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  1. dorke

    RS422 to RS232 converter.

    I see a few things: 1. RS422 needs no return ground,it should be disconnected. 2. Put termination resistors as close as possible to the IC -pins(shortest legs). 3. Use a de-coupling cap ,as close as possible to the pins(shortest legs). 4. Use twisted pair wires for the RS422 lines. 5. Why the...
  2. dorke

    RS422 to RS232 converter.

    Well, You need to use twisted pair(you can twist them yourself for short distance). Use a termination resistor between A- and A+ same for B,value should be about 100 ohm. waiting to see schematics and photo.
  3. dorke

    Hacking the buzzerbox

    Let's start from the end. As I said it is a powerless unit. Number 2 isn't a source of power(D.C), it is part of the audio circuit (A.C). You can try to find D.C voltages between all pins combinations while no button is pressed(using the DMM in DCV range),I guess there are non. If by "the...
  4. dorke

    RS422 to RS232 converter.

    That shouldn't be like that ! When you say "disconnect" ,what exactly do you do? Where do you disconnect? Are you using line termination? Are you using twisted pairs? What length are the wires? Please show schematics and photos of the board and connection.
  5. dorke

    Hacking the buzzerbox

    This "suite station " is a powerless unit. The speaker function was correctly described by @Tha fios agaibh above. On the photo of the board you have "+SP" marked,that is the plus of the speaker Number 2 is the audio common-the only un-switched connection, connected permanently to +SP...
  6. dorke

    After the Transformer Help

    Welcome to EP. The best thing for you to do before you do anything ,is learn the basics. Your own words speak volume of lack of any knowledge,unfortunately, this is very common here :( We do try to help,but in some cases ,the best advise is stop before you harm yourself or cause damage...
  7. dorke

    Anyone bought from "futurlec"? good source?

    I need some Japanese obsolete Trs for an old Fisher receiver : 2SC708A,2SA537A,2SC1030. All claimed "brand new" are probably fakes ,"pulled" are shamelessly expansive. Probably need equivalent replacements from a reasonably source. It is those analog parts they love to fake, If I get fakes it...
  8. dorke

    Anyone bought from "futurlec"? good source?

    Thanks Steve, Did you buy transistors(especially high-voltage 100V or more ) from them? where they genuine parts?
  9. dorke

    Anyone bought from "futurlec"? good source?

    If you did buy from them,would like to have your review/opinion : Reliable? Genuine parts? Prices? Shipping price and time ? etc. http://www.futurlec.com/Transistors.shtml
  10. dorke

    Casio PT80 Keyboard - suspected transistor failure

    From the photo The TR. The legs are dirty,could be from the un-soldering,but I think not,it is typical of old equipment It is hard to see If there is the same kind of dirt on the body between the legs. It should be scraped well(gently) with an exacto knife and cleaned with rubbing alcohol...
  11. dorke

    Casio PT80 Keyboard - suspected transistor failure

    That is basically a toy not a real quality keyboard. May be the PT stands for Play Toy ;) Anyways, The way an analog synthesizer works is much more complicated than suggested above. It involves analog signal processing not merely a chain of amplifiers (varies filters,mixers,wave shaping ,and...
  12. dorke

    Very Bad EMI

    Let me add: 1. Your μC U1 is missing de-coupling caps with shortest legs possible,this may be critical. 2. Try a smaller pull-up on U1 Pin-4(functions as MCLR) say 1k with shortest legs possible. 3. show a photo of your actual build of the circuit. 4. A DSO may help you find the source of the...
  13. dorke

    Convert waveform formula to 'usual' cos sin formula to sketch graph

    This may help you (from wiki): There is no "D=Vertical Shift" here,but it can be easily added if needed. We call it the "DC part", i.e zero frequency part.
  14. dorke

    Phasors and Phase angles

    Welcome to EP. The "phase shift" is indeed relative,for a single source driven circuit you may take the source to be at 0 phase. The phase angle is dependent on the ratio of the reactive (imaginary,"j part") to the pure ohmic (real part) of the impedance of a circuit or a branch of it. We...
  15. dorke

    Casio PT80 Keyboard - suspected transistor failure

    An audio signal tracer can be home made easily and cheaply in many ways. You can use cheap magnified speaker(s),or small battery powered speakers etc. (you may have them laying around without use anyways,or you can build one from scratch) . All you need to add is a blocking capacitor and make a...
  16. dorke

    Casio PT80 Keyboard - suspected transistor failure

    I actually wanted the photo of transistor itself from the leg side. The purpose is making sure there is no dirt/corrosion on and between the legs.
  17. dorke

    Wanted: Oscilloscope help

    For 1 and 3 you actually need a logic analyzer with protocol interpretation. The speed of has to be determined by tour application speeds. A scope is needed for 2 ,it's parameters should be determined by your bandwidth and frequencies. 2 or 4 channels? 4 is better but more expansive, though...
  18. dorke

    serial interfacing

    Mr. rivizi, You must have very good karma...;) Read and implement this (pages 161 till 181),do report back if it works.
  19. dorke

    serial interfacing

    Yes absolutely,it may be easier done in a DOS environment. The program (and programmer) needs complete access to all com. port lines... And the knowledge of how to do that;)
  20. dorke

    serial interfacing

    Because the MAX187 doesn't talk "rs232" ! There are not used as handshake, rather they "toggle" the "command" lines of the MAX187 and read, bit by bit ,it's output.
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