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  1. audioguru2

    4W FM Transmitter

    The one on the left works fine. The one on the right doesn't work because its long wires have too much inductance and stray capacitance for it to work at the Very High Frequency of about 100MHz. T1 is the main oscillator. It and its associated parts must have short wires.  ;D
  2. audioguru2

    perfboards

    Hi Cody, I use a copy of Veroboard, also called stripboard. It has printed strips of copper paths in one direction that are cut with a knife or drill-bit. Half of a pcb is already done and the components and some jumper wires make the rest of the wiring. It is perf board so the holes are already...
  3. audioguru2

    Solder Fumes

    Hi Cody, My soldering iron is temperature controlled and doesn't turn the rosin in the solder to smoke, just pleasant smelling steam. The steam rises in front of me, not into my face. I also seem to hold my breath when soldering, so my hands are steadier. I huff and puff a bit beween joints...
  4. audioguru2

    4W FM Transmitter

    Which pic looks like your component layout?
  5. audioguru2

    4W FM Transmitter

    Hi Radiopirate, The case of the transistor is connected to its collector. The stray capacitance of the heatsink to its surroundings kills high frequencies at the transistor's collector. Can you peak the output with the trimmer capacitors? If they run off the end of their adjustment then their...
  6. audioguru2

    OPTOCOUPLERS

    The optocoupler has a single LED and a single phototransistor. The chain of transistors amplify the current output and voltage rating of the phototransistor.
  7. audioguru2

    4W FM Transmitter

    Hi Platonas, Q1 will dissipate about 750mW in this circuit. Little transistors like BSX20, 2N2222 and 2N3904 can't dissipate so much power without melting.
  8. audioguru2

    OPTOCOUPLERS

    Oh yeah? Do you think that the tiny phototransistor in an optocoupler switches the entire load all by itself? Duh!  :o ::) Firstly, the LED in a optocoupler has a max current rating of about 60mA. Secondly, the optocoupling isn't perfect so the phototransistor can conduct only about 40mA when...
  9. audioguru2

    OPTOCOUPLERS

    Optocouplers provide isolation. They use a light beam for coupling instead of conductors.
  10. audioguru2

    Very Upset with Size Limits.

    We party every night but not together!  ;D
  11. audioguru2

    HV power supply

    There are some neon sign transformers on the windowsill of a store near me. They are the size of 2 bricks and are rated at 12,000VAC at 20mA. Their mains and HV terminals are exposed bolts, kinda dangerous with kids running around in the store.
  12. audioguru2

    Re: Alun's low voltage alarm

    Hi Alun, Nobody could wait for the phase of the moon and the season to be correct for Low-Power comparators to give any output current. So they started using transistor buffers with them like you. They also didn't use or buy the strong ones which became extinct.  ;D
  13. audioguru2

    Bias temperature sensor?

    Hi Mphotis, Connect it like this. Do you have a differential input to feed its outputs to?
  14. audioguru2

    Re: Alun's low voltage alarm

    A really strong LM339 would provide 20mA into a dead short and about 16mA with a 1.5V saturation loss. A weak one will provide only 6mA with a 1.5V saturation loss. Even less if it heats up. You might be unlucky if some of the weak ones are sent to your country like they send to mine. It's...
  15. audioguru2

    lm339 comparator

    Hi Joe, You almost understand the operation of an LM339. Since the output is only the collector of an NPN transistor, the output becomes open-circuit (and is pulled high by an external resistor) when its + input is more positive than its - input. When its - input is more positive than its +...
  16. audioguru2

    Re: Alun's low voltage alarm

    Hi Alun, Your boss told you to use a 5V regulator to power a chip with a 5V to 15V rating, so it isn't damaged and doesn't become unreliable when the 15V supply is high. It's a voltage reduction that's too extreme. Will the chip even work if the 5V is actually 4.8V? Did you notice the typo...
  17. audioguru2

    Bias temperature sensor?

    Hi Mphotis, The circuit is on the 1st page of its datasheet. http://www.national.com/ds.cgi/LM/LM35.pdf If you need a different output voltage range or offset voltage, use an opamp on its output.  ;D
  18. audioguru2

    Transducer digital output to analogue

    Hi John, If you need any accuracy of the pressure switch-point, use a comparator IC instead of a transistor. Also use a 10:1 resistor ratio in the differential amplifier opamp to boost the 330mV of the transducer up to 3.3V for the comparator. The reference voltage for the comparator will be...
  19. audioguru2

    pcb layout for electronic stethoscope

    I can't open its "pcb" extension in Paint and I can't change it to "jpg" or "bmp" or "gif". The circuit has only 2 or 3 small ICs. Why not make it quickly on Veroboard like this other project?
  20. audioguru2

    4W FM Transmitter

    Farnell is in at least 23 countries including Australia. I clicked on your flag and went here: http://au.farnell.com/jsp/home/homepage.jsp They don't have any 2N2219 transistors because their supplier doesn't make it anymore. They have thousands here in Canada. They don't have a 2N3866...
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