each one has a different address or identifier.
  12. KrisBlueNZ

    relay to power a 12v bilge pump

    OK, that's a pretty small current requirement. The two items you linked to are both overkill - they can supply several amps, and they are switching regulators, which are designed for high efficiency. The first one specifies an input voltage range of 11-28V so it has a dropout voltage of 2V. If...
  13. KrisBlueNZ

    help in speed changing

    Yes: PWM. http://www.google.com/search?q=how+does+pulse+width+modulation+PWM+work
  14. KrisBlueNZ

    Stereo amplifier volume fades over time

    I would definitely throw the old one out. You will never get it very flat, unless you have some kind of industrial press! Good point. If it's attracted by a magnet, and it's a dull grey colour and somewhat soft (easily gouged with pliers to a small depth), it's probably mild steel, I think.
  15. KrisBlueNZ

    Designing a Time Delayed Relay

    Thanks :-) Yes you're right, an RC circuit will not be very accurate. Capacitors that can produce delays around 30 seconds are generally aluminium electrolytic types, which have an accuracy of ±20% (unless you special-order them from the manufacturer in big quantities), and that's only the...
  16. KrisBlueNZ

    telephone circuits

    Do you want to use telephone handsets? Or a loudspeaker that you talk into while pushing a button? Or do you want to use two standard wired or cordless telephones? What power sources are available at each end? How many wires do you want to use between the two ends?
  17. KrisBlueNZ

    Which voltage transformer for a laser printer

    That looks like quite a nice laser printer. It draws quite a lot of power. You would need a step-down transformer rated for at least 1 kVA, to be safe, I think. We had a similar thread here recently: https://www.electronicspoint.com/threads/voltage-converter-120v-to-220v.268341/ I suggested...
  18. KrisBlueNZ

    Stereo amplifier volume fades over time

    Yes I see what you mean. The one on the right is pretty mangled, and that would be a likely reason for the problem. That bit of metal seems to be a spacing shim that conducts heat from the IC to the main heatsink. It looks like it's made from mild steel, I think. It needs to be very flat on...
  19. KrisBlueNZ

    Designing a Time Delayed Relay

  20. KrisBlueNZ

    Designing a Time Delayed Relay

    I don't know what a NOTO relay is, but yes, an electromechanical relay will switch your inductive load. The contacts should have a "snubber" circuit across them to protect them from arcing when they switch OFF. I'll cover that in a later post. Yes, commercial time delay relay units can be...
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