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  1. KrisBlueNZ

    Current Mirrors

    Saturation is (VB > VC > VE). And that's why the input transistor can never be in saturation - because VB = VC. There is only one current path into that transistor - the input of the current mirror, which comes from the driving circuit - R1 in that case. Some of this current goes into the base...
  2. KrisBlueNZ

    Help: High current, adjustable voltage output

    Hi and welcome to Electronics Point :-) It would really help if you explained more about this project. What's the purpose? What will the input be coming from? What will the output be going to? Any relevant diagrams or photos would be helpful too.
  3. KrisBlueNZ

    Next/previous switching a multiplexer

    Right. The activity indicator receives the MIDI data using an optocoupler, converts it to a logic-level signal so it can detect it easily and illuminate the LED, and then re-transmits it. There is an inherent skew introduced by the optocoupler, and it will affect the signal. The simple solution...
  4. KrisBlueNZ

    Formula to get voltage on circuit

    Yes, this does look like a homework question. I've moved it to the homework forum. The first thing to do is to redraw that confusing diagram in a more familiar way. Now you can see that the batteries are in series, and the resistors form a voltage divider across their combined voltage. If...
  5. KrisBlueNZ

    Designing a Time Delayed Relay

    OK. I'll specify the 30A one on the schematic. OK, cool. I wouldn't go for a PICkit 1 - I think they're pretty old. Here are three other options: PICkit 2 starter kit: http://www.digikey.com/product-detail/en/DV164120/DV164120-ND/806160 USD 66 PICkit 3 programmer only...
  6. KrisBlueNZ

    Current Mirrors

    Oh, thanks. I thought I was rambling a bit. Actually, Q2 is NOT in saturation. That's actually impossible in a current mirror! You need to understand what saturation actually IS. The following description is for NPN transistors; just reverse the polarities for PNPs. Some of the details aren't...
  7. KrisBlueNZ

    Motion sensor lighting with a difference

    OK. I'm a bit busy for the next few days - I have a project porting some code to a new compiler, and I have an exam for a qualification that I don't really want... So I'll get in touch later in the week. How many units do you want made? If it's only one or two, I can build them up on stripboard...
  8. KrisBlueNZ

    Designing a Time Delayed Relay

    No. While the motor is running, current will be flowing through the ACS712's sensing path. It will have the usual sinewave shape. So the MCU will expect to see a varying voltage on the ACS712's output. When that varying signal stops varying, and settles around half VCC, the MCU knows that the...
  9. KrisBlueNZ

    Designing a Time Delayed Relay

    LOL :) Right. You just let me know what you want it to do. Yes, that's fine if we use the PIC12F1571. Since we don't need to detect the actual value of the current, just detect that something is happening, it doesn't really matter which scale we choose for the ACS712 - we could even use the 5A...
  10. KrisBlueNZ

    Wireless trigger for LEDs and buzzers

    OK, so the time between one transition and the next will be about 1 µs. The timings are given on page 49 of the nRF24L01 specification. The relevant parameter is Tdc, data to clock setup time, shown on the diagram on page 48. This parameter is the minimum amount of time needed by the nRF24L01...
  11. KrisBlueNZ

    C vs C++ with uControllers

    Whether SPI is done with a peripheral or by bit-banging doesn't make much difference in this context. The main factors that affect an architecture's usability with higher-level, more abstrated languages are the amount of RAM and ROM, the speed, and the number of registers (especially pointer...
  12. KrisBlueNZ

    Current Mirrors

    The currents are not equal because in that circuit, the current flow through R2 and Q1 is limited by R2 and the 12V supply it is connected to. When a current mirror is operating normally, the current in the output path (Q1's collector) is limited by Q1. Q1 conducts (from collector to emitter)...
  13. KrisBlueNZ

    Wireless trigger for LEDs and buzzers

    That's good that you recognised that as a possible issue. It won't be a problem unless you're using a very fast PIC with a slow peripheral such as a CD4000-series device, but it's a good idea to check.
  14. KrisBlueNZ

    Which voltage transformer for a laser printer

    According to https://en.wikipedia.org/wiki/American_wire_gauge 14 AWG is rated for 20A and 12 AWG for 25A. (Lower AWG numbers are thicker.) Those figures are for solid cores; wires should be about 5% thicker if they're stranded. Personally I would go for the thickest I could find, provided that...
  15. KrisBlueNZ

    Toyota Rev Counter

    Yes, 10 µF and 22 µF in series works out to about 6.8 µF, but the fact that they chose 6.8 µF instead of a common, "close enough" value like 4.7 µF or 10 µF could imply that it's a fairly critical value, and normal "close enough" electrolytics may not be accurate enough. Without being able to...
  16. KrisBlueNZ

    Needing help with sensor/meter project

    Can you upload a photo of your construction? Can you upload a schematic? Just a photo of a drawing on paper is enough.
  17. KrisBlueNZ

    Ir led modulation

    Yes: IrDA: https://en.wikipedia.org/wiki/Infrared_Data_Association Yes. The higher the data speed, the shorter the range, and the more critical the path.
  18. KrisBlueNZ

    C vs C++ with uControllers

    LOL Chris :-) BTW I was promoted to moderator in November. I guess my main argument against using the object-oriented features of C++ on small micros is the memory usage, and the inefficiency of accessing data objects by reference or pointer. If you want to write a compact program using static...
  19. KrisBlueNZ

    C vs C++ with uControllers

    You can compile C code with a C++ compiler. But the code is still C code. Likewise, you can also compile assembly language with a C compiler - most of them have some kind of inline assembler capability. But that doesn't make it C code! Object oriented programming forces the programmer to really...
  20. KrisBlueNZ

    Bypass standby switch

    I don't know. Have a look through the manual and see if it mentions any special function that you can get by holding the button down. I would just jam a toothpick in there, and try it out manually and see whether it starts up each time you plug it in, and seems to work normally for a reasonable...
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