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  1. duke37

    Unstable latching circuit`

    The diode (rectifier) is not necessary. They are fitted to reduce the voltage when an active device is turned off. In the case of the SCR it will only turn off when the power supply is removed i.e. it cannot be turned off. A diode is a rectifier but 'diode' is often used for fast, small...
  2. duke37

    Car Parking Sensors Help Needed

    I had a talk with my neighbour who has an Audi. As an object is approached, the frequency of the beeps rises and eventually there is a constant tone. Also, the frequency of the note rises so that it would be difficult to make a narrow filter to select it. I have never played with audio...
  3. duke37

    Amplifier noise/heat up the wazoo (TDA2009)

    "I metered the outputs on the PCB, and both speaker outputs have DC across them, 5.3v on one, 5.2 on the other. What does that mean ?" What do you mean by speaker output? The amp output or the speaker input after the capacitor? The DC level of the amp output should be at about half the...
  4. duke37

    in need of some comparator help

    Welcome to the forum. You could look up the data for the LM3914 bargraph display driver. This has 10 comparators and you can connect to the appropriate outputs. It has a built in voltage reference.
  5. duke37

    Unstable latching circuit`

    A voltage regulator is nothing like a thyristor. I assume that what you have is a 12V regulator and will need over 14V in. You will not have this on a bike. Maplin sell a CP106D SCR (400V, 2A) UM74R. This should do to drive any relay coil that you have.
  6. duke37

    Unstable latching circuit`

    Some comments about your circuit. 1. The base of the BC547 should have a resistor to ground , say 10k, to ensure that it turns off. 2. R3 could be dropped to 10k. 3. The load of a resistor and led is not suitable since the led will not pass significant current until its turn on voltage is...
  7. duke37

    Unstable latching circuit`

    This is a common problem and is used with motor contactors. You do not need any transistors. Use a 12V relay which is switched in with your push button. Use a spare set of contacts to supply power to the relay when it is pulled in. The output will not come on until the button is pressed and...
  8. duke37

    Amplifier noise/heat up the wazoo (TDA2009)

    The circuits that I have seen have a 100nF capacitor across the power supply and also a big fat electrolytic. You do not have the electrolytic. The volume control normally has the wiper as the output. You have put yours in the other way round so that when the control is at minimum, there is a...
  9. duke37

    Amplifier noise/heat up the wazoo (TDA2009)

    You should look at the output of the amps for signs of instability. If the output capacitors are connected the wrong way round, they will short the amplifiers when the speakers are connected. Check for DC across the speakers. The volume controls are connected in an unconventional way. Is...
  10. duke37

    Amplifier noise/heat up the wazoo (TDA2009)

    The amps feed a Zobel network which will provide a heavy load on the amp at high frequencies. Does the amp get hot with no external load? You have to stabilise the amp (no white noise) with appropriate capacitors near the amp. If you have a scope, check for high frequency oscillation.
  11. duke37

    AC Relay/Contactor Powered by DC

    Contactors are slower than relays. They use a bar which is thumped up to a pair of contacts so when the contactor is opened, there are two contacts in series. There are guides to separate the arcs of the different phases. Have you considered a solid state relay?
  12. duke37

    Pc program calculates voltages,currents etc etc in a circuit

    There are many spice programs. I use 5spice and LTspice. The free version of 5spice is limited in size. Quite complicated circuits can be simulated in LTspice. LTspice seems to be the most popular on the forum. You should chose one and learn how to use it. I first used ECA, a commercial...
  13. duke37

    AC Relay/Contactor Powered by DC

    A DC relay run on AC will buzz a lot since the magnetic field reverses and passes through zero. An AC relay has a shaded pole. Part of the pole is surrounded with a copper ring. This produces a phase shift so that the total magnetic force never drops to zero. The ring carries current so...
  14. duke37

    Protecting Driver Transistor from Transformer/Coil Back EMF

    I don't have broadband, only slimband so it takes me ages to look up details of devices which you could doubtless provide with little difficulty. You have not said what the transistor is driving, I would expect a car ignition coil to generate more than 100V on the primary. A high voltage is...
  15. duke37

    DC Controlled AC Load

    The term isolation is used to describe the case where there is no connection between two parts of the system. A transformer can have isolation if the input and output windings are not connected together. A relay can have isolation as the coil pulls in the contacts with an insulating part...
  16. duke37

    Precise Half-wave rectifier problems

    Should one diode be connected the opposite way?
  17. duke37

    DC Controlled AC Load

    I would think that the diagram as shown by Dave would work, It is used to measure AC current with a DC meter and some TVs used this circuit with two of the diodes replaced with thyristors to control the voltage but here he load was after the rectifier. The output can not be connected to a...
  18. duke37

    Can it be done?

    It is not a good idea to use a dimmer to drive a transformer because there could be assymmetry between positive and negative parts of the waveform. This could lead to saturation of the core and large currents flowing. You can do this if you put a resistance in series such as a light bulb in...
  19. duke37

    Audio Preamplifier produces glitches (cracks)

    I have had a thought on how a slow meter can see a short, sharp negative transient. i have not tried it.
  20. duke37

    DC Controlled AC Load

    Looks like a good posibility. The components will need to be sized to suit.
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