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  1. majoco

    How to design a transistor circuit that controls low-power devices

    I don't know why this has turned out to be so difficult. Here is a simple schematic that I designed to run a small computer fan from a temperature sensor on the top of my Marantz tuner/amplifier - the fan gets a linear voltage to drive it from the sensor stuck on the top of the cabinet, the fan...
  2. majoco

    Basic Pulse generation help

    What's the point in repeating two old threads that supposedly everyone has read with making any comment?
  3. majoco

    Assistance in decoding a circuit diagram

    The reason for the two pins connected together and to the adjuster of your variable capacitor is to ground the adjuster - those two pins should be the ground connections - this prevent the tool you are using to turn the vanes affecting the capacitance. Also foil wound fixed capacitors often...
  4. majoco

    Basic Pulse generation help

    Now there's interesting...... ALT codes! ALT928 prints as capital pi in some scripts, ALT960 prints a lower case pi, but not on this forum screen! Also found that ALT937 print a nice 'ohms' omega!
  5. majoco

    Basic Pulse generation help

    You're right! Brain fade! I used pi.2D - should have thought pi.D. The end result is the frequencies are doubled, 100mph = 84Hz, 10mph = 8.4Hz - apologies to all.
  6. majoco

    Basic Pulse generation help

    Well, we don't know! In the sketch of the square wave it looks like the mark is slightly shorter than the space and as it's probably a mechanical magnetic pickup I guess that the M/S ratio will stay about the same even though the frequency will change, 4.2 Hz at 10mph and 42 Hz at 100mph! A...
  7. majoco

    Basic Pulse generation help

    Interesting exercise - I did it a couple of times as it didn't look right. I just measured my "17 inch" wheel and its just over 26 inches diameter which makes it 163 inches circumference, 13.6 feet. and so 5280/13.6 = 388 revolutions per mile, 38,800 revs per 100 miles, 38,800/3600 = 10.7 revs...
  8. majoco

    For Sale: Have lots of vintage electronics to sale. What is best web page or site to do this on.

    IMHO I'd look at www.https://antiqueradios.com/ You'll probably have to register as a member and there's a stand-down period. You haven't said where you live - I think they only operate in the USofA. Ebay will get you the most exposure but probably the lowest bids! Just make sure you get the...
  9. majoco

    How to design a transistor circuit that controls low-power devices

    One problem with electronics is the need for correct description, especially when dealing with values that range from pico (10 to the -12) right up to Meg (10^6). If I did some sums on a circuit and found I needed a 200 watt resistor, I'd do the sums again!. It's a 200 ohm resistor, 180 ohms is...
  10. majoco

    CRT

    A shop near me that mainly sells to offices etc sells off old equipment for a pittance - office equipment is a tax write-off after some three years or so - the shop has monitors, printers, bricks for not much more than NZ$25 if you talk to the receptionist nicely!
  11. majoco

    Crystal oscillator 15pF load

    IMHO the load affects the waveform - 50ohms load makes the output into s a sine wave, 15pF might preserve a square wave shape. As in most things - one test is worth a thousand opinions. ;)
  12. majoco

    Basic Pulse generation help

    From the pulse generator specs.... So 12volts Vcc in will give 11.4volts p-to-p signal - I see no problem.
  13. majoco

    10.7 MHz oscillator with transistor

    VHF FM IF amplifiers need a bandwidth of about 180kHz (as shown on that MuRata pic) so how do we know where in that 180kHz the thing is oscillating?
  14. majoco

    Ring Doorbell & Bosch Wifi Thermostat issues

    From this: ...I suspect that it's not the thermostat and it's WiFi transmitter at fault, it's the device you are using to pick up the WiFi signal as it is not picking up any of the signals that were there originally, not just your thermostat signal.
  15. majoco

    Basic Pulse generation help

    I wouldn't get too worried about the "output pulse generation" at the moment. See if you can get the speedo part working first. A "Function Generator" can do all that you need as far as generating signals is concerned. I suspect that the signal coming from the wheel speed sensor is not a nice...
  16. majoco

    Light bulbs as dummy load for Stereo ?

    A 10ohm 5watt resistor is probably cheaper than a lamp.
  17. majoco

    Simple SW receiver on 3V?

    Try again.... theradioboard.com/rb/viewtopic.php?t=4554 ...scroll right down to the schematic.. ..
  18. majoco

    6v LED brighter with 3v battery

    Story. A few (no, many!) years ago, we had an aircraft come in to the hangar with a pilot written-up defect "Port engine fuel pump fail". So the airframe engineers drained the fuel collector tank, removed the pump, replaced with new one from stores, test and still didn't run. Measure voltage at...
  19. majoco

    CAR LED headlight - load resistor (aka "CANBUS")

    Parallel???? Why parallel??? all you're doing is draining the battery. LED's like a constant current source, not a constant voltage. A car battery is NOT constant voltage - running down the road with a fully charged battery with an alternator charging, the battery can easily get up to 16volts...
  20. majoco

    finding 4 pin connectors for own wires

    Just gooooogle for "Molex" connectors, just like the ones that were used for powering hard drives..... :)
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