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  1. KrisBlueNZ

    Modding a circuit

    If you want the amplifier stage to amplify without clipping, so the diodes are the only clipping element, you should use a voltage divider to provide the base bias. I would recommend using high resistances in the voltage divider, and a Darlington transistor, to give high input impedance so you...
  2. KrisBlueNZ

    Modding a circuit

    Relayer, your gain adjustment in the emitter leg is wrong. You should use a fixed resistor to set the DC conditions, and a potentiometer and capacitor in series, in parallel with the fixed resistor. The way you have it connected will mean that the gain will not vary much, since the capacitor...
  3. KrisBlueNZ

    Modding a circuit

    You can vary the stage gain by putting a variable resistor (a potentiometer with only two terminals used) and a capacitor in series with it, all in parallel with the emitter resistor. In this case it's probably best to use a logarithmic potentiometer. And you're probably right that the...
  4. KrisBlueNZ

    Modding a circuit

    Yes. Most of your question is too vague for me to know how to answer you. Regarding your last question, click here.
  5. KrisBlueNZ

    9v preamp for acoustic guitar

    Hi kiwi, welcome to the forums :-) I don't see any connection to the middle pin of the JFET. Also several connections that should be grounded aren't connected to the ground plane. You also need to specify the part number of the JFET so we know its pinout. Personally I would make the layout more...
  6. KrisBlueNZ

    how to figure out the power consumption of a circuit

    P = V I. Power (in watts) is voltage (volts) multiplied by current (amps). So you need to measure, or calculate, the current going into the circuit, and multiply it by the voltage applied to the circuit. You may also need to measure (or calculate) the current in different situations. The current...
  7. KrisBlueNZ

    Engine shut down circuit needed

    Yes I'm for real. I don't know you personally, so don't take it personally. I know it's a "safety circuit"; that's obvious. We have no way to KNOW what you intend to do with it. Perhaps if you explain the situation in detail you may be more convincing. I have seen people deliberately mislead...
  8. KrisBlueNZ

    Engine shut down circuit needed

    A warning to anyone who is considering offering to help with this project. Killing a car engine while it's running could be very unsafe. Another electronics forum web site I visit has a formal policy of "no automotive modifications" because of the risks. This despite the claim that the circuit...
  9. KrisBlueNZ

    Analog Audio Signal Crypting

    I'd say you'll need to encode every bit of every byte. Look for public domain encryption systems and pass the digitised data through it just like it was a file. The encrypted data will be uncompressable so you'll need plenty of bandwidth between the sending PIC and the receiving PIC. If the...
  10. KrisBlueNZ

    Question on power failure circuit

    Hmm, that's an interesting diagram. Once again, I'm glad you're not my doctor! Yes, the 555 will work with that circuit, or without D2 if you tie pin 2 to pin 6. In that setup, it operates as a Schmitt trigger (Wikipedia it) with its trigger voltages (on pin 2/6) at 2/3 and 1/3 of its power...
  11. KrisBlueNZ

    Question on power failure circuit

    Hi kong :-) So, you got curious and decided to start removing components to see whether it would still work. Well, I'm glad you're not my doctor! You removed D2, R2 and C2, and it still beeps when the power fails? I guess your piezo device must include an oscillator. You just need to apply DC...
  12. KrisBlueNZ

    Picking the correct diode

    I suggested the capacitor in parallel with the diode to protect the diode from voltage spikes from parasitic inductances in the wiring. Schottky diodes can't handle overvoltage and can be damaged by voltage spikes. If you use one, use a good quality capacitor and connect it directly across the...
  13. KrisBlueNZ

    help with coupling components

    Hi jrb and welcome to the forums :-) The diagram on page 6 of the TDA7052 data sheet shows you how to use the device. See the two decoupling capacitors across the supply rails? You should have those in your design; they're needed for stability. That diagram also shows you how to drive the...
  14. KrisBlueNZ

    Picking the correct diode

    I'd recommend a Schottky diode rated for at least as much current as the motor draws, and safely more than the maximum supply voltage. It's probably a good idea to add a small capacitor e.g. 10 nF in parallel with the diode. These diodes are all under USD 1.00 and available in one-off quantities...
  15. KrisBlueNZ

    Mutiple clients with one Microcontroller unit

    OK. RS-485 is a multi-drop bus. This means that every device on the bus will see every transmission. So you will need to design your protocol so that each device on the bus can identify messages that relate to it, and ignore messages that don't. This means that messages must include an address...
  16. KrisBlueNZ

    Mutiple clients with one Microcontroller unit

    I see. Thanks for explaining the application; it makes a big difference. So you have an 8051 "slave" connected to each RFID reader, and you want to use RS-485 to communicate between the central processor and the slave processors? Are the slave processors physically distant from each other? I...
  17. KrisBlueNZ

    Merry Christmas and a happy new year

    Merry Fun-Family-Partying everyone!
  18. KrisBlueNZ

    Make a "blinker" for LED panel?

    In Steve's calculations in post #49 on this thread, he estimates 2.7W total radiant energy for the grow light panel. The WARP75 has 3.5W radiant energy in an area of about 58 square centimetres. To get this radiant energy density, you would have to reduce the grow light panel area to about 45...
  19. KrisBlueNZ

    Make a "blinker" for LED panel?

    Thanks for that reference. The mention of continuous vs. pulsed light is on page 231, right column, where the author (Bariolet) says: "The influence of CW [continuous] versus pulsing mode, as well as precise pulsing parameters [...], on cellular response has not been fully studied. To date...
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