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  1. MP1

    Led display Digital Voltmeter question

    Gustavo, if you scroll up to page 1 of this thread, Billy has posted some corrections to the circuit. I have also found a board layout file with schematic both in Eagle format on the Eagle site that uses these parts and is very similar. It was donated by a user. If you do not have the Eagle...
  2. MP1

    metal detector

    It is highly unlikely that you will be able to do this. If it was sold as a toy, it will probably not use components that will allow you to tweak more sensitivity from the circuitry. You would literally be rebuilding the device. But that is only speculation on my part without being able to see...
  3. MP1

    Inside a TO-3 Transistor case

    It makes sense, since light absorption is a characteristic of silicon. I was just surprised that you could have enough surface space to get such a reading. Thanks for sharing that! MP
  4. MP1

    control RELE by parallel port of pc

    As Billy has stated, you will need resources for the software. It also depends upon the language you use. C does not do anything you do not tell it to do. Visual Basic sends an automatic line feed and new page unless you tell it not to. If you want to communicate to the outside world from...
  5. MP1

    Power supply for AMP in CAR

    Another way would be to take the power inverter diagram from the projects section of this site and modify it. I am referring to this project--> http://www.electronics-lab.com/projects/power/018/index.html Method 1: Instead of using a tansformer that steps the voltage up by 10, use one...
  6. MP1

    Making PCBs with magazine's paper

    gsmaster, Yes, I also have experience with the yellow stains. I have also had the occasion when the thermostat quit working in a heater and got the etchant too hot. Everything in the etch room that had metal exposed to the air became rusted. I hope you can find a way to post the ingredient that...
  7. MP1

    Making PCBs with magazine's paper

    Not sure about the plexiglass. I made mine with thick pieces of glass and clear RTV. The materials were more readily available to me. Ammonium Persulfate turns blue as the copper is etched. The more copper etched, the bluer it gets, until you cannot see through it very well, either. I think it...
  8. MP1

    Data Sheet K818, K819 and BD705, BD708

    Does anyone have a cross reference chart for KT818, KT819 and BD708, BD705 transistors? For example, is there a TIPxx equivalent or 2Nxxxx equivalent that can be used in their place? Thanks, MP
  9. MP1

    Pulse-width modulator

    There are schematics for 28 different types at the following link: http://www.discovercircuits.com/P/pwm.htm Hope this helps! MP
  10. MP1

    Making PCBs with magazine's paper

    I see nothing wrong with your board. And I have been making boards for quite a few years. Since your traces are thick, the edge is not a problem. In fact, the only place I have seen where this is critical is in microwave circuits where the trace thickness and length is calculated for precise...
  11. MP1

    Inside a TO-3 Transistor case

    Hmmm...That's interesting. What voltage and current have you measured from one? There's not much surface space there. MP
  12. MP1

    Monitor's Led blinking

    The LED on my monitor blinks, too... ;D...when I turn the computer off and forget to shut off the monitor. ;) MP
  13. MP1

    sensitive low frequency filter

    Yes, this is a single op-amp filter with a gain stage ahead of it. So, if you are going to limit your design to only 2 op-amps, you have a choice. Do you want the more attenuation of signal outside of the frequency pass band or do you want more overall gain of your circuit? If you want both, you...
  14. MP1

    Audio IC's

    Yeah, I am not familiar enough with either chip, but they are both audio amp chips. Sometimes one manufacturer makes the same as another and puts their prefix on the existing number. Was hoping that might be another source. You could probably do the same thing on the NEC website. Just find...
  15. MP1

    handy tip for intefacing your PC with projects

    Found it! The program is Quick Basic 4.5. Since it is not freeware, I will not post it. However, it is probably all over the net if you look. ;D With this, you can copy all of your Qbasic code and paste it into this program editor, then click the compile button and you have an EXE file. This...
  16. MP1

    sensitive low frequency filter

    Here is the best you will probably get with two op-amps. I have provided the formula in the drawing. You already have the cap values, you just have to figure the resistors from the frequency of cut-off. Just round the resistor calculated figures to a number that is an actual resistor value. The...
  17. MP1

    handy tip for intefacing your PC with projects

    There is another form of basic that compiles your code to an exe file. It is much nicer than Qbasic because you just enter the name of the exe instead of going into the qbasic editor to run your program. In regards to the other: Using a 386 with only Dos loaded onto it is pretty rare for most of...
  18. MP1

    Audio IC's

    I think it is the same as the TDA2506 from Phillips. This is an obsolete chip, but you can contact Phillips directly and ask for the data sheet at http://www.semiconductors.philips.com/ It is no longer on their website. MP
  19. MP1

    sensitive low frequency filter

    You are looking for a low pass filter? What is the cut off frequency that you desire and how much cut? These are necessary questions before you can build a filter, whether it is built with op-amps or transistors. MP
  20. MP1

    handy tip for intefacing your PC with projects

    Actually, this needs a little more explanation if it is to work for someone stumbling across this for the first time. If you are controlling a stepper motor or anything else from the parallel port, you will need to fool the port into thinking it is connected to a printer. This is done by tying...
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