Search results

Search Forums New Posts
  1. duke37

    Simple inverter

    You will need a transformer. You could try taking the output from half the primary winding. The voltage will be low but may be enough. Taking the output from the whole primary will give a high voltage which could be tamed with a series resistor. The original primary would not be used.
  2. duke37

    Questions regarding capacitors

    I have no idea how I came up with 2.53 either, perhaps my brain cell is getting discharged! 1000uF capacitors will have a lower series resistance than 10uf caps. I intend to build an ESR meter this winter. If the load resistance is equal to the internal resistance, you will get maximum...
  3. duke37

    not exactly an electronics repair.. need advice

    Before dismantling, check the resistance across the input wires, it should be a few ohms. If it is open circuit, check the resistance across the bass speaker, it should be a few ohms (same as input). If you have a stereo pair, compare the two. Measure the resistance across the inductor, it...
  4. duke37

    Questions regarding capacitors

    I could not find the page quoted. Some sums, they should be checked! 10microF 230V Energy = (C * V * V)/2 = 2.53J 52kW = 52000 J/sec Time for constant power = 2.53/52000 = 48microsec Therefore I cannot see how this works. In practise, there will be a resistance in the capacitor in...
  5. duke37

    help with adjustable power supply

    The common rail or ground is the lower wire on the circuit diagram. If you can measure a voltage between V+ out and V- in but not between V+ out and V- out, then there is no connection at some point on this rail. Check with power off, the resistance between - in and - out.
  6. duke37

    help with adjustable power supply

    It looks as if everything is working as it shoud except that the transformer common and output common are not connected. The 317T regulates to give 1.24V between output and reference input and this is what you get when the pot is at zero ohms. With 12V input, you will not get much above...
  7. duke37

    How to use Piezo Electric Tape?

    Have a look at "charge amplifiers" in Wikipedia. You should use a fet input op-amp. The sensor only gives an output when the input changes, you will probably need a rectifier after the op-amp in order to get a reasonably steady signal for the computer to read.
  8. duke37

    555 sequential timer circuit

    You are right about the resistors, my thought was a good way of zapping the leds!
  9. duke37

    555 sequential timer circuit

    The 4V drop on the TIP122 will be there if supplying 4A, your relays presumably take much less than this. Do you need a relay? I was under the impression that you would be driving the solenoids directly. A little simplication can be made by using a single 470R resistor to feed the common...
  10. duke37

    timer switch

    60 seconds is on the verge of practicality for a RC timing circuit but perhaps could be done if timing accuracy is not the issue. You would need a high value resistor and a very low leakage capacitor feeding a Schmitt trigger (4093) and a double pole output relay. For long times, an...
  11. duke37

    I need help with my first flyback converter

    Most power supplies are happy when feeding an open circuit and do not like a short circuit. The switch mode supply that you have is the opposite of this, it is happy running into a short circuit and does not like an open circuit. You should therefore always use a load to provide somewhere for...
  12. duke37

    Garage door open switch to Honeywell thermostat

    Welcome to the forum. Reed switches are somewhat delicate, I would think it better to use a microswitch. The standard switch can manage 5A at 250V AC.
  13. duke37

    Converting from AA to Li-Ion

    If you want 3V and have a 3.7V battery, just put it through a silicon diode which will drop about 0.7V
  14. duke37

    555 sequential timer circuit

    Yes, if you lose 4V in the switch, you will only get 8V in your load. The equivalent connections as you say are:- Base = Gate Source = Emitter Drain = Collector 12v is good to turn the fet fully on so connect it to the output of the 555 without a voltage divider. A gate resistor of...
  15. duke37

    555 sequential timer circuit

    The data sheet says drive with 20mA to provide 5A. The drop across the transistor will be 4V so there will be 20W dissipated - a lot. An IRF540 fet will have resistance of less than 0.1 ohm when turned fully on, so loss = 5 * 5 * 0.1 = 2.5W The catching diode must be connected across the...
  16. duke37

    555 sequential timer circuit

    Comments 1. The 4V maximum on the transistor I think is the maximum b-e voltage with the base negative. This will not apply here. 2. The transistor needs a specific input current, this can be obtained with a single resistor from the 555. 3. A junction transistor will drop a volt or two...
  17. duke37

    Wireless Distance Proportional Signal Circuit Help

    A1 and A2 can send a signal alternately. B does not need to know where this signal comes from, it just has to respond quickly. Both A1 and A2 will need connecting to an analysing system to calculate position. Note that there will be two possible positions, one in front of the line A1 to A2...
  18. duke37

    explain me the the basic of transmitter and receiver

    It is the on/off switch.
  19. duke37

    bridge rectifier project

    If you rectify an AC signal and feed it into a capacitor, you get Vrms * 1.414. If you feed into an inductor, you get Vrms * 0.9. Thus remove the capacitor and there may be sufficient inductance in the motor to make the supply look like 120 * 0.9 = 108, only a little bit high.
  20. duke37

    Use Electromagnetic energy to crush a aluminium can?

    Be very careful as Dave says. Presumably all the capacitors are the same and polarised, tell us what they are. There will be a very big current inrush when connected to the mains, you will need to fit a current limiting resistor. There will be a very large outrush of current when the...
View older results
Top