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  1. Alec_t

    Morse code led without a micro controller

    Or you could do the cheat version with 1 IC, like this :- U1a is the basic oscillator which operates at one of two frequencies depending on whether Q2 is switched on or not. When Q1 and Q2 are on, the U1a pulses are integrated on cap C2. When U1b upper threshold is reached (3 short pulses...
  2. Alec_t

    Trying to get this circuit to work on breadboard

    With only 100Ω series resistance your transmitter LED will be passing about 70mA if the battery is fresh. Is the LED rated for that much current? If not, it won't last long.
  3. Alec_t

    Odd Behavior of Circuit

    Try connecting a fat cap, say at least 100uF electrolytic (correctly polarised), 25V rated, in parallel with a 100nF ceramic cap, across the bell terminals.
  4. Alec_t

    HP DeskJet 5550 suddenly gone into Very Slow Printing Mode

    Welcome to EP! Are you trying to print larger files than before the problem arose?
  5. Alec_t

    Digital transistor for switching application

    You could do that, but it would be more complicated because the NPN base would need an input (control) voltage 0.6V or so above the voltage you are trying to switch. That, in turn, would need a second supply.
  6. Alec_t

    Multi turn potentiometer insted of regular

    Providing the resistance and current-handling ability of the new pots are the same as the existing ones it should be ok.
  7. Alec_t

    Pipestat query

    Glad you've got it sorted.
  8. Alec_t

    Solar powered fan

    I can't see a timed delay being useful, given the variability of sunlight. Duke's suggestion to control the fans on a temperature basis seems a better bet. What are you going to do with the heat you collect?
  9. Alec_t

    Pipestat query

    True, but as I understand it (if this thread relates to a previous one of his), the TS is not using mains voltage; just a 12V supply on a boat. Perhaps he can enlighten us?
  10. Alec_t

    DC power supply with different V out

    You could try this switch-selectable output regulator :- The P-MOSFET (M1) should preferably be a logic-level type. Rload is just a simulated load. C1 suppresses noise on the output. Almost any comparator could be used instead of the LM339 (a quad package, only a quarter of which is used...
  11. Alec_t

    Pipestat query

    One option would be to use the existing stat to switch the coil of a standard automotive relay or similar. Such a relay has a relatively low coil current well within the stat's rating and its contacts are designed for relatively high DC currents (check the datasheet). Or for a solid-state option...
  12. Alec_t

    Pipestat query

    I don't see any DC current rating in the datasheet for your stat? Methinks you could get contact arcing/welding :(.
  13. Alec_t

    Can you make my 12v LED light up?

    No offense taken. Not everyone knows Wales is in the UK :D.
  14. Alec_t

    Pipestat query

    That may not be possible with a simple mechanical thermostat, which will have ~ a degree or two of hysteresis between the turn on and turn off temperatures. The purpose of the accelerating resistor is to help minimise the hysteresis. Hysteresis is generally desirable, to avoid the pump cycling...
  15. Alec_t

    Driving an electromagnetic passive SMD buzzer

    So why do you need a regulator?
  16. Alec_t

    Fm transmitter data pins, what are they for?

    Hopefully not, if it's interfering with other people's FM reception :).
  17. Alec_t

    Transformer primaries in series, secondaries in parallel -- ok?

    If P1 and P2 are the respective primary coils of T1 and T2 then they need to be in series in order to get 15V out from the secondaries.
  18. Alec_t

    Audio tone generator

    You're aware that Variacs are auto-transformers, hence don't provide mains isolation?
  19. Alec_t

    Display for 3D printer

    Is an LCD capable of blocking the fairly high levels of UV which you'll possibly need for 3D printing?
  20. Alec_t

    Odd Behavior of Circuit

    If the hefty bell is a good olde-fashioned solenoid type then the coil inductance kick-back spike may be causing havoc. Do you have a reverse-biased protection diode across it? Edit: Kelly beat me to it!
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