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  1. duke37

    Suppressor Advice Needed

    Your original post is not completely clear. It implies that the power source is 24V and you need to limit at 30V. There is not much latitude here. You could chose a device with a limit halfway between these values. The nominal voltage is included in the device number. RS have some 28.2V...
  2. duke37

    Suppressor Advice Needed

    A zener could be used, either on its own or to turn on a power device such as a large transistor or SCR. There are however Transient Voltage Suppressors designed for just this purpose. A fuse in the input line will limit the time the suppressor needs to act if the transient is not very short.
  3. duke37

    WACOM PTZ-630 overheat=plastic housing on Mitsubishi chip

    That looks like a very dead cpu due to overheating.
  4. duke37

    Unsure of how current works with two voltage regulators

    The 7805 regulators step down voltage to give 5V. The 7805 consume very little current (about 5mA) so if each regulator is sending out 350mA the total input current would be 710mA. Basically, current in = current out just as water into a pipe = water out less a little bit of leakage...
  5. duke37

    Fusible resistor identification

    This may be a resistor, check with a meter for resistance. Brown 1 Black zero Brown 1 (Number of zeros) Silver +/- 10% So this could be a 100 ohm resistor. If a thermal fuse, 100deg C or perhaps a 100mA fuse. A picture would help.
  6. duke37

    transformer observation

    I would be prepared to travel to a station on the Derby/St Pancras line and bring my Peak inductance meter to measure the parameters. This could be done on the station and I could be home for lunch (got to get my priorities right).
  7. duke37

    Switch Arc Suppresion

    I suggest that no components are put across the switch. If they fail, power could stay on the dryer. You can get voltage dependant resistors which will clip the very high induced voltages if placed across the dryer supply after the switch. Some extension leads have these in as protection for...
  8. duke37

    Need help with my Plant watering watcher circuit

    The led needs about 3V to turn it on. If you have a 3V supply and 0.2V dropped across a transistor, you have nothing to spare to drop across the resistor. If you go up to 5V supply, you will get about 1.8V across the resistor. With a 100 ohm resistor the led will take 18mA, which is OK
  9. duke37

    weird question... i think

    Yagi antennae usually have a loop radiating element which is close to a short at low frequencies, Bye bye amp.
  10. duke37

    TARDIS Console Project

    A switch would be needed, microswitches are good for this type of application. Many microswitches are not micro! They have a little buttom on the side to switch them and are normally fitted with a lever to allow it to be switched with a low force. Draw a diagram of the mechanical arrangement.
  11. duke37

    Trying to manipulate voltage

    Plot a graph of output voltage required versus input voltage.
  12. duke37

    Need help with my Plant watering watcher circuit

    Yes, IC1A is an oscillator with a frequency of 2.7/(R*C). The probe shorts out the signal when the conductivity is high. IC1D is another much slower oscillator to flash the led. It is modified to be asymmetric by using two feedback resistors, one connected through a diode. There are many...
  13. duke37

    50-300 uH adjustable coils?

    Yes, L1 should be similar to L2 and L3 to L4, one of each must be adjusable to match the other taking into account circuit variations. Any small signal npn and pnp trnasistor should do. Probably the ancient 2N3819 would do for the fets. PS We had a demonstration of a theremin at school...
  14. duke37

    Need help with my Plant watering watcher circuit

    The 4093 can operate up to 18V so 5V is OK as long as the resistor in series with the led is increased to limit the led current to an acceptable value. The link gives an explanation of how the circuit works, what particular part do you not understand? Have you built it or just tried to...
  15. duke37

    transformer observation

    I have followed this thread with interest, there has been much talk and little data. As far as I can make out, the experiments were done at 10kHz input to primarys of unknown number of turns on an unspecified ferrite core. The way to go would be 1. To measure the primary resistance and...
  16. duke37

    Trying to manipulate voltage

    Please give a block diagram of what you want. Transistors will switch in less than a millisecond so no problem there. A transistor can only switch one signal so you will need three switches. A silicon npn transistor will not be able to switch less than 0.2V so switching millivolts is not on...
  17. duke37

    50-300 uH adjustable coils?

    Looking at the circuit, it appears that there two oscilaltors which beat to produce the note and another oscillator which can sweep towards a tuned cicuit to give the volume. As such, this very wide range of adjustment is not necessary, thus in the case of the note generator the two inductors...
  18. duke37

    Cold Showers.

    In the UK electric immersion heaters are sometimes used for heating shower water. A typical power of 7kW (30A) is used with a dedicated high current supply. Water and electricity don't mix, or mix too well!
  19. duke37

    higher output MOSFET

    Its me again! I have driven mosfets with 10V, that has always seemed to be adequate at low frequencies. The driver here is supplied with 6V, is this enough to turn the fet fully on? The TC1412N can be stand up to 16V, a few more volts should bump up the current a bit. G3VLF
  20. duke37

    higher output MOSFET

    I have not used mosfets at high frequencies but the problem seems to be charging and discharging the input capacitance. The input capacitance changes during the cycle. Options 1. Use a bigger driver or more than one in parallel. 2. Use a smaller fet with lower capacitance. 3. Add some...
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