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  1. duke37

    Crude Variable Inductor / Transformer

    Yes, that is the idea. I saw somewhere that modern variacs used carbon fiber brushes to do the same job but don't know if this is correct. My little variac came out of a skip and I fitted it with a 'brush' made from a 6B pencil. The roller transformer you show is interesting, are there two...
  2. duke37

    Crude Variable Inductor / Transformer

    As I remember, a Variac has a twin brush, glued together so that there is a resistance between one turn and the next. If a ball bearing were used, there would be a shorted turn when placed on two turns, resulting in a considerable amount of smoke.
  3. duke37

    Application of 7805

    1. The 7805 will limit output current to 1A so you will not get the current you anticipate. 2. The 7805 tries to raise the output voltage 5V above the reference terminal. The reference terminal is connected to the output so the output voltage will rise to about 2V below the input. 3. A high...
  4. duke37

    Voltage Regulator

    I think I would go for 100uf in parallel with 0.1uF on input and output but others may know better. A diode across the chip is often advocated so that a reverse voltage does not destroy it if the supply is disconnected and the device tries to power something else connected to the input...
  5. duke37

    Voltage Regulator

    Sorry, I meant to say 15V to 18V Zener diode to clip any high voltage spikes which can be generated in such systems where there are high current motors.
  6. duke37

    Wood for the Trees

    I am not familiar with synthesisers such as this but if the synth drifts from 1V/octave to some value, slightly different, couldn't a variable gain op-amp do the job? If the synth drifts but the octaves are correct, then a small voltage offset would be required. Is it polyphonic?
  7. duke37

    Voltage Regulator

    That looks good to me. You will need some capacitors across the input and output. A series resistor of about 18 ohms and a 15V to 18V across the input may protect from voltage spikes. 200mA would discharge a motor cycle battery quite a bit if left connected.
  8. duke37

    Battery used up

    A charged lead/acid battery will have one plate lead and the other plate lead oxide. They are immersed in sulphuric acid. When the battery is discharged, both plates are lead sulphate and the acid is very weak. A zinc/carbon battery has a case of zinc, when the battery is exhausted, the case...
  9. duke37

    Chat_Ghosty's PSU

    You are right, it is 230V, I know because it bites. I missed the 0 but I did find the caps key for V!
  10. duke37

    Chat_Ghosty's PSU

    Some switch mode supplies rectify the input with a bridge for 230V, giving 325V and use a voltage doubler for 110V, giving 311V. I was given one to repair after it was brought back into the UK and not switched to 23V!
  11. duke37

    solar

    Amorphous means non- crystalline.
  12. duke37

    MOSFET IRF540A circuit.

    I have not been following the thread and the Maplin site seems to be more annoying than usual this evening. The diodes you want are presumably 1N4004 and any diodes up to 1N4007 would do.
  13. duke37

    How can I drop 12V to about 8.4V?

    Use a LM317T regulator with a variable resistor to control the output. You should be able to set the voltage anywhere between 1.3V and 10V. There will be power loss so heat will be generated, you may need to heat sink the 317 if it gets hot to the touch.
  14. duke37

    Mysterious disintegrating 317s

    Should there be a capacitor across the variable resistor? This will slow the feedback and perhaps put the circuit into oscillation.
  15. duke37

    what power supply to buy?

    A scrap audio amplifier could give you +/- 30V and some of the components to provide voltage regulation and heat sinks. Current limitation should be included for experimental use.
  16. duke37

    Increase and decrease 0-10v output with momentary digital signal?

    Yes, you will need two comparators, one to isolate the up input when 1111 is reached and one to isolate the down input when 0000 is reached.. I have not studied the 4192 in detail but there are two cascade outputs which it may be possible to use.
  17. duke37

    Increase and decrease 0-10v output with momentary digital signal?

    The 4092 has one input for up and another for down, this makes it simple. If you are satisfied with pressing a switch once for each step, then things are even simpler. Should be 4192
  18. duke37

    Increase and decrease 0-10v output with momentary digital signal?

    The cmos 4192 is a decade up/down counter. You will need a pulse generator if you wish to the count to continue to change if the switch is held. The output will need a resistance ladder to sum 1,2,4,8.
  19. duke37

    Chronograph for bullets

    Could you make a rectagular frame and wind fine wire round it? The spacing can be as close as you wish, the double thichness may not be a problem.
  20. duke37

    Need Advice 110 to 24v

    The link goes to details of an AC transformer. You will need a DC power supply. Try to get the power requirements off the motor.
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