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  1. KrisBlueNZ

    Potmeter help

    Do you mean "potentiometer"? Does your potentiometer have 11.1V on one end, and 0V on the other end? Is that what you're trying to say? It needs to be connected between some voltage and 0V, and its 0V connection needs to connect to the micro's 0V rail. Then you use a voltage divider to reduce...
  2. KrisBlueNZ

    Guitar Amp Modification

    So this "tuner" thing isn't a tuner, it just needs to detect which note is being played and light the appropriate LED? There are twelve semitones (aka "half-steps") in an octave, so I assume you'll want twelve LEDs, is that right? Or do you want a separate set of twelve LEDs for each octave? If...
  3. KrisBlueNZ

    diy logic probe

    Hmm... I seem to recall a thread on this subject last year. It was started by... a user called... foTONICS! Thread: https://www.electronicspoint.com/logic-probe-t248819.html Post with my suggested diagram: https://www.electronicspoint.com/logic-probe-t248819.html#post1471120 The design I...
  4. KrisBlueNZ

    Help with "Data switch"

    Asynchronous serial data uses a single signal for each data path. (RS-422 and other differential systems use two wires per signal, but there is still only one signal.) That signal is digital, i.e. it is always in one of two states. One state is defined as "idle" or "mark", and the signal stays...
  5. KrisBlueNZ

    Help with "Data switch"

    I don't understand what you're asking regarding skipping the circuit. You will need some kind of timing circuit, because the data line will be changing state as the data is transferred. When the data stops, the line will go idle, which for RS-232 is negative, although if the GPS receiver loses...
  6. KrisBlueNZ

    Help with "Data switch"

    Yes, that circuit should work. R2 isn't needed, and the transistor should be a BC557B or a 2N3906. (The BC157 suggested is an obsolete part.) You'll need to process the RS-232 signal. The idle state for RS-232 data is negative, so you need a circuit that detects when it goes positive (data...
  7. KrisBlueNZ

    Help with "Data switch"

    Well, if you're sure that the PC software will not mind having a new GPS suddenly appear, and you only care about complete loss of the data stream, you can do what galaxy suggested. A 555 in monostable mode, triggered from the data stream from the GPS to the PC, will keep the relay switched over...
  8. KrisBlueNZ

    help with circuit design

    Hi and welcome to the forums :-) Yes, you can do that. It's not difficult. You can use the ubiquitous NE555 (just called the "555") to control the relay(s). Does this reversing voltage need to be a "one-shot", i.e. a single sequence triggered by a pushbutton, or a continuously repeating...
  9. KrisBlueNZ

    Help with "Data switch"

    You can use a relay to switch the serial data signals between two different GPS receivers, but you've already identified a problem with your whole idea: how do you detect when one of them has failed? The only way to reliably do this is in software on the PC, which is able to analyse the...
  10. KrisBlueNZ

    Project design help

    That circuit should work fine. The connection between the two stages is the transistor, which acts as a buffer between the first oscillator and the second oscillator and modulates the frequency of the second oscillator through pin 5 of the second 555. You've already checked that your rising and...
  11. KrisBlueNZ

    Circuit help - Motor controller

    Google stepper motor tutorial. The first six hits, at least, look pretty good. Stepper motors are driven from DC which is switched by semiconductor devices, usually MOSFETs.
  12. KrisBlueNZ

    help with designing a circuit

    For the current source, at 15V supply, somewhere between 3A and 10A is the dividing line between "not too difficult" and "very big with significant obstacles". Of course, you first need a regulated DC power supply that can provide the current. A laptop power supply could be a good choice here...
  13. KrisBlueNZ

    help with designing a circuit

    I'm not sure what you're suggesting. You can (and should) have a smoothing capacitor across the 555 oscillator part of the circuit, to make sure it's not affected by power supply variations caused by the heavy charge current for the 1F capacitor (assuming the control circuitry is powered from...
  14. KrisBlueNZ

    LED timer

    I've got a schematic drawn up. I just need answers to those questions.
  15. KrisBlueNZ

    help with designing a circuit

    Right, an incandescent bulb is the opposite of what you want. The formula for charging a capacitor is: dV / dT = I / C so if I = 5A and C = 1F, the capacitor voltage will rise at a rate of five volts per second. So it would take three seconds to charge from 0V to 15V. I don't think it would...
  16. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Yes, you can go up to 2A. The limit is the power dissipation in the transistor. You mustn't exceed its rated dissipation, which is 60W. There is also a safe operating area limit, shown in the data sheet as a graph of collector voltage versus collector current. According to the SOAR graph in the...
  17. KrisBlueNZ

    help with designing a circuit

    That's all exactly right. You will want some way to limit the charging current flowing into the capacitor, especially if you plan to use a 1 farad capacitor. A discharged capacitor will try to draw an extremely high current (limited only by the resistance in the circuit, which includes the...
  18. KrisBlueNZ

    help with designing a circuit

    Yeah, I thought that too. "Clicky clicky noise, sounds cool!" For the first ten minutes or so. You'll need one DPDT (also called DPCO) relay for each capacitor. Here are some examples of DPDT relays. They all have 12V coils, but other coil voltages are available. 2A contact rating...
  19. KrisBlueNZ

    help with designing a circuit

    Ah, but you will be when you test it! You'll probably be alright with small relays, but those big ones... after ten or fifteen minutes... Arrrrggggggh!
  20. KrisBlueNZ

    help with designing a circuit

    Does the capacitor need to be completely disconnected from the drive circuit when the load is connected? Like in a switched capacitor power isolator? Or can one terminal of each capacitor stay connected to the ground rail of the driving circuit? If there's no need for full isolation, you can...
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