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Posts posted by trigger

  1. AM demodulation is envelope detecter only.
    And the loudness is depends on the modulation depth of the source.

    And IF is the resultant frequency of the difference between the local oscillator and the carrier frequncy, which is to lower the frequency for demodulation.

  2. there are thousands of factories in china.....
    some of them are qualified manufacturers of those large brand names, where they will have a better qualifty control + ISO certificate.

    some don't have anythings.... mostly these only supply to china local stores.....

    somhow these un-qualified products may leak out to other countries.......

    thus.... I prefer a brand name one in a proper local stores

  3. first, you got to know it is a common anode or common cathod 7 segment LED display.

    second, the fastest way to check the a, b, c...g is to directly check which pin will lit its corresponding segment by applying power across the pin and the common terminal.

    Remember, test is always the fastest way rather than asking, especially there are many specification on 7 segments LEDs.

  4. audioguru,

    Your project is great, save me from thinking on how to flash a bunch of LEDs with 2 AA cells...
    I will build my own too, not for $$$, but for a special gift to my girlfriend..... ;D

    The IC with prefix CD40xx may not work at 3V but the 74HC40xx should be work fine with 3V..... I gotta check this out.

    Anyway thanks!! ;D

  5. No offend here but I want to tell some facts.

    Shenzhen, a city in South China near Hong Kong, got very cheap components since many factories around. And there is a shopping mall that have many many shops to sell components in very low price.

    Imagine just needed USD$2.5, you can get 1K pieces of SMT resistors (a tape).

    If I start business in Hong Kong and have sent components to US or around the world, I am rich ...... :P

  6. not just east copy west.... but also some US fabless will copy and improve the chips.

    One example is california microdevice (hmm... hope I haven't mistaken) .... they have single opamp with low noise and wide bandwidth which is pin to pin compatible with NS one..... but I forget the part number......

    And that single opamp is used in an AGC video circuit with very fine performance....... even better the original one......

  7. audioguru,

    May be you are National semiconductor supporter, but I am not.
    Mostly used in products will no longer be NS brand, but some others.
    Check the link here:


    Check what the specification on KIA358 and KIA324..... compared with what you found in NS. You will noticed what actually I mean previously. These ICs are pin to pin compatible with better specification.

    And of course I know LM324 is quad version of LM358, don't just treat me as a fresh graduate..... :P

  8. I can tell, LM324 used as audio amp is much worst than using LM358.
    As circuit designer, we always like to use the perfect components.. however, the reality will not let you to, esp. your boss is barking loud to stop you.

    And I can tell, some of those opamp, are now produced by Korean or taiwan (some even china); some of them, also being modified by US fabless company with better specification.

    So in some case, the chip is always improving rather than continuous with their noisy specificaiton.

  9. some of the opamp are crap but that doesn't mean it is not suitable for products.
    I can tell, LM358 is still widely used in many everyday products..... why, because it is low cost....... (the price of IC is not what you seen in the local store)
    Actully, no manufacturers will care about the noise and distortion but price.....

  10. thanks Suraj,

    But those programmers are using parallel port instead of serial port.
    I also come to some parallel-to-I2C circuits, with complete source code.
    May be I have to use an MCU to translate the serial data to I2C/SPI.
    Anyway, thanks for advice.
    I will post something out once I got some progress.

  11. Hey Oilhou,

    I am same as you, come from Hong Kong. ;D
    There are some places where you can buy components, like in Sham Shui Po Ap liu Street, IC master in ShanPoKwong, Leader in Kwun Tong, etc.
    If you can't get required components, you can try local RS or Fernell, there you should get some..... but expensive.
    Or you can go to Shenzhen for components..... but less reliable...

    Hope this can help.

    Dear Audioguru

    I am in a small place south of China, ruled by British for one hundred years until 1997 when it is returned to China. Got it? ;)

    I have been searching for the inamps. They are available locally only in large quantities! So I am still thinking if I can use opamps readily available, as you have suggested. However I find opamps, such as TL074, LM741 or LM709 are normally of low CMRR, around 20 to 30 DB lower than the inamps. Besides, to build inamps from these opamps, high matching resistors (specified to .1% in circuits I have seen) are needed. No easy job to me!

    Or you can advise me where to get the inamps. I will be prepared to buy just two to three pieces, as they seem to be very expensive.

    One more question for your help please. For the INA118 circuit I have posted previously, I do not quite understand what is the purpose of the amplifier output of which is connected via a 390 Kohm resistor to the right leg. Also why the gain is made to 39 (390k over 10 kohm)? Do you have a good explanation?

    The links you have provided to other discussion forum are very useful to me.

    Thanks and best regards


    from Hong Kong

  12. Ante,

    I have come to such problem yesterday.... and found the loading on the pages were quite slow....... and then turn out the error pages as shown. But try reloading pages seem to cure the problem.
    Today there is no more such problem and all are working fine, included the "new" button.... so you better check with Mixos....


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