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  1. KrisBlueNZ

    Designing a Time Delayed Relay

    I agree green is a better colour. Green LEDs aren't as efficient as red LEDs but that's less important than having the right colour. While I was working on the updated schematic I noticed that we can't use pin 2 of the MCU for the second Allegro signal - it doesn't have ADC input capability so...
  2. KrisBlueNZ

    preamp led driver help

    Hi there and welcome to Electronics Point :) So you want to drive an LED from the headphone output of your phone. You want to play square wave signals through the headphone output, and you want the LED to reproduce the signal. So when the square wave is positive, the LED lights up, and when...
  3. KrisBlueNZ

    Help with polarity switching due to light levels

    Yes, it's pretty easy. If you use LDRs (light dependent resistors), you can connect them in series across the power supply. The node tap voltage will be at half supply if equal light is falling on both. If more light is falling on the one that connects to VCC, it will pull the centre node up to...
  4. KrisBlueNZ

    Is there a chance to get blind or serious physical damage while prototyping ?

    You're very unlikely to electrocute yourself with 40V (but keep any open cuts covered), but low voltages can be dangerous if high currents are possible, which is why you need to be careful when working on vehicle electrical systems. If an item of jewellery, e.g. a wedding ring, shorts across the...
  5. KrisBlueNZ

    First Digital Logic Circuit

    That looks fine. You don't need the OR gate. You have A and B, and you have inverters to generate not A and not B. You can just use the three AND gates to detect the three relevant combinations of those signals. Edit: If you build up this circuit, remember that you need resistors in series...
  6. KrisBlueNZ

    555 voltage controlled oscillator question

    Rleo is wrong; you can operate a 555 with pin 5 over quite a wide range. But it's not a very ideal VCO - the frequency vs. voltage graph is not linear, and an increasing voltage causes a decreasing frequency (over most of the range, at least). You can improve it by adding external components -...
  7. KrisBlueNZ

    Replacing paper capacitors

    Electrolytics are polarised. It's unlikely that you will be replacing a non-polarised capacitor with an electrolytic, because their value ranges don't overlap much. So you would normally replace a non-polarised capacitor with a non-polarised capacitor, and a polarised capacitor with a polarised...
  8. KrisBlueNZ

    Series pass voltage regulator not working as expected

    Yes, you can add a load resistor. You can also make a circuit that detects loss of the AC mains input to the bridge rectifier (with a short delay, say 30~40 ms) and then enables a discharge resistor; this means you can discharge the capacitors quite quickly after power-off without wasting a lot...
  9. KrisBlueNZ

    penetration of em spectrum's

    bhuvanesh, you are asking questions that can easily be answered with a Google search. This is not really appropriate; it wastes our time, and yours. You know how to use Google, right? You know how to choose appropriate search terms and how to modify your search terms to find information that's...
  10. KrisBlueNZ

    PID Controller from Antiquated IPAQ 4150

    Hello and welcome to Electronics Point :-) The actual calculations involved in PID loops are not that complicated. You need to look into what input and output signals you will need, and how to get them into and out of your IPAQ. I expect you will need at least one temperature monitoring...
  11. KrisBlueNZ

    Help Getting Started with PIC Microcontrollers

    To learn. For serious commercial production, yes, you would buy the full version of the compiler. What is your point?
  12. KrisBlueNZ

    Please help !!

    If your old devices were programmed without code protection, you can read the data out of them. Start with the Microchip PICkit 3 user's guide (DS51795A) in section 9.4.1.
  13. KrisBlueNZ

    Help Getting Started with PIC Microcontrollers

    Yes. That's a good question. I don't know of any foolproof way, except I think all the PIC18F... devices are high-end. The selection guides on Microchip's and Digikey's web sites don't tell you either. The main distinguishing factor is the Flash ROM width, i.e. how many bits wide the...
  14. KrisBlueNZ

    Help Getting Started with PIC Microcontrollers

    No, C will use a lot more code space than assembly language, especially on baseline and mid-range devices. I'd estimate between twice and four times as much. But that's partly because it allows you to write your code the way it should be written, rather than having to customise the design of the...
  15. KrisBlueNZ

    Please help !!

    Are you totally sure there are no code changes? Perhaps you made a tiny modification that wasn't supposed to affect anything, but accidentally introduced a bug? Perhaps one of the project settings is wrong? Can you program a new device with a hex file that was actually built in the past when...
  16. KrisBlueNZ

    Help Getting Started with PIC Microcontrollers

    I wouldn't, personally, but it's possible. If you just want to replace a few timers and some glue logic, then yes, you can program it in C. Have you seen the code these PIC compilers produce? The code is not very efficient, because the baseline and mid-range PIC architectures are so poorly...
  17. KrisBlueNZ

    Help Getting Started with PIC Microcontrollers

    I don't think that's necessarily true. And I'm an assembly programmer from way back. You do need to learn how the peripherals work, but most of the messy implementation details (due to the poor design of the processor core of the small PICs) will be taken care of by the compiler and it's...
  18. KrisBlueNZ

    Help Getting Started with PIC Microcontrollers

    Yes, you will need another board. I think you can buy a PICkit development package which includes at least one board to hold PICs during programming, but normally, programming is done in the final application circuit board using ICSP - in-circuit serial programming. You include a 5-pin connector...
  19. KrisBlueNZ

    calculation of change in voltage in zener diode

    I'm not sure about your calculations, but that's the right answer. So that's telling you that if your zener current is nominally 10 mA but varies by ±10% (i.e. ±1 mA), the zener voltage will vary by ±0.2%. This is intended to show you that variations in zener current DO cause variations in...
  20. KrisBlueNZ

    calculation of change in voltage in zener diode

    This section is showing you how to calculate the change in voltage across a zener diode when the current into the zener diode is varied, using the zener diode's dynamic resistance defined at a particular current. This shows you how stable the zener voltage will be when the current varies...
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