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  1. KrisBlueNZ

    SPI single line SDI/SDO

    In section 9.1 on page 69 of the PIC16F877 data sheet, the text before the last bulleted list says "For the pins to behave as the serial port function, some must have their data direction bits (in the TRIS register) appropriately programmed" and the second bullet point says "SDO must have...
  2. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    That circuit won't work as designed. I don't know why the simulator thinks it will. The problem is the NPN you're using to invert the output signal to drive the second PNP. Its base will clamp the comparator's output to about 0.7V above the 0V rail. In the real world if you built this circuit...
  3. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    It's a long story to explain why 2.5 ohms is too low. Simply put, it makes the upper and lower voltage thresholds equal to the output voltage swing, which is (a) variable, depending on temperature and other factors, and (b) too close to the positive supply for most op-amps to deal with. Even if...
  4. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    The op-amp circuit is fine, though I'm not sure what value your positive feedback resistor is - is it 2.5 ohms? It should be around the same value as the other two resistors connecting to the non-inverting input. The disadvantages of the op-amp are that you need an op-amp with a full output...
  5. KrisBlueNZ

    using PORT A of 16f870

    The use of RA0~3, RA5 and RE0~2 is controlled by the PCFG3~0 bits in ADCON1 according to a big table. The device only supports certain combinations, and those bit settings also determine where the ADC gets its positive and negative reference voltages from. Look through that table for a suitable...
  6. KrisBlueNZ

    When or where use EPROM and EEPROM?

    EPROMs and EEPROMs are types of PROMs - programmable read-only memories. PROMs store information as an array of bits (binary digits), each of which can be 1 or 0. They are normally grouped into sets of 8 or 16. The information may represent program instructions (a type of software known as...
  7. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    It depends how accurate you need the duty cycle to be. You can get close to 50% using a relatively low value resistor from pin 7 to VCC and a higher value for the other resistor. Also you can take the feedback from pin 3 instead of pin 7 if there's a good symmetrical voltage swing at the...
  8. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    But you don't want to use a 555? True. But you can make a square wave oscillator with one op-amp and use the other to invert the signal. But that requires about 5 external components. Are you talking about the two PNPs? They will be OK. I'm not sure what you mean. Assume the intensity...
  9. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    I thought I had the Java plugin installed, but you're right, I didn't. That's a strange looking circuit! Oh, I see it now. Yes, I agree that a micro would be the best choice, especially if you have programming experience. You'll still need the transistor buffers, but you could do the voltage...
  10. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    That link doesn't take me to your schematic. It probably does on your machine because you have cookies that tell the site which circuit you are working on, but we don't have those cookies, so you'll need another way to direct us to the schematic. Or you could take a screen capture, crop it...
  11. KrisBlueNZ

    Sound Level Meter

    That circuit should work OK. Post some photos of your construction. What kind of microphone did you use? You need an electret type - a small cylindrical thing with a hole in one end and two solder connections at the other, one of which is connected to the metal part. This is the negative side...
  12. KrisBlueNZ

    Modifying 110v device to run on 240v

    I don't think that makes sense. Given that nearly all the power drawn by the element is converted into heat energy, and that most of that energy can't go anywhere except into the water being heated, I don't see what "thermal efficiency" even means in this context. I tried to explain why, but I...
  13. KrisBlueNZ

    Flashing program data to AT89S2051

    Yeah. You'd think that Atmel would make an effort to support their own products! Yeah, I'm sure you'll find LOTS of things for them to do. I've used many types of MCUs and IMO, of all the 8-bit MCUs, the PIC has the worst architecture. The 8-bit PIC core design is very restrictive and the...
  14. KrisBlueNZ

    Flashing program data to AT89S2051

    Yeah. Many companies are trying to discourage end users from making their own device programmers. Partly because a lot of DIY programmers don't work very well and they don't want their products associated with that. Microchip (maker of the PIC devices) and Atmel (AVRs and your 2051, and others)...
  15. KrisBlueNZ

    Flashing program data to AT89S2051

    Hello and welcome to Electronics Point :-) Thank you for giving so much information in your question! The AT89S2051 data sheet describes two programming methods: parallel and serial. Serial is simplest to connect, so let's go with that. The serial programming method doesn't use asynchronous...
  16. KrisBlueNZ

    Op-amps and transistors for audio

    Great! Yes. The ones with a single input are the simplest to use because you don't need any feedback or biasing components. You may need a DC blocking capacitor between the wiper of your volume potentiometer and the input pin. BTW, use a logarithmic potentiometer for the volume control, not linear.
  17. KrisBlueNZ

    Designing a Converter!

    OK, I've just looked at your complete schematic from post #15. 1. The MCP6044's input offset voltage will contribute up to +/- 0.6% error. Resistor tolerances will also cause errors. What type of resistors are you going to use? 2. What is your error budget? 3. The op-amps need to be powered...
  18. KrisBlueNZ

    (Electro)Magnetic Levitation

    That can't be right. The LED needs positive voltage on its anode relative to its cathode. Do you have a resistor in series with it? You need one, otherwise the LED will prevent the Hall sensor output from pulling all the way up (or down, depending on how the LED is connected). I suggest you...
  19. KrisBlueNZ

    Component questions (transistor, capacitor)

    Re the schematic in post #25, it is actually misleading, because the resistor-transistor device shouldn't be shown as a transistor. When I started using them in my designs, I had to create a new circuit symbol for them, that showed the resistors as tiny rectangles. If the schematic editor you...
  20. KrisBlueNZ

    Modifying 110v device to run on 240v

    I agree with Steve. You would be dissipating twice as much power, which is a VERY significant factor, and your peak current would be twice as high, which would stress everything in the system. Remember that the 110VAC system already operates at twice the current of a 230VAC system (for a given...
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