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  1. duke37

    LED Project help, please?

    You can mix the colours but if you make a mixed string first you can check on the relative brighness. 20mA is the normal maximum current but you may wish to reduce this if one colour is much brighter than the other. Obviously, the current is the same throughout the string. You could get 3...
  2. duke37

    LED Project help, please?

    I think you should decide on the battery first. If the leds are to be switched on and off together then the circuit will be simpler than if they are to be sequenced. To run from 12V, you will need to have several strings connected in parallel. Each string should have several leds in series...
  3. duke37

    LED Project help, please?

    121 leds at 20mA is about 2.5A if run in parallel. What battery do you suggest?
  4. duke37

    Simple Amplifier

    The Droitwich transmitter takes a sine wave signal and gives 200kW out. Is this sufficient or is your max more than this?
  5. duke37

    1.2KW RF Detector Impedance?

    Do not do it. If you do not know what you are doing, you are putting yourself into extreme danger. You have not given details on the equipment or your capability.
  6. duke37

    Quad Comparator Help

    The comparator can work with inputs down to the negative line but I see no information as to how high they can go. I suspect that you are trying to run the inputs outside their range. The inputs should be a bridge so that one input is at half the battery voltage (use two equal resistors) and...
  7. duke37

    Quad Comparator Help

    The LM339N contains four comparators with open collector outputs. To determine the output, one input has to be higher than the other. You say there is 8.3V on both inputs but one will be higher than the other. What is the power supply to the comparator? What are the actual accurate voltages...
  8. duke37

    Connecting capacitor and Diode

    Give us the complete circuit and we might be able to answer.
  9. duke37

    Quad Comparator Help

    What is the comparator that you are using and what is the circuit? Comparators often do not have the facility to pull up the output. They need to have a resistor from output to Vcc.
  10. duke37

    Need help for simple LED circuit

    The dissipation in a resistor is current times voltage across it. In the first case of 20mA and 21V, the dissipation is 0.42W so a half watt resistor would do but I would put in a 1W, the bigger resistor would run cooler. In the second case 20mA and 4V, the dissipation is 0.08W so any diddy...
  11. duke37

    Powering a washing machine solenoid?

    You can get invertors to run on 12V and give out 50Hz AC (UK). You can get boost convertors to give out higher voltage DC You can make a boost convertor with a few components a chip and a couple of fets. The transformer will be the problem. I use old cores from TV line output transformers but...
  12. duke37

    Need help for simple LED circuit

    You can use a resistor in series with the led. If you could pass 20mA, this is the normal current for a low power led, then subtract the led voltage from 24, then multiply this figure by 50 to get the resistor value. With a 3V led, 21*50 = 1050, use 1k. Note that with 24V you have sufficient...
  13. duke37

    Powering a washing machine solenoid?

    You can power an AC solenoid with DC and in fact, you will need less voltage, perhaps half the AC value. You can dismantle the solenoid if you have a big enough hammer and rewind with fewer turns of thicker wire to use a lower voltage.. You could get a solenoid to run off 12V.
  14. duke37

    Questions about MOSFETs

    Mosfets are often used as switches since they can have a very low resistance when turned on fully. If they are not fully turned on, they can be used to amplify signals like other transistors. They need negligible current to turn them on or off, the input is more like a capacitor. There are...
  15. duke37

    Westinghouse SCR 44TB2

    There are different stud diameters and they may have UNF or metric thread. They do not usually come with a matching nut. Looking in a very old RS catalog, the bigger SCRs have a 1/2 inch-20 UNF stud.
  16. duke37

    Westinghouse SCR 44TB2

    The 44TB2 SCR appears to be a 200V 70A device. I do not see what package it is in. If it is running at a high current, then it will need to be fitted properly into a heat sink. It depends on which country you are in for the best place to look for a replacement, in the UK. RS CPC Farnell...
  17. duke37

    Voltage Regulator Question

    You cannot get 12V output from 12V input even with a low drop out regulator. I do not know the best type of capacitor but they should be placed close to the regulator to limit lead inductance. They are there to stop oscillation.
  18. duke37

    Car Water Temperature Sensor

    Thanks for the replies. The meter is a thermal meter, working on PWM with pulses at about one/second. Debe has posted a picture of a similar meter showing the heater wound round a bimetallic strip. The 12V goes through the 25R meter and then through the 25R switching sensor to chassis...
  19. duke37

    Voltage Regulator Question

    The 555 can be run down to 5V. I suggest that you provide it with a regulated supply of 8V and use it to drive a transistor to suit the load.
  20. duke37

    Circuit design help

    The microwave transformers I have seen have a common connection for primary and secondary i.e. they are not isolated. I am not into very high voltages, 1kV is enough for me. My microwave oven needs repair but I will not do it. There are people who like high voltage sparks, they use Tesla...
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